Eelgrass Sex is Strange

Photo by Fredlyfish4 licensed by CC BY-SA 4.0

Pollination may seem like a strange thing to us humans. Whereas we only require two of us to accomplish reproduction, plants have to utilize a third party. The most familiar cases include insects like bees and butterflies. Unique examples include birds, bats, and even lizards. Many plants forego the need of an animal and instead rely on wind to broadcast copious amounts of pollen into the air in hopes that it will randomly bump into a receptive female organ.

This has worked very well for terrestrial plants but what about their aquatic relatives? Water proves to be quite an obstacle for the methods mentioned above. Some species get around this by thrusting their flowers above the surface but others don't bother. One genus in particular has evolved a truly novel way of achieving sexual reproduction without having to leave its aquatic environment in any way.

Photo by eyeweed licensed by CC BY-NC-ND 2.0

Meet the Vallisnerias. Commonly referred to as tape or eelgrasses, this genus of aquatic plants has been made famous the world over by their use in the aquarium trade. In the wild they grow submerged with their long, grass-like leaves dancing up into the water column. Where they are native, eelgrasses function as an important component of aquatic ecology. Everything from fish and crustaceans all the way up to manatees utilize tape grass beds for both food and shelter. Eelgrasses stabilize stream beds and shorelines and even act as water filters.

All this is quite nice but, to me, the most interesting aspect of Vallisneria ecology is their reproductive strategy. Whereas they will reproduce vegetatively by throwing out runners, it is their method of sexual reproduction that boggles the mind. Vallisneria are dioecious, meaning individual plants produce either male or female flowers. The female flowers are borne on long stalks that reach up to the water surface. Once there they stop growing and start waiting. Because of their positioning, water tension causes a slight depression around the flowers at the surface. The depression resembles a little dimple with a tiny white flower in the center.

A female Vallisneria flower. Photo by eyeweed licensed by CC BY-NC-ND 2.0

Male Vallisneria flowers floating on the water surface. Photo by eyeweed licensed by CC BY-NC-ND 2.0

Male flowers are very different. Much smaller than the female flowers, a single inflorescence can contain thousands of individual male organs. As they mature underwater, the male flowers break off from the inflorescence and float to the surface. Similar to wind pollinated terrestrial plants, Vallisneria use water currents to disperse their pollen. Once at the surface, the tiny male flowers float around like little pollen-filled rafts.

If a male flower floats near the dimple created by a female flower, it will slide down into the funnel-like depression where it will contact with the female flowers. This is how pollination is achieved. Once pollinated, hormonal changes signal the stem of the female flower to begin to coil up like a spring, drawing the developing seeds safely underwater where they will mature. Eventually hundreds of seeds are released into the water currents.

After pollination, the stem of the female flower coils up, drawing the ripening ovaries safely underwater. Photo by Peter M. Dziuk [source]

The Vallisneria are incredible aquatic plants. Their bizarre reproductive strategy has ensured that these plants never really have to leave the water. The fact that they can also reproduce vegetatively means that many species are very successful plants. In fact, some species have become noxious invasive weeds where they have been introduced far outside of their native range. If you own these plants in any way, do take the necessary measures to ensure that they never have the chance to become invasive.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1]

The Fungus-Mimicking Mouse Plant

The mouse plant (Arisarum proboscideum) is, to me, one of the most charming aroids in existence. Its small stature and unique inflorescence are a joy to observe. It is no wonder that this species has attained a level of popularity among those of us who enjoy growing oddball plants. Its unique appearance may be reason enough to appreciate this little aroid but its pollination strategy is sure to seal the deal.

The mouse plant is native to shaded woodlands in parts of Italy and Spain. It is a spring bloomer, hitting peak flowering around April. It has earned the name “mouse plant” thanks to the long, tail-like appendage that forms at the end of the spathe. That “tail” is the only part of the inflorescence that sticks up above the arrow-shaped leaves. The rest of the structure is presented down near ground level. From its stature and position, to its color, texture, and even smell, everything about the inflorescence is geared around fungal mimicry.

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The mouse plant is pollinated by fungus gnats. However, it doesn’t offer them any rewards. Instead, it has evolved a deceptive pollination syndrome that takes advantage of a need that all living things strive to attain - reproduction. To draw fungus gnats in, the mouse plant inflorescence produces compounds that are said to smell like fungi. Lured by the scent, the insects utilize the tail-like projection of the spathe as a sort of highway that leads them to the source.

Once the fungus gnats locate the inflorescence, they are presented with something incredibly mushroom-like in color and appearance. The only opening in the protective spathe surrounding the spadix and flowers is a tiny, dark hole that opens downward towards the ground. This is akin to what a fungus-loving insect would come to expect from a tiny mushroom cap. Upon entering, the fungus gnats are greeted with the tip of the spadix, which has come to resemble the texture and microclimate of the underside of a mushroom.

Anatomy of a mouse plant inflorescence [SOURCE]

This is exactly what the fungus gnats are looking for. After a round of courtship and mating, the fungus gnats set to work laying eggs on the tip of the spadix. Apparently the tactile cues are so similar to that of a mushroom that the fungus gnats simply don’t realize that they are falling victim to a ruse. Upon hatching, the fungus gnat larvae will not be greeted with a mushroomy meal. Instead, they will starve and die within the wilting inflorescence. The job of the adult fungus gnats is not over at this point. To achieve pollination, the plant must trick them into contacting the flowers themselves.

Both male and female flowers are located down at the base of the structure. As you can see in the pictures, the inflorescence is two-toned - dark brown on top and translucent white on the bottom. The flowers just so happen to sit nicely within the part of the spathe that is white in coloration. In making a bid to escape post-mating, the fungus gnats crawl/fly towards the light. However, because the opening in the spathe points downward, the lighted portion of the structure is down at the bottom with the flowers.

The leaves are the best way to locate these plants. Photo by Meneerke bloem licensed under CC BY-SA 4.0

Confused by this, the fungus gnats dive deeper into the inflorescence and that is when they come into contact with the flowers. Male and female flowers of the mouse plants mature at the exact same time. That way, if visiting fungus gnats happen to be carrying pollen from a previous encounter, they will deposit it on the female flowers and pick up pollen from the male flowers all at once. It has been noted that very few fungus gnats have ever been observed within the flower at any given time so it stands to reason that with a little extra effort, they are able to escape and with any luck (for the plant at least) will repeat the process again with neighboring individuals.

The mouse plant does not appear to be self-fertile so only pollen from unrelated individuals will successfully pollinate the female flowers. This can be a bit of an issue thanks to the fact that plants also reproduce vegetatively. Large mouse plant populations are often made up of clones of a single individual. This may be why rates of sexual reproduction in the wild are often as low as 10 - 20%. Still, it must work some of the time otherwise how would such a sophisticated form of pollination syndrome evolve in the first place.

Photo Credit: [1] [2] [3]

Further Reading: [1] [2]

A Palm With a Unique Pollination Syndrome

Photo by Dr. Scott Zona licensed under CC BY-NC 2.0

I would like to introduce you to the coligallo palm (Calyptrogyne ghiesbreghtiana). The coligallo palm is a modest palm, living out its life in the understory of wet, tropical forests from Mexico to Panama. To the casual observer, this species doesn’t present much of anything that would seem out of the ordinary. That is, until it flowers. Its spike-like inflorescence is covered in fleshy white flowers that smell of garlic and as far as we know, the coligallo palm is the only palm that requires bats for pollination.

Flowering for this palm occurs year round. At first glance, the inflorescence doesn’t appear out of the ordinary but that is where close observation comes in handy. The more scrutiny they are given, the more strange they appear. As mentioned, the flowers are bright white in color and they smell strongly of garlic. Also, they are protandrous, meaning the male flowers are produced before the female flowers.

Photo by Dr. Scott Zona licensed under CC BY-NC 2.0

After the male flowers have shed their pollen, there is a period of a few days in which no flowers are produced. Then, after 3 to 4 nights of no flowers, female flowers emerge, ready to receive pollen. Each flower only opens at night and does not last for more than a single evening. Protandry is an excellent strategy to avoid self-pollination. By separating male and female flowers in time, each plant can assure that its own pollen will not be deposited back onto its own stigmas. The fact that the coligallo palm flowers year-round means that there is always a receptive plant somewhere in the forest.

The oddities do not end there. Both male and female flowers are covered in a fleshy tube that must be removed for pollination to occur successfully. Removal of the tube is what actually exposes the reproductive organs and allows pollen transfer to occur. Often times, the flowers of the coligallo palm are dined upon by katydids and other insect herbivores. This does not result in pollination as they completely destroy the flower as they eat. Considering the success of this plant across its range, it stands to reason that something else must provide ample pollination services.

Two species of bat visiting coligallo palm inflorescences: A) A perching Artibeus bat feeding on male flowers and B) a hovering Glossophaga bat feeding on female flowers.

As it turns out, bats are that pollinator. The job of pollination is not accomplished by a single species of bat either. A few species have been observed visiting the inflorescences. Apparently the bright color and strong odor of the flowers acts as a calling card for flower-feeding bats throughout these forests. Interestingly, the feeding mechanism of each species of bat differs as well. Some bats hover at the inflorescence like hummingbirds, chewing off the fleshy tube from individual flowers as they go. Other bats prefer to perch on the inflorescence itself, crawling all over it as they eat. These different feeding behaviors actually result in different levels of pollination. Though both forms do result in seed set, perching bats appear to be the most effective pollinators of the coligallo palm.

The reason for this is due to the fact that perching bats not only spend more time on the inflorescence, their bodies come into contact with far more flowers as they feed. Hovering bats, on the other hand, only manage to contact a few flowers with their snout at a time. So, despite the variety of bats recorded visiting coligallo palms, the perching bats appear to provide the best pollination services.

A coligallo palm infructescence showing signs of ample pollination. Photo by Dick Culbert licensed under CC BY 2.0

The role of perching bats in the ecology of this palm species does not end with pollination either. It turns out, they also play a crucial role in the dispersal of certain mites that live on the palm flowers. Flower mites live on plants and consume tiny amounts of pollen and nectar. As you can imagine, their small size makes it incredibly difficult for them to find new feeding grounds. This is where perching bats come into play.

It was discovered that besides pollen, perching bats also carried considerable loads of flower mites in their fur. The mites crawl onto the bat as they visit one inflorescence and climb off when they visit another. This is called phoresy. The bats are not harmed by these hitchhikers but are essential to the mite lifecycle. Thanks to their bat transports, the mites are able to make it to new feeding grounds far away from their original location. Though little is known about these mites, it has been suggested that the mites living on the coligallo palm are unique to that species and probably feed on no other plants.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3]

Twinspurs & Their Pollinators

© El Grafo / CC-BY-SA-3.0 (via Wikimedia Commons)

Garden centers and nurseries always have something to teach me. Though I am largely a native plant gardener, the diversity of plant life offered up for sale is always a bit mind boggling. Perusing the shelves and tables of myriad cultivars and varieties, I inevitably encounter something new and interesting to investigate. That is exactly how I came to learn about the twinspurs (Diascia spp.) and their peculiar floral morphology. Far from being simply beautiful, these herbaceous plants have evolved an interesting relationship with a small group of bees.

Diascia whiteheadii. Photo by Ragnhild&Neil Crawford licensed under CC BY-SA 2.0

The genus Diascia comprises roughly 70 species and resides in the family Scrophulariaceae. They are native to a decent chunk of southern Africa and have adapted to a range of climate conditions. Most are annuals but some have evolved a perennial habit. The reason these plants caught my eye was not the bright pinks and oranges of their petals but rather the two spurs that hang off the back of each bloom. Those spurs felt like a bit of a departure from other single-spurred flowers that I am used to so I decided to do some research. I fully expected them to be a mutation that someone had selectively bred into these plants, however, that is not the case. It turns out, those two nectar spurs are completely natural and their function in the pollination ecology of these plants is absolutely fascinating.

Diascia rigescens photo by Dinkum licensed under CC BY-SA 3.0

Not all Diascia produce dual spurs on each flower but a majority of them do. The spurs themselves can vary in length from species to species, which has everything to do with their specific pollinator. The inside of each spur is not filled with nectar as one might expect. Instead, the walls are lined with strange trichomes and that secrete an oily substance. It’s this oily substance that is the sole reward for visiting Diascia flowers.

Diascia megathura (a) inflorescenc with arrows indicating spurs and (b) cross sectioned spur showing the trichomes secreting oil (Photos: G. Gerlach).

If you find yourself looking at insects in southern Africa, you may run into a genus of bees called Rediviva whose females have oddly proportioned legs. The two front legs of Rediviva females are disproportionately long compared to the rest of their legs. They look a bit strange compared to other bees but see one in action and you will quickly understand what is going on. Rediviva bees are the sole pollinators of Diascia flowers. Attracted by the bright colors, the bees alight on the flower and begin probing those two nectar spurs with each of their long front legs.

If you look closely at each front leg, you will notice that they are covered in specialized hairs. Those hairs mop up the oily secretions from within each spur and the bee then transfers the oils to sacs on their hind legs. What is even more amazing is that each flower seems to have entered into a relationship with either a small handful or even a single species of Rediviva bee. That is why the spur lengths differ from species to species - each one caters to the front leg length of each species of Rediviva bee. It is worth noting that at least a few species of Diascia are generalists and are visited by at least a couple different bees. Still, the specificity of this relationship appears to have led to reproductive isolation among many populations of these plants, no doubt lending to the diversity of Diascia species we see today.

Diascia 'Coral Belle' Photo by KENPEI licensed under CC BY-SA 3.0

The female bees do not eat the oils they collect. Instead, they take them back to their brood chambers, feed them to their developing offspring, and use what remains to line their nests. At this point it goes without saying that if Diascia were to disappear, so too would these bees. It is incredible to think of the myriad ways that plants have tricked their pollinators into giving up most, if not all of their attention to a single type of flower. Also, I love the fact that a simple trip to a garden center unlocked a whole new world of appreciation for a group of pretty, little bedding plants. It just goes to show you that plants have so much more to offer than just their beauty.

Photo Credits: [1] [2] [3] [4] [5] [6]

Further Reading: [1] [2] [3] [4]

A New Case of Lizard Pollination from South Africa

With its compact growth habit and small, inconspicuous flowers tucked under its leaves, it seems like Guthriea capensis doesn’t want to be noticed. Indeed, it has earned itself the common name of '“hidden flower.” That’s not to say this plant is unsuccessful. In fact, it seems to do just fine tucked in among high-elevation rock crevices of its home range along the Drakensberg escarpment of South Africa. Despite its cryptic nature, something must be pollinating these plants and recent research has finally figured that out. It appears that the hidden flower has a friend in some local reptiles.

Lizard pollination is not unheard of ([1] & [2]), however, it is by no means a common pollination syndrome. This could have something to do with the fact that we haven’t been looking. Pollination studies are notoriously tricky. Just because something visits a flower does not mean its an effective pollinator. To investigate this properly, one needs ample hours of close observation and some manipulative experiments to get to the bottom of it. Before we get to that, however, its worth getting to know this strange plant in a little more detail.

The hidden flower is a member of an obscure family called Achariaceae. Though a few members have managed to catch our attention economically, most genera are poorly studied. The hidden flower itself appears to be adapted to high elevation environments, hence its compact growth form. By hugging the substrate, this little herb is able to avoid the punishing winds that characterize montane habitats. Plants are dioecious meaning individuals produce either male or female flowers, never both. The most interesting aspect of its flowers, however, are how inconspicuous they are.

The hidden flower (Guthriea capensis) in situ.

Flowers are produced at the base of the plant, out of site from most organisms. They are small and mostly green in color except for the presence of a few bright orange glands near the base of the style, deep within the floral tube. What they lack in visibility, they make up for in nectar and smell. Each flower produced copious amounts of sticky, sugar-rich nectar. They are also scented. Taken together, these traits usually signal a pollination syndrome with tiny rodents but this assumption appears to be wrong.

Based on hours of video footage and a handful of clever experiments, a team of researchers from the University of KwaZulu-Natal and the University of the Free State have been able to demonstrate that lizards, not mammals, birds, or insects are the main pollinators of this cryptic plant. Two species of lizard native to this region, Pseudocordylus melanotus and Tropidosaura gularis, were the main floral visitors over the duration of the study period.

Pseudocordylus melanotus

Tropidosaura gularis photo © 2009 Serban Proches licensed under CC BY-SA 2.5

Visiting lizards would spend time lapping up nectar from several flowers before moving off and in doing so, picked up lots of pollen in the process. Being covered in scales means that pollen can have a difficult time sticking to the face of a reptile but the researchers believe that this is where the sticky pollen comes into play. It is clear that the pollen adheres to the lizards’ face thanks to the fact that they are usually covered in sticky nectar. By examining repeated feeding attempts on different flowers, they also observed that not only do the lizards pick up plenty of pollen, they deposit it in just the right spot on the stigma for pollination to be successful. Insect visitors, on the other hand, were not as effective at proper pollen transfer.

Conspicuously absent from the visitation roster were rodents. The reason for this could lie in some of the compounds produced within the nectar. The team found high levels of a chemical called safranal, which is responsible for the smell of the flowers. Safranal is also bitter to the taste and it could very well serve as a deterrent to rodents and shrews. More work will be needed to confirm this hypothesis. Whatever the case, safranal does not seem to deter lizards and may even be the initial cue that lures them to the plant in the first place. Tongue flicking was observed in visiting lizards, which is often associated with finding food in other reptiles.

Male flower (a) and female flower (b). Note the presence of the orange glands at the base.

Another interesting observation is that the color of the floral tube and the orange glands within appear to match the colors of one of the lizard pollinators (Pseudocordylus subviridis ). Is it possible that this is further entices the lizards to visit the flowers? Other reptile pollination systems have demonstrated that lizards appear to respond well to color patterns for which they already have some sort of sensory bias. Is it possible that these flowers evolved in response to such a bias? Again, more work will be needed to say for sure.

By excluding vertebrates from visiting the flowers, the team was able to show that indeed lizards appear to be the main pollinators of these plants. Without pollen transfer, seed set is reduced by 95% wheres the additional exclusion of insects only reduced reproductive success by a further 4%. Taken together, it is clear that lizards are the main pollinators of the enigmatic hidden flower. This discovery expands on our limited knowledge of lizard pollination syndromes and rises many interesting questions about how such relationships evolve.

Photo Credit: [1] [2] [3]

Further Reading: [1] [2]

The Upside Down World of Orchid Flowers

Did you know that most orchid flowers you see are actually blooming upside down? That's right, referred to as "resupination," the lower lip of many orchid flowers is actually the top petal and, as the flower develops inside the bud, the whole structure makes a 180° rotation. How and why does this happen?

The lip of an orchid flower usually serves to attract pollinators as well as function as a landing pad for them. The flower of an orchid is an incredibly complex organ with an intriguing evolutionary history. Basically, the lip is the most derived structure on the flower and, in most cases, it is the most important structure in initiating pollination.

The non-resupinate flowers of the grass pink (Calopogon tuberosus) showing the lip on top.

As an orchid flower bud develops, it begins to exhibit gravitropic tendencies, meaning it responds to the pull of gravity. By removing specific floral organs like the column and pollinia, researchers found that they produce special hormones called auxins that tell the developing bud to begin the process of resupination. The ovary starts to twist, causing the flower to stand on its head.

Not all orchids exhibit resupinate flowers. Grass pinks (Calopogon tuberosus) famously bloom with the lip pointing up as it does in the early stages of bud development. It is an interesting mechanism and serves to demonstrate the stepwise tendencies that the forces of natural selection and evolution can manifest. But why does it occur at all? What is the evolutionary advantage of resupinate flowers?

Not only are Dracula flowers resupinate, many species also face them towards the ground.

The most likely answer to this biological twist is that, for orchids, resupination places the lip in such a way that facilitates pollination by whatever the flowers are attracting. For many orchids, this means providing an elaborate landing strip in the form of the lip. For the grass pinks, which operate by slamming visiting bees downward onto the column to achieve pollination, placing the lip at the top makes more mechanical sense. When a bee visits the upward pointing lip thinking it will find a pollen-rich meal, the lip bend at the base like a hinge. Anything goes in evolution provided the genes are present for selection to act upon and nowhere is this fact more beautifully illustrated than in orchids.

Further Reading: [1] [2] [3]

Viper's Bugloss

Photo by Derek Parker licensed under CC BY-NC-ND 2.0

Throughout much of North America, brown fields, roadsides, and other waste places occasionally take on a wonderful blue hue. Often time the cause of this colorful display is none other than Echium vulgare, or as its commonly referred to, viper's bugloss. Viper’s bugloss is a member of the borage family and was originally native to most of Europe and Asia. However, humans introduced it to North America some time ago. It has since naturalized quite well and is even considered invasive in parts of Washington. No matter your views on this plant, the reproductive ecology of this species is quite interesting.

Viper's bugloss produces its flowers on spikes. Starting off pink and gradually changing to blue as they mature, the flowers ripen their male portions on their first day and ripen their female portions on the second day. This is known as "protandry." Plants that exhibit this lifestyle offer researchers a window into the advantages and disadvantages with regards to the fitness investment of each sex. What they have found in viper's bugloss is that there are clearly distinct strategies for each type of flower.

Male flowers are pollinator limited. They must hedge their bets towards increasing the number of visitors. Bees are the main pollinators of this species and the more bees that visit, the more pollen can be disseminated. Unlike female flowers, which are resource limited, male flowers can produce pollen and nectar quite cheaply. Because of this, male flowers produce significantly more nectar than female flowers to bring in more bees. As the anthers senesce and give way to receptive styles, things begin to change. The plant now has to redirect resources into producing seed. At this point, resources are everything. The plant produces considerably less nectar resources than pollen but the bees can’t know that without visiting.

Photo by BLMIdaho licensed under CC BY 2.0

The other interesting aspect its reproductive ecology has to do with population size. Bees are notorious for favoring plants that are more numerous on the landscape. This makes a lot of sense. Why spend time looking for uncommon plants when they can go for easier, more numerous targets. This can be very detrimental to the fitness of rare plant species. However, plants like viper's bugloss don't seem to fall victim to this.

By looking at large and small populations, researchers found that pollination success pretty much evens out for viper's bugloss no matter how numerous it is in a given area. Large populations receive many more visits from bees but the bees spend less time on each flower. When viper's bugloss populations are small, flowers receive fewer visits but bees spend more time at each flower. This results is no significant difference in the reproductive fitness of either population.

Considering how efficient this plant is reproductively, it is no wonder it has done so well outside of its native range. Add to this its ability to grow in some of the worst soil conditions, it goes without saying that viper's bugloss is here to stay. If you find this species growing, certainly take time to get up close with the flowers. You will be glad you did.

Photo Credits: [1] [2]

Further Reading: [1] [2] [3]

Rodents as Pollinators

Leucospermum arenarium in the field and one of its pollinators, Gerbillurus paeba, feeding on flowers. (A) Pollen presenter contact on G. paeba. (B) G. paeba foraging on L. arenarium [Source]

It may come as a surprise to some that small mammals such as rodents, shrews, and even marsupials have been coopted by plants for pollination services. Far from being occasional evolutionary oddities, many plants have coopted small furry critters for their reproductive needs. Some of the best illustrations of this phenomenon occur in the Protea family (Proteaceae).

Protea nana. Photo by SAplants licensed under CC BY-SA 4.0

The various members of Proteaceae are probably best known for their bizarre floral displays. Indeed, they are most often encountered outside of their native habitats as outlandish additions to the cut flower industry. Superficial interest in beauty aside, the floral structure of the various protea genera and species is complex to say the least. They are well adapted to ensure cross pollination regardless of what the inflorescence attracts. Most notable is the fact that pollen doesn’t stay on the anthers. Instead, it is deposited on the tip of a highly modified style, which is referred to as the pollen presenter. Usually these structures remain closed until some visiting animal triggers their release.

The inconspicuous floral display of Protea cordata. Photo by SAplants licensed under CC BY-SA 4.0

Although birds and insects have taken up a majority of the pollination needs of this family, small mammals have entered into the equation on multiple occasions. Pollination by rodents, shrews, and marsupials is collectively referred to as therophilly and it appears to be quite a successful strategy at that. Therophilous pollination has arisen in more than one genera within Proteaceae.

A therophilous pollination syndrome appears to come complete with a host of unique morphological characters aimed at keeping valuable pollen and nectar away from birds and insects. The inflorescences of therophilous species like Protea nana, P. cordata, and Leucospermum arenarium are usually tucked deep inside the branches of these bushes, often at or near ground level. They are also quite robust and sturdy in nature, which is thought to be an adaptation to avoid damage incurred by the teeth of hungry mammals. The inflorescences of therophilous proteas also tend to have brightly colored or even shiny flowers surrounded by inconspicuous brown involucral bracts.

(C) Flowering L. arenarium with dense, mat-forming inflorescences. (D) Geoflorous inflorescences. (E) Pendulous inflorescences above ground level. [Source]

Contrasted against bird pollinated proteas, these inflorescences can seem rather drab but that is because small mammals like rodents and shrews are drawn in by another sense - smell. Therophilous proteas tend to produce inflorescences with strong musty or yeasty odors. They also produce copious amounts of sugar-rich, syrupy nectar. Small mammals, after all, need to take in a lot of calories throughout their waking hours and it appears that proteas use that to their advantage.

A small mouse pollinating Protea nana

As a rodent or shrew slinks in to take a drink, its head gets completely covered in pollen. In fact, they become so dusted with pollen that, before small, easy to hide trail cameras became affordable, pollen loads in the feces of rodents were the main clue that these plants were attracting something other than birds or insects. What’s more, the flowering period of many of these therophilous proteas occurs in the spring, right around the time when many small mammals go into breeding mode. Its during this time that small mammals need all of the energy they can get.

As odd as it may seem, rodent pollination appears to be a successful strategy for a considerable amount of protea species. The proteas aren’t alone either. Other plants appear to have evolved therophilous pollination as well. Nature, after all, works with what it has available and small mammals like rodents make up a considerable portion of regional faunas. With that in mind, it is no wonder that more plants have not converged on a similar strategy. Likely many have, we just need to take the time to sit down and observe.

Photo Credits: [1] [2] [3] [4] [5] [6] [7]

Further Reading: [1] [2] [3] [4] [5]

Toxic Nectar

I was introduced to the concept of toxic nectar thanks to a species of shrub quite familiar to anyone who has spent time in the Appalachian Mountains. Locals will tell you to never place honeybee hives near a patch of rosebay (Rhododendron maximum) for fear of so-called "mad honey." Needless to say, the concept intrigued me.

A quick internet search revealed that this is not a new phenomenon either. Humans have known about toxic nectar for thousands of years. In fact, honey made from feeding bees on species like Rhododendron luteum and R. ponticum has been used more than once during times of war. Hives containing toxic honey would be placed along known routs of Roman soldiers and, after consuming the seemingly innocuous treat, the soldiers would collapse into a stupor only to be slaughtered by armies lying in wait.

Rhododendron luteum. Photo by Chrumps licensed under CC BY 3.0

The presence of toxic nectar seems quite confusing. The primary function of nectar is to serve as a reward for pollinators after all. Why on Earth would a plant pump potentially harmful substances into its flowers?

It is worth mentioning at this point that the Rhododendrons aren't alone. A multitude of plant species produce toxic nectar. The chemicals that make them toxic, though poorly understood, vary almost as much as the plants that make them. Although there have been repeated investigations into this phenomenon, the exact reason(s) remain elusive to this day. Still, research has drummed up some interesting data and many great hypotheses aimed at explaining the patterns.

Catalpa nectar has been shown to deter some ants and butterflies but not large bees. Photo by Le.Loup.Gris licensed under CC BY-SA 3.0

The earliest investigations into toxic nectar gave birth to the pollinator fidelity hypothesis. Researchers realized that meany bees appear to be less sensitive to alkaloids in nectar than are some Lepidopterans. This led to speculation that perhaps some plants pump toxic compounds into their nectar to deter inefficient pollinators, leading to more specialization among pollinating insects that can handle the toxins.

Another hypothesis is the nectar robber hypothesis. This hypothesis is quite similar to the pollinator fidelity hypothesis except that it extends to all organisms that could potentially rob nectar from a flower without providing any pollination services. As such, it is a matter of plant defense.

The nectar of Cyrilla racemiflora is thought to be toxic to some bees. Photo by Koala:Bear licensed under CC BY-SA 2.0

Others feel that toxic nectar may be less about pollinators or nectar robbers and more about microbial activity. Sugary nectar can be a breeding ground for microbes and it is possible that plants pump toxic compounds into their nectar to keep it "fresh." If this is the case, the antimicrobial benefits could outweigh the cost to pollinators that may be harmed or even deterred by the toxic compounds.

Finally, it could be that toxic nectar may have no benefit to the plant whatsoever. Perhaps toxic nectar is simply the result of selection for defense compounds elsewhere in the plant and therefore is expressed in the nectar as a result of pleiotropy. If this is the case then toxic nectar might not be under as strong selection pressures as is overall defense against herbivores. If so, the plants may not be able to control which compounds eventually end up in their nectar. Provided defense against herbivores outweighs any costs imposed by toxic nectar then plants may not have the ability to evolve away from such traits.

Where Spathodea campanulata is invasive, its nectar causes increased mortality in native bee hives. Photo by mauro halpern licensed under CC BY 2.0

So, where does the science land us with these hypotheses? Do the data support any of these theories? This is where things get cloudy. Despite plenty of interest, evidence in support of the various hypotheses is scant. Some experiments have shown that indeed, when given a choice, some bees prefer non-toxic to toxic nectar. Also, toxic nectar appears to dissuade some ants from visiting flowers, however, just as many experiments have demonstrated no discernible effect on bees or ants. What's more, at least one investigation found that the amount of toxic compounds within the nectar of certain species varies significantly from population to population. What this means for pollination is anyone's' guess.

It is worth noting that most of the pollination-related hypotheses about toxic nectar have been tested using honeybees. Because they are generalist pollinators, there could be something to be said about toxic nectar deterring generalist pollinators in favor of specialist pollinators. Still, these experiments have largely been done in regions where honeybees are not native and therefore do not represent natural conditions.

Simply put, it is still too early to say whether toxic nectar is adaptive or not. It could very well be that it does not impose enough of a negative effect on plant fitness to evolve away from. More work is certainly needed. So, if you are someone looking for an excellent thesis project, here is a great opportunity. In the mean time, do yourself a favor and don't eat any mad honey.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3] [4] [5] [6]

The Trumpet Creeper

Photo by beautifulcataya licensed under CC BY-NC-ND 2.0

With its impressive bulk and those stunning tubular red flowers, one would be excused for thinking that the trumpet creeper (Campsis radicans) was a tropical vine. Indeed, the family to which it belongs, Bignoniaceae, is largely tropical in its distribution. There are a handful of temperate representatives, however, and the trumpet creeper is one of the most popular. Its beauty aside, this plant is absolutely fascinating.

As many of you probably know, the trumpet creeper can reach massive proportions. In the garden, this can often result in collapsed structures as its weight and speed of growth is something few adequately prepare for. In the wild, I most often see this vine in somewhat disturbed forests, usually near a floodplain. As such, it is supremely adapted to take a hit and keep on growing year after year.

Photo by Maja Dumat licensed under CC BY 2.0

One of the many reasons this plant performs so well both where it is native and where it is not is that it recruits body guards. This is easy to witness in a garden setting as the branches and especially the flowers are frequently crawling with ants. Trumpet creepers trade food for protection via specialized organs called extrafloral nectaries. These structures secrete sugary nectar that is readily sucked up by tenacious ants. When a worker ant finds a vine, more workers are soon to follow. 

Amazingly for a temperate plant, trumpet creepers produce more extrafloral nectaries of all four categories - petiole, calyx, corolla, and fruit. What this means is that all of the important organs are covered in insects that viciously attack anything that might threaten this sugary food supply. Hassle one of these vines at your own peril. With its photosynthetic and reproductive structures protected, trumpet creepers make a nice living once established.

Photo by Salicyna licensed under CC BY-SA 4.0

Reproduction is another fascinating aspect of trumpet creeper biology. A closer inspection of the floral anatomy will reveal a bilobed stigma. Amazingly, this stigma has the ability to open and close as potential pollinators visit the flowers. Stigmatic movement in the trumpet creeper has attracted a bit of attention from researchers over the years. What is its function?

Evidence suggests that the opening and closing of the lobed stigma is way of increasing the chances of pollination. Touch alone is not enough to trigger the movement. However, when researchers dusted pollen onto the stigma, then it began to close. What's more, this action happens within 15 to 60 seconds. Amazingly, there appears to be a threshold to whether the stigma stays closed or reopens after 3 hours or so.

Photo by Jim Conrad (Public Domain)

It turns out, the threshold seems to depend on the amount of pollen being deposited. Only after 350 grains found their way onto the stigma did it close permanently. Experts feel that this a means by which the plant ensured ample seed set. If too few pollen grains end up on the stigma, the plant risks not having all of its ovules fertilized. By permanently closing after enough pollen grains are present, the plant can ensure that the pollen grains can germinate and fertilize the ovules without being brushed off.

It is interesting to note that the flowers frequently remain on the plant after they have been fertilized. This likely serves to maintain a largely floral display that continues to attract pollinators until most of the flowers have been pollinated. Speaking of pollinators, observations have revealed that the trumpet creeper is pollinated primarily by ruby-throated hummingbirds. Although insects like bumblebees frequently visit these blooms, bringing pollen with them in the process, hummingbirds, on average, bring and deposit 10 times as much pollen as any other visitor. And, considering the threshold on pollen mentioned above, trumpet creeper appears to have evolved a pollination syndrome with these lovely little birds.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3] [4]

How Aroids Turn Up the Heat

Photo by Jörg Hempel licensed under CC BY-SA 2.0

A subset of plants have evolved the ability to produce heat, a fact that may come as a surprise to many reading this. The undisputed champions of botanical thermogenesis are the aroids (Araceae). Exactly why they do so is still the subject of scientific debate but the means by which heat is produced is absolutely fascinating.

The heat producing organ of an aroid is called the spadix. Technically speaking, a spadix is a spike of minute flowers closely arranged around a fleshy axis. All aroid inflorescences have one and they come in a wide variety of shapes, colors, and textures. To produce heat, the spadix is hooked up to a massive underground energy reserve largely in the form of carbohydrates or sugars. The process of turning these sugars into heat is rather complex and surprisingly animal-like.

Cross section of a typical aroid inflorescence with half of the protective spathe removed. The spadix is situated in the middle with a rings of protective hairs (top), male flowers (middle), and female flowers (bottom). Photo by Kristian Peters -- Fabelfroh licensed under CC BY-SA 3.0

It all starts with a compound we are rather familiar with - salicylic acid - as it is the main ingredient in Aspirin. In aroids, however, salicylic acid acts as a hormone whose job it is to initiate both the heating process as well as the production of floral scents. It signals the mitochondria packed inside a ring of sterile flowers located at the base of the spadix to change their metabolic pathway.

In lieu of their normal metabolic pathway, which ends in the production of ATP, the mitochondria switch over to a pathway called the "Alternative Oxidase Metabolic Pathway." When this happens, the mitochondria start burning sugars using oxygen as a fuel source. This form of respiration produces heat.

Thermal imaging of the inflorescence of Arum maculatum.

As you can imagine, this can be a costly process for plants to undergo. A lot of energy is consumed as the inflorescence heats up. Nonetheless, some aroids can maintain this costly level of respiration intermittently for weeks on end. Take the charismatic skunk cabbage (Symplocarpus foetidus) for example. Its spadix can reach temperatures of upwards of 45 °F (7 °C) on and and off for as long as two weeks. Even more incredible, the plant is able to do this despite freezing ambient temperatures, literally melting its way through layers of snow.

For some aroids, however, carbohydrates just don't cut it. Species like the Brazilian Philodendron bipinnatifidum produce a staggering amount of floral heat and to do so requires a different fuel source - fat. Fats are not a common component of plant metabolisms. Plants simply have less energy requirements than most animals. Still, this wonderful aroid has converged on a fat-burning metabolic pathway that puts many animals to shame. 

The inflorescence of Philodendron bipinnatifidum can reach temps as high as 115 °F (46 °C). Photo by Tekwani licensed under CC BY-SA 3.0

P. bipinnatifidum stores lots of fat in sterile male flowers that are situated between the fertile male and female flowers near the base of the spadix. As soon as the protective spathe opens, the spadix bursts into metabolic action. As the sun starts to set and P. bipinnatifidum's scarab beetle pollinators begin to wake up, heat production starts to hit a crescendo. For about 20 to 40 minutes, the inflorescence of P. bipinnatifidum reaches temperatures as high as 95 °F (35 °C) with one record breaker maxing out at 115 °F (46 °C)! Amazingly, this process is repeated again the following night.

It goes without saying that burning fat at a rate fast enough to reach such temperatures requires a lot of oxygen. Amazingly, for the two nights it is in bloom, the P. bipinnatifidum inflorescence consumes oxygen at a rate comparable to that of a flying hummingbird, which are some of the most metabolically active animals on Earth.

The world's largest inflorescence belongs to the titan arum (Amorphophallus titanum) and it too produces heat. Photo by Fbianh licensed under CC0 1.0

Again, why these plants go through the effort of heating their reproductive structures is still a bit of a mystery. For most, heat likely plays a role in helping to volatilize floral scents. Anyone that has spent time around blooming aroids knows that this plant family produces a wide range of odors from sweet and spicy to downright offensive. By warming these compounds, the plant may be helping to lure in pollinators from a greater distance away. It is also thought that the heat may be an attractant in and of itself. This is especially true for temperate species like the aforementioned skunk cabbage, which frequently bloom during colder months of the year. Likely both play a role to one degree or another throughout the aroid family.

What we can say is that the process of plant thermogenesis is absolutely fascinating and well worth deeper investigation. We still have much to learn about this charismatic group of plants.

LEARN MORE ABOUT AROID POLLINATION HERE



Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3] [4] [5] [6] [7] [8]

Pollen Competition

Photo by Martin LaBar licensed under CC BY-NC 2.0

The animal kingdom is rife with sexual conflict. We are all aware of what is going on when two stag deer lock antlers or when a group of male sage grouse flaunt themselves on leks as females look on. But what about plants? Is there sexual conflict among plant species? Whether pollen ends up on a stigma via wind or animal, is there any way for a plant to "choose" who gets to fertilize the ovule?

It turns out, yes, there is. Sexual competition is part of the pollination process. In fact, some of the most familiar floral morphologies may have evolved as a way of weeding out weak paternal lines. To understand this process better, though, we must first quickly review exactly what goes on during pollination.

Photo by Nick Fedele licensed under CC BY-NC-SA 2.0

Pollen is a male gamete. Each grain is haploid and contains only a single copy of a plant’s chromosomes. When a pollen grain lands on a stigma, the grain germinates like a tiny seed, sending down a root-like growth called a pollen tube. This tube grows down into the ovary until it finds an unfertilized ovule. At this point, sperm travels down the pollen tube where it can unite with the ovule, thus forming a seed.

By CNX OpenStax licensed under CC BY 4.0

It’s the formation of this pollen tube that introduces the idea of competition among pollen grains. Again, whether by wind or animal, the pollen arriving to a new plant generally doesn't come from a single individual. Pollen from many potential paternal lines can arrive all at once. As such, the race to fertilize the ovules can be quite intense, and this is where competition begins.

Remember, pollen only contains a single set of chromosomes from the parent plant, thus all alleles, both functioning and deleterious, are represented. During the growth of the pollen tube, upwards of 60% of the pollen genome is actively transcribed. Any pollen containing lots of deleterious alleles is going to have a much harder time competing with pollen grains that have fewer deleterious alleles. Their tubes have a harder time making it to the ovules in time to fertilize them.

Photo by Dartmouth Electron Microscope Facility, Dartmouth College

It is thought that the length of the style (the stem connecting the stigma to the ovaries) may also provide a sort of "proving ground" for pollen too. For instance, picture the flowers of a lily or a mallow. Those long, slender styles may actually be acting like a race track. Only the pollen with the best selection of genetic material will be able to grow their pollen tubes fast enough to reach the ovules, leaving the weaker competition in the dust. In this way, plants may actually be sorting out stronger paternal lines, which makes sense for sessile organisms that can't see.

As with everything in nature, there is far more nuance to this than what I have outlined above. Much work is being done to test some of the earlier assumptions and data surrounding this concept of pollen competition. It certainly happens but the degree to which any given species utilizes such methods is up for debate. Still, it paints a much more interesting picture of mate selection in plants. Static, plants are not!

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3] [4] [5] [6] [7]

The Intriguing Pollination of a Central American Anthurium

As an avid gardener of both indoors and out, there are few better experiences than getting to see familiar plants growing in the wild for the first time. That experience is made all the better when you find out new and interesting facts about their ecology. On a recent trip to Costa Rica, I was introduced to a wide variety of Anthurium species. I marveled at how amazing these plants look in situ and was taken aback to learn that many produce flowers with intoxicating aromas.

I was also extremely fortunate to be in the presence of some aroid experts during this trip and their knowledge fueled my interest in getting up close and personal with what little time I had with these plants. They were able to ID the plants and introduce me to their biology. One species in particular has been the subject of interest in an ongoing pollination study that has proven to be unique.

The plant in question is known scientifically as Anthurium acutifolium and it is rather charming once you get to know it. It is a terrestrial plant with relatively large leaves for its overall size. Its range includes portions of lowland Costa Rica and Panama. Its flowers are typical of what one would expect out of this family. They are fused into a type of inflorescence known as a spadix and can range in color from white to green and occasionally red. If you are lucky to visit the spadix between roughly 8:00 AM and 12:30 PM, you may notice a rich scent that, to me, is impossible to describe in words.

It's this scent that sets the stage for pollination in this species. During some down time, University of Vienna grad student Florian Etl discovered that the spadix of A. acutifolium was getting a lot of attention from a particular species of small bee. Closer inspection revealed that they were all males of a species of oil-collecting bee known as Paratetrapedia chocoensis. Now, the females of these oil collecting bees are well known in the pollination literature. They visit flowers that secrete special oils that the females then use to build nests and feed their young. This is why the attention from male bees was so intriguing.

A: A male P. chocoensis bee approaching a scented spadix of an inflorescence of A. acutifolium. B: The abdominal mopping behavior of male P. chocoensis oil bees on a spadix. C: Ventral side of the abdomen of a male P.chocoensis covered with pollen. D: A male P. chocoensis bee on a spadix of an inflorescence of A. acutifolium, touching the pollen shedding anthers. E: Pubescent region pressed on the surface of A. acutifolium during the mopping behavior. F: A scented inflorescence of A. acutifolium with three male P. chocoensis individuals. G: Image of the abdomen of a male P.chocensis in lateral view showing the conspicuous pubescent region. (SOURCE)

Males would land on the spadix and begin rubbing the bottom of their abdomen along its surface. In doing so, they inevitably picked up and deposited pollen. To date, such behavior was unknown among male oil bees. What exactly were these male bees up to?

As it turns out, the males were collecting fragrances. Close inspection of their morphology revealed that each male has a small patch of dense hairs underneath their abdomen. The males are definitely not after fatty oils or nectar as A. acutifolium does not secrete either of these substances. Instead, it would appear that the male oil bees are there to collect scent, which is mopped up by that dense patch of hairs. Even more remarkable is the fact that in order to properly collect these fragrance compounds, the bees are likely using solvents that they have collected from other flowering plant species around the forest.

What they are doing with these scent compounds remains a mystery but some potential clues lie in another scent/pollination system. Male orchid bees perform similar scent-collecting activities in order to procure unique scent bouquets. Though the exact function of their scent collecting is not known either, we do know that these scents are used in the process of finding and procuring mates. It is likely that these male oil bees are using them in a similar way.

Taken together, these data suggest that a very specific pollination syndrome involving A. acutifolium and male oil bees has evolved in Central American forests. No other insects were observed visiting the flowers of A. acutifolium and the scents only ever attracted males of these specific oil bees during the hours in which the spadix was actively producing the compounds. This is a remarkable pollination syndrome and one that encourages us to start looking elsewhere in the forest. This, my friends, is why there is no substitute for simply taking the time to observe nature. We must take the time to get outside and poke around because we stand to miss out on so much of what makes our world tick and without such knowledge, we risk losing so much. 

Photo Credits: Florian Etl [1]

Further Reading: [1]

Daffodil Insights

Photo by Amanda Slater licensed under CC BY-SA 2.0

Daffodils seem to be everywhere. Their horticultural popularity means that, for many of us, these plants are among the first flowers we see each spring. Daffodils are so commonplace that it's as if they evolved to live in our gardens and nowhere else. Indeed, daffodils have had a long, long history with human civilization, so much so that it is hard to say when our species first started to cohabitate. Our familiarity with these plants belies an intriguing natural history. What follows is a brief overview of the world of daffodils. 

If you are like me, then you may have gone through most of your life not noticing much difference between garden variety daffodils. Though many of us will be familiar with only a handful of daffodil species and cultivars, these introductions barely scratch the surface. One may be surprised to learn that as of 2008, more than 28,000 daffodil varieties have been named and that number continues to grow each and every year. Even outside of the garden, there is some serious debate over the number of daffodil species, much of this having to do with what constitutes a species in this group.

Narcissus poeticus

As I write this, all daffodils fall under the genus Narcissus. Estimates as to the number of species within Narcissus range from as few as 50 to as many as 80. The genus itself sits within the family Amaryllidaceae and is believed to have originated somewhere between the late Oligocene and early Miocene, some 18 to 30 million years ago. Despite its current global distribution, Narcissus are largely Mediterranean plants, with peak diversity occurring on the Iberian Peninsula. However, thanks to the aforementioned long and complicated history in cultivation, it has become quite difficult to understand the full range of diversity in form and habitat of many species. To understand this, we first need to understand a bit about their reproductive habits.

Much of the evolution of Narcissus seems to center around floral morphology and geographic isolation. More specifically, the length of the floral tube or "corona" and the position of the sexual organs within, dictates just who can effectively pollinate these plants. The corona itself is not made up of petals or sepals but instead, its tube-like appearance is due to a fusion of the stamens into the famous trumpet-like tube we know and love.

Variation in corona shape and size has led to the evolution of three major pollination strategies within this genus. The first form is the daffodil form, whose stigma is situated at the mouth of the corolla, well beyond the 6 anthers. This form is largely pollinated by larger bees. The second form is the paperwhite form, whose stigma is situated more closely to or completely below the anthers at the mouth of the corona. This form is largely pollinated by various Lepidoptera as well as long tongued bees and flies. The third form is the triandrus form, which exhibits three distinct variations on stigma and anther length, all of which are situated deep within the long, narrow corona. The pendant presentation of the flowers in this group is thought to restrict various butterflies and moths from entering the flower in favor of bees.

Narcissus tazetta. Photo by Fanghong licensed under CC BY-SA 3.0

The variations on these themes has led to much reproductive isolation among various Narcissus populations. Plants that enable one type of pollinator usually do so at the exclusion of others. Reproductive isolation plus geographic isolation brought on by differences in soil types, habitat types, and altitudinal preferences is thought to have led to a rapid radiation of these plants across the Mediterranean. All of this has gotten extremely complicated ever since humans first took a fancy to these bulbs.

Narcissus cyclamineus. Photo by Francine Riez licensed under CC BY-SA 3.0

Reproductive isolation is not perfect in these plants and natural hybrid zones do exist where the ranges of two species overlap. However, hybridization is made much easier with the helping hand of humans. Whether via landscape disturbance or direct intervention, human activity has caused an uptick in Narcissus hybridization. For centuries, we have been mixing these plants and moving them around with little to no record as to where they originated. What's more, populations frequently thought of as native are actually nothing more than naturalized individuals from ancient, long-forgotten introductions. For instance, Narcissus populations in places like China, Japan, and even Great Britain originated in this manner.

All of this mixing, matching, and hybridizing lends to some serious difficulty in delineating species boundaries. It would totally be within the bounds of reason to ask if some of the what we think of as species represent true species or simply geographic varieties on the path to further speciation. This, however, is largely speculative and will require much deeper dives into Narcissus phylogenetics.

Narcissus triandrus. Photo by Dave Gough licensed under CC BY 2.0

Despite all of the confusion surrounding accurate Narcissus taxonomy, there are in fact plenty of true species worth getting to know. These range in form and habit far more than one would expect from horticulture. There are large Narcissus and small Narcissus. There are Narcissus with yellow flowers and Narcissus with white flowers. Some species produce upright flowers and some produce pendant flowers. There are even a handful of fall-blooming Narcissus. The variety of this genus is staggering if you are not prepared for it.

Narcissus viridiflorus - a green, fall-blooming daffodil. Photo by A. Barra licensed under CC BY 3.0

After pollination, the various Narcissus employ a seed dispersal strategy that doesn't get talked about enough in reference to this group. Attached to each hard, black seed are fatty structures known as eliasomes. Eliasomes attract ants. Like many spring flowering plant species around the globe, Narcissus utilize ants as seed dispersers. Ants pick up the seeds and bring them back to their nests. They go about removing the eliasomes and then discard the seed. The seed, safely tucked away in a nutrient-rich ant midden, has a much higher chance of germination and survival than if things were left up to simple chance. It remains to be seen whether or not Narcissus obtain similar seed dispersal benefits from ants outside of their native range. Certainly Narcissus populations persist and naturalize readily, however, I am not aware if ants have any part in the matter.

The endangered Narcissus alcaracensis. Photo by José Luis López González licensed under CC BY-SA 4.0

Despite their popularity in the garden, many Narcissus are having a hard go of it in the wild. Habitat destruction, climate change, and rampant collecting of wild bulbs are having serious impacts on Narcissus numbers. The IUCN considered at least 5 species to be endangered and a handful of some of the smaller species already thought to be extinct in the wild. In response to some of these issues, protected areas have been established that encompass at least some of the healthy populations that remain for some of these species.

If you are anything like me, you have ignored Narcissus for far too long. Sure, they aren't native to the continent on which I live, and sure, they are one of the most commonly used plants in a garden setting, but every species has a story to tell. I hope that, armed with this new knowledge, you at least take a second look at the Narcissus popping up around your neighborhood. More importantly, I hope this introduction makes you appreciate their wild origins and the fact that we still have much to learn about these plants. I have barely scratched the surface of this genus and there is more more information out there worth perusing. Finally, I hope we can do better for the wild progenitors of our favorite garden plants. They need all the help they can get and unless we start speaking up and working to preserve wild spaces, all that will remain are what we have in our gardens and that is not a future I want to be a part of.

Photo Credits: [1] [2] [3] [4] [5] [6] [7]

Further Reading: [1] [2] [3] [4] [5] [6] [7] [8] [9]

Do Yeasts Aid Pollination For the Stinking Hellebore?

Photo by Mark Gurney licensed under CC BY-NC-SA 2.0

Whether they are growing in their native habitat or in some far away garden, Hellebores are some of the earliest plants to bloom in the spring. Hellebore flowers can often be seen blooming long before the snow has melted away. All early blooming plant species are faced with the challenge of attracting pollinators. Though the competition for insect attention is minimal among these early bloomers, only the hardiest insects are out and about on cold, dreary days. It stands to reason then that anything that can entice a potential pollinator would be of great benefit for a plant.

That is why the presence of yeast in the nectar of at least one species of Hellebore has attracted the attention of scientists. The species in question is known scientifically as Helleborus foetidus. The lack of appeal in its binomial is nothing compared to its various common names. One can often find H. foetidus for sale under names like the "stinking hellebore" or worse, "dungwort." All of these have to do with the unpleasant aroma given off by its flowers and bruised foliage. Surprisingly, that is not the topic of this post.

Photo by Bernd Haynold licensed under CC BY-SA 3.0

What is more intriguing about the flowers of H. foetidus is that the nectar produced by its smelly green flowers harbors dense colonies of yeast. Yeasts are everywhere on this planet and despite their economic importance, little is known about how they function in nature. For instance, what the heck are these yeast colonies doing in the nectar of this odd Hellebore?

To test this, two researchers from the Spanish National Research Council manipulated yeast colonies within the flowers to see what might be happening. It turns out, yeast in the nectar of H. foetidus actually warms the flowers. As the yeast feed on the sugars within the nectar, their metabolic activity can raise the temperature of the flowers upwards of 2 °C above the ambient. As far as we know, the only other ways in which floral heating has been achieved is either via specific metabolic processes within the floral tissues or by direct heating from the sun. 

In heating the flowers, these yeast colonies may be having serious impacts on the reproductive success of H. foetidus. For starters, these plants are most at home under the forest canopies of central and western Europe. What's more, many populations find themselves growing in the dense shade of evergreens. This completely rules out the ability to utilize solar energy to heat blooms. Additionally, floral heat can mean more visits by potential pollinators. Experiments have shown that bees preferentially visit flowers that are slightly warmer than ambient temperatures. Even the flowers themselves can benefit from that heat. Warmer flowers have higher pollination rates and better seed set.

Bombus terrestris was one of the most common floral visitors of Helleborus foetidus. Photo by Vera Buhl licensed under CC BY-SA 3.0

Yeast colonies also have their downsides. The heat generated by the yeast comes from the digestion of sugars. Indeed, nectar housing yeast colonies had drastically reduced sugar loads than nectar without yeast. This has the potential to offset many of the benefits of floral warming in large part because bees are good at discriminating. Bees are visiting these blooms as a food source and by diminishing the sugar content of the nectar, the yeast may be turning bees off to this potential source. The question then becomes, do bees prefer heat over sugar-rich food? The authors think there might be a trade-off, with bees preferring heated flowers on colder days and sugar-rich flowers on warmer days.

Helleborus foetidus flowering before the snow has had a chance to melt!

Though the authors found evidence for heating, they did not test for pollinator preference. All we know at this point is that yeast in the nectar significantly warms H. foetidus flowers. Since this piece was originally published, more attention has been paid to the benefits of the heat generated from yeast. Interestingly, researchers found that pollen tube formation was higher for H. foetidus flowers that experienced heat earlier in the season but not for those that experienced heat later on. This response, however, was not due to the warming directly. Instead, it had more to do with bee preference.

As it turns out, bumblebees do in fact prefer to visit heated flowers but their preference is limited to the early periods of flowering when ambient temperatures are still quite low. More bumblebees visiting heated flowers in the early spring equated to more pollen being deposited on the stigma, which in turn led to an increase in pollen tube formation and higher seed set. Later on in the season, when ambient temperatures increased a bit, this positive effect dropped off as bees apparently spent more time foraging elsewhere.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3]

From Herbivore to Pollinator Thanks to a Parasitoid

In the Atlantic forests of Brazil resides a small orchid known scientifically as Dichaea cogniauxiana. Like most plant species, this orchid experiences plenty of pressure from herbivores. It faces rather intense pressures from two species of weevil in the genus Montella. These weevils are new to science and have yet been given full species status. What's more, they don't appear to eat the leaves of D. cogniauxiana. Instead, female weevils lay eggs in the developing fruits and the larvae hatch out and consume the seeds within. In other words, they treat the fruits like a nursery chamber.

This is where this relationship gets interesting. You see, the weevils themselves appear to take matters into their own hands. Instead of waiting to find already pollinated orchids, an event that can be exceedingly rare in these dense forests, these weevils go about pollinating the orchids themselves. Females have been observed picking up orchid pollinia and depositing the pollen onto the stigmas. In this way, they ensure that there will be developing fruits in which they can raise their young.

Left unchecked, the weevil larvae readily consume all of the developing seeds within the pod, an unfortunate blow to the reproductive efforts of this tiny orchid. However, the situation changes when parasitoid wasps enter the mix. The wasps are also looking for a place to rear their young but the wasp larvae do not eat orchid seeds. Instead, the wasps must find juicy weevil larvae in which to lay their eggs. When the wasp larvae hatch out, they eat the weevil larvae from the inside out and this is where things get really interesting.

The wasp larvae develop at a much faster rate than do the weevil larvae. As such, they kill the weevil long before it has a chance to eat all of the orchid seeds. By doing so, the wasp has effectively rescued the orchids reproductive effort. Over a five year period, researchers based out of the University of Campinas found that orchid fruits in which wasp larvae have killed off the weevil larvae produced nearly as many seeds as uninfected fruits. As such, the parasitoid wasps have made effective pollinators out of otherwise destructive herbivorous weevils.

The fact that a third party (in this case a parasitic wasp) can change a herbivore into an effective pollinator is quite remarkable to say the least. It reminds us just how little we know about the intricate ways in which species interact and form communities. The authors note that even though pollination in this case represents selfing and thus reduced genetic diversity, it nonetheless increases the reproductive success of an orchid that naturally experiences low pollination rates to begin with. In the hyper diverse and competitive world of Brazilian rainforests, even self-pollination cab be a boost for this orchid.

Photo Credits: [1] [2]

Further Reading: [1]

An Endangered Iris With An Intriguing Pollination Syndrome

The Golan iris (Iris hermona) is a member of the Oncocyclus section, an elite group of 32 Iris species native to the Fertile Crescent region of southwestern Asia. They are some of the showiest irises on the planet. Sadly, like many others in this section, the Golan iris is in real danger of going extinct.

The Golan iris has a rather limited distribution. Despite being named in honor of Mt. Hermon, it is restricted to the Golan Heights region of northern Israel and southwestern Syria. Part of the confusion stems from the fact that the Golan iris has suffered from a bit of taxonomic uncertainty ever since it was discovered. It is similar in appearance to both I. westii and I. bismarckiana with which it is frequently confused. In fact, some authors still consider I. hermona to be a variety of I. bismarckiana. This has led to some serious issues when trying to assess population numbers. Despite the confusion, there are some important anatomical differences between these plants, including the morphology of their rhizomes and the development of their leaves. Regardless, if these plants are in fact different species, it means their respective numbers in the wild decrease dramatically. 

Photo by Dr. Avishai Teicher Pikiwiki Israel licensed under CC BY 2.5

Like other members of the Oncocyclus group, the Golan iris exhibits an intriguing pollination syndrome with a group of bees in the genus Eucera. Their large, showy flowers may look like a boon for pollinators, however, close observation tells a different story. The Golan iris and its relatives receive surprisingly little attention from most of the potential pollinators in this region.

One reason for their lack of popularity has to do with the rewards (or lack thereof) they offer potential visitors. These irises produce no nectar and very little pollen. Because of this and their showy appearance, most pollinators quickly learn that these plants are not worth the effort. Instead, the only insects that ever pay these large blossoms any attention are male Eucerine bees. These bees aren't looking for food or fragrance, however. Instead, they are looking for a place to rest. 

A Eucerine bee visiting a nectar source. Photo by Gideon Pisanty (Gidip) גדעון פיזנטי • CC BY 3.0

The Oncocyclus irises cannot self pollinate, which makes studying potential pollinators a bit easier. During a 5 year period, researchers noted that male Eucerine bees were the only insects that regularly visited the flowers and only after their visits did the plants set seed. The bees would arrive at the flowers around dusk and poke around until they found one to their liking. At that point they would crawl down into the floral tube and would not leave again until morning. The anatomy of the flower is such that the bees inevitably contact stamen and stigma in the process. Their resting behavior is repeated night after night until the end of the flowering season and in this way pollination is achieved. Researchers now believe that the Golan iris and its relatives are pollinated solely by these sleeping male bees.

Sadly, the status of the Golan iris is rather bleak. As recent as the year 2000, there were an estimated 2,000 Golan irises in the wild. Today that number has been reduced to a meager 350 individuals. Though there is no single smoking gun to explain this precipitous decline, climate change, cattle grazing, poaching, and military activity have exacted a serious toll on this species. Plants are especially vulnerable during drought years. Individuals stressed by the lack of water succumb to increased pressure from insects and other pests. Vineyards have seen an uptick in Golan in recent years as well, gobbling up viable habitat in the process.

Photo by Dr. Avishai Teicher Pikiwiki Israel licensed under CC BY 2.5

It is extremely tragic to note that some of the largest remaining populations of Golan irises can be found growing in active mine fields. It would seem that one of the only safe places for these endangered plants to grow are places that are extremely lethal to humans. It would seem that our propensity for violent tribalism has unwittingly led to the preservation of this species for the time being.

At the very least, some work is being done not only to understand what these plants need in order to germinate and survive, but also assess the viability of relocated plants that are threatened by human development. Attempts at transplanting individuals in the past have been met with limited success but thankfully the Oncocyclus irises have caught the eye of bulb growers around the world. By sharing information on the needs of these plants in cultivation, growers can help expand on efforts to save species like the Golan iris.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3] [4]

California Bumblebee Decline Linked to Feral Honeybees

Photo by Alvesgaspar licensed under CC BY-SA 3.0

Worldwide, pollinators are having a rough go of it. Humans have altered the landscape to such a degree that many species simply can't keep up. The proverbial poster child for pollinator issues is the honeybee (Apis mellifera). As a result, countless native pollinators get the short shrift when it comes to media attention. This isn't good because outside of intense industrial agriculture, native pollinators make up the bulk of pollination services. Similarly, honeybee fandom often overshadows any potential negative effects these introduced insects might be having on native pollinators.

Long term scientific investigations are starting to paint a more nuanced picture of the impact introduced honeybees are having on native ecosystems. For instance, research based out of California is finding that honeybees are playing a big role in the decline of native bumblebee populations. What's more, these negative impacts are only made worse in the light of climate change.

Licensed under public domain

For over 15 years, ecologist Dr. Diane Thompson has been studying bumblebee populations in central California. At no point during those early years did any of the bumblebee species she focuses on show signs of decline. In fact, they were quite common. Then, around the year 2000, feral honeybees started to establish themselves in the area. Honeybee colonies were becoming more and more numerous each and every year and that is when she started noticing changes in bumblebee behavior and numbers.

You see, honeybees are extremely successful foragers. They are generalists, which means they can visit a wide variety of flower types. As a result, they are extremely good at competing for floral resources compared to native bumblebees. Her results show that increases in the number of honeybee colonies caused not only a reduction in foraging among the native bumblebees, they also caused a reduction in bumblebee colony success. The native bumblebees simply weren't raising as many young as they were before honeybees entered the system.

Decreased rainfall cause a decline in flower densities of Scrophularia californica, a key resource for native bumblebees in this system. Photo by USFWS - Pacific Region licensed under CC BY-NC 2.0

Climate change is only making things worse. As drought years become not only more severe but also more intense, the amount of flowers available during the growing season also declines. With fewer flowers on the landscape, bumblebees and honeybees are forced into closer proximity for foraging and the clear winner in most foraging disputes are the tenacious honeybees. As such, bumblebees are chased off the already diminishing floral displays. By 2014, Dr. Thompson had quantified a significant decline in native bumblebee populations as a result.

It would be all too convenient to say that this research represents an isolated case. It does not. More and more research is finding that honeybees frequently out-compete native pollinators for resources such as food and nesting sites. Such effects are especially pronounced in rapidly changing ecosystems. Although honeybees are here to stay, it is important that we realize the impacts that these feral insects are having on our native ecosystems and begin to better appreciate and facilitate the services provided by our native pollinators. 

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3] [4]

On the Ecology of Krameria

Photo by Stan Shebs licensed under CC BY-SA 3.0

There is something satisfying about saying "Krameria." Whereas so many scientific names act as tongue twisters, Krameria rolls of the tongue with a satisfying confidence. What's more, the 18 or so species within this genus are fascinating plants whose lifestyles are as exciting as their overall appearance. Today I would like to give you an overview of these unique parasitic plants.

Commonly known as rhatany, these plants belong to the family Krameriaceae. This is a monotypic clade, containing only the genus Krameria. Historically there has been a bit of confusion as to where these plants fit on the tree of life. Throughout the years, Krameria has been placed in families like Fabaceae and Polygalaceae, however, more recent genetic work suggests it to be unique enough to warrant a family status of its own. 

Regardless of its taxonomic affiliation, Krameria is a wonderfully specialized genus of plants with plenty of offer the biologically curious among us. All 18 species are shrubby, though at least a couple species can sometimes barely qualify as such. They are a Western Hemisphere taxon with species growing native as far south as Paraguay and Chile and as far north as Kansas and Colorado. They generally inhabit dry habitats.

Photo by Stan Shebs licensed under CC BY-SA 3.0

As I briefly mentioned above, most if not all of the 18 species are parasitic in nature. They are what we call "hemiparasites" in that despite stealing from their hosts, they are nonetheless fully capable of photosynthesis. It is interesting to note that no one (from what I have been able to find) has yet been able to raise these plants in captivity without a host. It would seem that despite being able to photosynthesize, these plants are rather specialized parasites. 

That is not to say that they have evolved to live off of a specific host. Far from it actually. A wide array of potential hosts, ranging from annuals to perennials, have been identified. What I find most remarkable about their parasitic lifestyle is the undeniable advantage it gives these shrubs in hot, dry environments. Research has found that despite getting a slow start on growing in spring, the various Krameria species are capable of performing photosynthesis during extremely stressful periods and for a much longer duration than the surrounding vegetation. 

Photo by mlhradio licensed under CC BY-NC 2.0

The reason for this has everything to do with their parasitic lifestyle. Instead of producing a long taproot to reach water reserves deep in the soil, these shrubs invest in a dense layer of lateral roots that spread out in the uppermost layers of soil seeking unsuspecting hosts. When these roots find a plant worth parasitizing, they grow around its roots and begin taking up water and nutrients from them. By doing this, Krameria are not limited by what water or other resources their roots can find in the soil. Instead, they have managed to tap into large reserves that would otherwise be locked away inside the tissues of their neighbors. As such, the Krameria do not have to worry about water stress in the same way that non-parasitic plants do. 

Photo by Stan Shebs licensed under CC BY-SA 3.0

By far the most stunning feature of the genus Krameria are the flowers. Looking at them it is no wonder why they have been associated with legumes and milkworts. They are beautiful and complex structures with a rather specific pollination syndrome. Krameria flowers produce no nectar to speak of. Instead, they have evolved alongside a group of oil-collecting bees in the genus Centris.

One distinguishing feature of Krameria flowers are a pair of waxy glands situated on each side of the ovary. These glands produce oils that female Centris bees require for reproduction. Though Centris bees are not specialized on Krameria flowers, they nonetheless visit them in high numbers. Females alight on the lip and begin scraping off oils from the glands. As they do this, they inevitably come into contact with the stamens and pistil. The female bees don't feed on these oils. Instead, they combine it with pollen and nectar from other plant species into nutrient-rich food packets that they feed to their developing larvae.  

Photo by João Medeiros licensed under CC BY 2.0

Following fertilization, seeds mature inside of spiny capsules. These capsules vary quite a bit in form and are quite useful in species identification. Each spine is usually tipped in backward-facing barbs, making them excellent hitchhikers on the fur and feathers of any animal that comes into contact with them.  

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3] [4]

The Traveler's Palm

© CEphoto, Uwe Aranas licensed under CC BY-SA 3.0

This nifty looking tree is commonly referred to as the traveler's palm (Ravenala madagascariensis). In reality, it is not a palm at all but rather a close cousin of the bird of paradise plants (Strelitziaceae). It is endemic to Madagascar and the only member of its genus. Even more fascinating is its relationship with another uniquely Madagascan group - the lemurs. But first we must ask, what's in a name?

The name "traveler's palm" has two likely explanations. The first has to do with the orientation of that giant fan of leaves. The tree is said to align its photosynthetic fan in an east-west orientation, which can serve as a crude compass, allowing weary travelers to orient themselves. I found no data to support this. The other possibility comes from the fact that this tree collects a lot of water in its nooks and crannies. Each of its hollow leaf bases can hold upwards of a quart of rain water! Get to it quick, though, because these water stores soon stagnate.

Photo by H. Zell licensed under CC BY-SA 3.0

Flowers are produced between the axils of the leaves and closely resemble those of its bird of paradise cousins. Closer observation will reveal that they are nonetheless unique. For starters, they are large and contained within stout green bracts. Also, they are considerably less showy than the rest of the family. They don't produce any strong odors but they do fill up with copious amounts of sucrose-rich nectar. Finally, the flowers remain closed, even when mature and are amazingly sturdy structures. It may seem odd for a plant to guard its flowers so tightly until you consider how they are pollinated.

It seems fitting that an endemic plant like the traveler's palm would enter into a pollination syndrome with another group of Madagascar endemics. As it turns out, lemurs seem to be the preferred pollinators of this species. Though black lemurs, white fronted lemurs, and greater dwarf lemurs have been recorded visiting these blooms, it appears that the black-and-white ruffed lemur manages a bulk of the pollination services for this plant.

Watching the lemurs feed, one quickly understands why the flowers are so stout. Lemurs force open the blooms to get at the nectar inside. The long muzzles of the black-and-white ruffed lemur seem especially suited for accessing the energy-rich nectar within. The flowers themselves seem primed for such activity as well. The enclosed anthers are held under great tension. When a lemur pries apart the petals, the anthers spring forward and dust its muzzle with pollen. Using both its hands and feet, the lemur must wedge its face down into the nectar chamber in order to take a sip. In doing so, it inevitably comes into contact with the stigma. Thus, pollination is achieved. Once fertilized, the traveler's palm produces seeds that are covered in beautiful blue arils.

Photo by Jeffdelonge licensed under CC BY-SA 3.0

All in all, this is one unique plant. Though its not the only plant to utilize lemurs as pollinators, it is nonetheless one of the more remarkable examples. Its stunning appearance has made it into something of a horticultural celebrity and one can usually find the traveler's palm growing in larger botanical gardens around the world. Though the traveler's palm itself is not endangered, its lemur pollinators certainly are. As I have said time and again, plants do not operate in a vacuum. To save a species, one must consider the entirety of its habitat. This is why land conservation is so vitally important. Support a land conservancy today!

Photo Credits: [1] [2]

Further Reading: [1] [2] [3]