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]

Trees In Spring

Spring is a wonderful time to observe trees. After a long, dreary winter they burst into action. For many species, spring is the time for reproduction.

Species in this episode:

-Serviceberry (Amelanchier sp.)

-Norway maple (Acer platanoides)

-Eastern redcedar (Juniperus virginiana)

-Sugar maple (Acer saccharum)

-Saucer magnolia (Magnolia x soulangeana)

Producer, Writer, Creator, Host: Matt Candeias (http://www.indefenseofplants.com)

Producer, Editor, Camera: Grant Czadzeck (http://www.grantczadzeck.com)

Early Spring Ephemerals

Join us as we go in search of some of the earliest spring ephemerals. In this episode we come face to face with the aptly named harbinger of spring (Erigenia bulbosa) and the lovely Hepatica nobilis.

Producer, Editor, Camera: Grant Czadzeck (http://www.grantczadzeck.com)

Music by
Artist: Stranger In My Town
Track: Air
https://strangerinmytown.bandcamp.com/

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]

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]

Mt. Cuba Center Puts Nativars to the Test

By this point, most gardeners will have undoubtedly heard about the importance of using native plants in our landscapes. Though the idea is not new, Doug Tallamy’s landmark publication “Bringing Nature Home” put native plants on the radar for more gardeners than ever. There is no debate that utilizing native plants in our landscapes offers us a chance to bring back some of the biodiversity that was lost when our homes and work places were built. And, at the end of the day, who doesn’t love the sight of a swallowtail butterfly flitting from flower to flower or a pair of warblers nesting in their Viburnum? The rise of native plants in horticulture and landscaping is truly something worth celebrating.

At the same time, however, capitalism is capitalism, and many nurseries are starting to jump on the bandwagon in alarming ways. The rise of native cultivars or “nativars” is troubling to many. Nativars are unique forms, colors, and shapes of our beloved native plants which have been selected and propagated by nurseries and plant breeders. This has led many to denounce the practice of planting nativars as a slap in the face to the concept of native gardening.

Nativars are frequently seen as unnatural mutant versions of their wild counterparts whose use overlooks the whole point of natives in the first place. Take, for instance, the popularity of double flowered nativars. These plants have been selected for an over-production of sepals and petals that can be so dense that they preclude visitation by pollinators. Another example that will be familiar to most are the bright blue hydrangeas that have become to popular. These shrubs have been selected for producing bright, showy flowers that, depending on your soil chemistry, exhibit a stunning blue coloration. The downside here is that all of those flowers are sterile and produce no nectar or pollen for visiting insects.

It would seem that nativars are a slippery slope to yet another sterile landscape incapable of supporting biodiversity. However, anecdotes don’t equal data and that is where places like Mt. Cuba Center come in. Located in northern Delaware, Mt. Cuba is doing something quite amazing for the sake of environmentally friendly landscaping – they are putting plants to the test.

Mt. Cuba has been running trial garden research and experiments on native plants and their nativars for over a decade. The goal of this research is to generate and analyze data in order to help the public make better, more sustainable choices for their yards. Mt. Cuba aims to better understand and quantify the horticultural and ecological value of native plants and related nativars in order to better understand the various ecosystem services these plants provide. In collaboration with academic institutions in the region, popular nativars are established and grown under similar conditions to those experienced in the yards of your average gardener. They are monitored for years to assess their overall health, performance, and ability to support wildlife. Thanks to the help of countless volunteers, these trial gardens paint a holistic picture of each plant and related nativars that is sorely lacking from the gardening lexicon.

This is very exciting research to say the least. The data coming out of the Mt. Cuba trial gardens may both surprise and excite gardeners throughout the mid-Atlantic region of North America. For instance, their latest report looked at some of the most common Phlox varieties on the market. At the top of this list is Garden Phlox (Phlox paniculata). This lovely species is native throughout much of the eastern United States and has become quite a rockstar in the nursery trade. Over 580 cultivars and hybrids have been named to date and no doubt many more will be introduced in the future. Amazingly, many of these Phlox nativars are being developed in the Netherlands. As such, Phlox arriving in regions of the US with vastly different climates often fall victim to novel diseases they never encountered in Europe. What’s more, people often plant these nativars in hopes of attracting butterflies to their garden. Despite their popularity for attracting various lepidopterans, no one has ever tested whether or not the nativars perform as well as their native progenitor.

Phlox paniculata 'Delta Snow'

Starting in 2015, Mt. Cuba began trials on 66 selections and hybrids of Garden Phlox along with 28 other sun-loving types of Phlox. The plants were observed on a regular basis to see which of the nativars experienced the least amount of disease and attracted the most insects. The clear winner of these trails is a nativar known as Phlox paniculata ‘Jeana’. This particular selection was discovered growing along the Harpeth River in Tennessee and is known for having the smallest flowers of any of the Garden Phlox varieties. It also has the reputation for being rather resistant to powdery mildew. Alongside other selections such as Delta Sno’ and David, Jeana really held up to this reputation.

As far as butterflies are concerned, Jeana blew its competition out of the water. Throughout the observation period, Jeana plants received over 530 visits from butterflies whereas the second place selection, Lavelle, received 117. A graduate student at the University of Delaware is studying why exactly the various nativars of Phlox paniculata differ so much in insect visitation. Though they haven’t zeroed in on a single cause at this point, they suggest that the popularity of Jeana might actually have something to do with its small flower size. Perhaps the density of smaller flowers allows butterflies to access more nectar for less effort.

Phlox paniculata ‘Jeana’

Monarda is another genus of North American native plants that has seen an explosion in nativars and hybrids over the last few decades. The popularity of these mints is no surprise to anyone who has spent time around them. Their inflorescence seems to be doing their best impression of a fireworks display, an attribute that isn’t lost on pollinators. These plants are popular with a wide variety of wildlife from solitary bees to voracious hummingbirds. Even after flowering, their seeds provide food for seed-eating birds and many other animals.

As with Garden Phlox, a majority of the commercial selection and hybridization of Monarda occurs in Europe. As a result, resistance to North American plant diseases is not top priority. Many of us have experienced this first hand as our beloved bee balm patch succumbs to aggressive strains of powdery mildew. Though there are many species of Monarda native to North America, most of the plants we encounter are nativars and hybrids of two species – Monarda didyma and Monarda fistulosa.

Monarda fistulosa 'Claire Grace'

Again, Mt. Cuba’s trial gardens put these plants to the test. A total of 40 different Monarda selections were grown, observed, and ranked based on their overall growth and vigor, pollinator attractiveness, and disease resistance. The clear winner of these trials was a naturally-occurring form of M. fistulosa affectionately named ‘Claire Grace.’ Its floral display lasts a total of 3 weeks without waning and managed to attract over 130 visits by butterflies and moths. Though plenty of other insects such as short-tongued bees visited the flowers during the trial period, they are too small to properly access the nectar inside the flower tubes and are therefore not considered effective pollinators.

Another clear winner in terms of pollinators was possibly one of the most stunning Monarda selections in existence – Monarda didyma ‘Jacob Cline’. This tall, red-flowering nativar was a major hit with hummingbirds. During the observation period, Jacob Cline received over 270 visits from these brightly colored birds. Researchers are still trying to figure out why exactly this particular selection was such a hit but they speculate that the large flower size presents ample feeding opportunities for tenacious hummingbirds.

Monarda didyma 'Jacob Cline'

Claire Grace and Jacob Cline also outperformed most of the other selections in terms of disease resistance. Even in the crowded conditions experienced by plants in the trail garden, both selections faired quite well against the dreaded powdery mildew. Though they aren’t completely resistant to it, these and others did not succumb like some selections tend to do. Interestingly enough, most of the other pure species tested in the trial faired quite well against powdery mildew as well. It would appear that Mother Nature better equips these plants than European breeders.

These reports are but two of the many trials that Mt. Cuba has undertaken and there are many, many more on the way. Thanks to the hard work of staff and volunteers, Mt. Cuba is finally putting numbers behind some of our most commonly held assumptions about gardening with native plants and their cultivars. It is impressive to see a place so dedicated to making our landscapes more sustainable and environmentally friendly.

If you would like to find out more about Mt. Cuba’s trial garden as well as download your own copies of the trial garden reports, please make sure to check out https://mtcubacenter.org/research/trial-garden/

Gnetum Are Neat!

Photo by gbohne licensed under CC BY-SA 2.0

As much as I hate to admit it, when I think of gymnosperms my mind autopilots to conifers and ginkgos. I too easily forget about some of the other extant gymnosperm lineages with which we share space on this planet. Whereas one can easily pick out a conifer or a ginkgo from a lineup, some of the other gymnosperms aren't readily recognized as such. One group in particular challenges my gymnosperm search image to the extreme. I am, of course, talking about a family of gymnosperms known as Gnetaceae.

Gnetaceae is home to a single genus, Gnetum, of which there are about 40 species. They can be found growing in tropical forests throughout South America, Africa, and Southeast Asia. Gnetum essentially come in two forms, small trees and larger, scrambling vines. To most passersby, the various Gnetum species appear to be yet another tropical angiosperm with elliptical evergreen leaves. Indeed, the various species of Gnetum exhibit features that suggest a close link with flowering plants. This has led some to hypothesize that they represent a sort of living "link" between gymnosperms and angiosperms. We will get to that in a bit. First, we must taker a closer look at these odd plants.

Photo by Forest and Kim Starr licensed under CC BY 2.0

We will start with their leaves. They are quite strange by gymnosperm standards. Gnetum produce elliptical leaves with reticulate or web-like venation. Also, their vascular tissues contain vessel elements. Such traits are usually associated with dicotyledonous angiosperms. Characteristics such as these explain why the taxonomic position of Gnetaceae has floundered a bit over the years. What about reproduction? Surely that can help gain a better understanding of where this groups stands taxonomically.

Gnetum reproductive bits require a bit of scrutiny. They are certainly not what we would call flowers. They aren't quite cones either. The technical term for gymnosperm reproductive structures are stobili. In Gnetum, these arise from the axils of the leaves. They are strange looking structures to say the least. Male strobili are long and cylindrical. They, of course, produce pollen. They also contain infertile ovules whose function I will get to in a minute. Female strobili, on the other hand, are larger and consist of ovules enclosed in a thin tissue or integument.

Photo by Kware Ji licensed under CC BY 2.0

Pollination in Gnetum is largely accomplished via insects, though wind plays a significant role for some species as well. In insect pollinated species, the female strobili emit a strong odor and secret tiny beads of liquid called "pollination droplets." Pollination droplets are also secreted from the sterile ovules on the male strobili. It was observed that moths were the main visitors for at least two species of Gnetum.  The reason both sexes produce pollination droplets is to ensure that moths will visit multiple individuals in their search for food.

Following pollen transfer, even more angiosperm-like activity takes place. Some Gentum undergo a type of double fertilization that is unique among moat gymnosperm lineages. Double fertilization is largely considered a defining feature of flowering plants. It is a process by which two sperm cells unite with an egg and become the embryo and the nutritive endosperm that will fuel seedling growth. Along with its cousin Ephedra, Gnetum double fertilization also involves two sperm cells, though the end result is a bit different. Instead of forming an embryo and an endosperm, double fertilization in Gentum (and Ephedra) results in the formation of two viable zygotes and no endosperm.

Photo by Forest and Kim Starr licensed under CC BY 2.0

Fertilized seeds gradually swell into large drupe-like structures. Integument tissues develop with the seed, covering it in a fruit-like substance that turns from green to red as it matures. As far as anyone knows, birds are the main seed dispersal agents for most Gnetum species. 

Taken together, their peculiar anatomy and intriguing pollination have led many to suggest that Gnetum are more closely allied to flowering plants than they are gymnosperms. Certainly it is easy to draw lines from one dot to another in this case but the real test lies in DNA. Are they highly derived gymnosperms or possibly a so-called missing link? 

No. Recent work by the Angiosperm Phylogeny Group found that Gnetaceae are more closely related to the family Pinaceae than they are any of the sister angiosperm lineages. Their work also revealed that, although this lineage arose some 250 million years ago, much of the diversity we see today is the result of rapid speciation events during the Oligocene and Miocene. It would appear that these derived gymnosperms are not the missing link they we once thought to be. In fact, the whole concept of an evolutionary missing link is flawed to begin with. 

Photo by Ahmad Fuad Morad licensed under CC BY-NC-SA 2.0

Still, this should not take away from fully appreciating the bizarre nature of this family. The uniqueness of the genus Gnetum is certainly worth celebrating. They serve as a reminder of just how diverse gymnosperms once were. Today they are a mere shadow of their former glory, overshadowed by the bewildering diversity of angiosperms. If you encounter a Gnetum, take the time to appreciate it as a representative of just how strange gymnosperms can be. 

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

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

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]

Cockroaches & Unexpected Partnerships

Photo by Alpsdake licensed under CC BY-SA 4.0

Say "cockroach" and most people will start to squirm. These indefatigable insects are maligned the world over because of a handful of species that have settled in quite nicely among human habitats. The world of cockroaches is far more diverse than most even care to realize, and where they occur naturally, these insects provide important ecological services. For instance, over the last decade or so, researchers have added pollination and seed dispersal to the list of cockroach activities. 

That's right, pollination and seed dispersal. It may seem odd to think of roaches partaking in such interactions but a study published in 2008 provides some of the first evidence that roaches are doing more with plants than eating their decaying tissues. After describing a new species of Clusia in French Guiana, researchers set out to investigate what, if anything, was pollinating it. The plant was named Clusia sellowiana and its flowers emitted a strange scent. 

Cockroach pollinating C. sellowiana. [SOURCE]

The source of this scent was the chemical acetoin. It seemed to be a rather attractive scent as a small variety of insects were observed visiting the flowers. However, only one insect seemed to be performing the bulk of pollination services for this new species - a small cockroach called Amazonia platystylata. It turns out that the roaches are particularly sensitive to acetoin and although they don't have any specific anatomical features for transferring pollen, their rough exoskeleton nonetheless picks up and deposits ample amounts of the stuff. 

It would appear that C. sellowiana has entered into a rather specific relationship with this species of cockroach. Although this is only the second documentation of roach pollination, it certainly suggests that more attention is needed. This Clusia isn't alone in its interactions with cockroaches either. As I hinted above, roaches can now be added to the list of seed dispersers of a small parasitic plant native to Japan. 

View fullsize

 (A) M. humile fruit showing many minute seeds embedded in the less juicy pulp. (B) Fallen fruits. (C) Blattella nipponica feeding on the fruit. (D) Cockroach poop with seeds. (E) Stained cockroach-ingested seeds. [SOURCE]

Monotropastrum humile looks a lot like Monotropa found growing in North America. Indeed, these plants are close cousins, united under the family Ericaceae. Interestingly enough, it was only recently found that camel crickets are playing an important role in the seed dispersal of this species. However, it looks like they aren't the only game in town. Researchers have also found that a forest dwelling cockroach called Blattella nipponica serves as a seed disperser as well. 

The roaches were observed feeding on the fruits of this parasitic plant, consuming pulp and seed alike. What's more, careful observation of their poop revealed that seeds of M. humile passed through the digestive tract unharmed. Cockroaches can travel great distances and therefore may provide an important service in distributing the seeds of a rather obscure parasitic plant. To think that this is an isolated case seems a bit naive. It seems to me like we should pay a little more attention to what cockroaches are doing in forests around the world. 

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

Further Reading: [1] [2]

Bird Pollination Of The Bird Of Paradise

Public domain

Who hasn't stared in wonderment at the inflorescence of a bird of paradise? One doesn't need too much of an imagination to understand how these plants got this common name. Flowers, however, did not evolve in response to our aesthetic tastes. They are solely for sex and in the case of bird of paradise, Strelitzia reginae, pollination involves birds.

In its native range in South Africa, S. reginae is pollinated by sunbirds, primarily the Cape weaver (Ploceus capensis). That alluring floral morphology is wonderfully adapted to maximize the chances of successful cross-pollination by their avian visitors. Cape weavers are looking for a sip of energy rich nectar. To get at said nectar, the birds must perch on the inflorescence. Not any position will do either.

Photo by Forest & Kim Starr licensed under CC BY 3.0

To get their reward, the birds must perch so that their beaks are at just the right angle to reach down into the floral tubes. The plant ensures this by providing a convenient perch. Those fused blue petals are structurally reinforced and actually serve as a convenient perch! Upon alighting on the perch, the hidden anthers are thrust outward from their resting chamber, brushing up against the bird's feet in the process. The Cape weaver doesn't move around much once on the flower so self pollination is minimized.

When the bird visits another plant, the process is repeated and pollination is achieved. Seed set is severely pollen limited. This is a good thing considering how popular they are in cultivation. Plants growing outside of South Africa rarely set seed without a helping hand. However, here in North America, some birds seemed to have figured out how to get at bird of paradise nectar.

[SOURCE]

Observations made in southern California found that at least one species of warbler, the common yellowthroat (Geothlypis trichas), not only made regular visits to a stand of S. reginae, it also seemed to figure out the proper way to do so. Individuals were seen perching on the floral perch and drinking the nectar. They were pretty effective visitors at that. Of the 14,400 inflorescence found within the study area, 88% of them produced viable seed! It seems that far from its native range, S. reginae has a friend in at least one New World warbler. Armed with this knowledge, land owners should be vigilant to ensure this plant doesn't become a problem in climates suitable for its growth.

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

Further Reading: [1]

Ants As Pollinators?

Photo by Ken-ichi Ueda licensed under CC BY-NC 2.0

Ants interact with plants in a variety of beneficial ways. They offer protection, they provide nutrients, they even disperse seeds! When it comes to pollination, however, plants have largely gone elsewhere. That's not to say ants don't get directly involved in the sex lives of plants. At least one plant species native to Spain has been found to be pollinated by ants. Certainly there are probably more examples of ant pollination throughout the plant kingdom, we simply have to look. For example, one possible ant-pollinated plant can be found growing on the west coast of North America.

The dwarf owl's-clover (Triphysaria pusilla) is a small annual member of the broomrape family. It really is a dwarf species, rarely exceeding a few inches in height. What it lacks in size, it makes up for in abundance. Large colonies of these species can be found growing among other low statured herbs in wetter areas like spring-fed grasslands. Their tendency to produce lots of anthocyanin pigments in their tissues means that these maroon colonies really stand out. Like other members of the family, it is a facultative hemiparasite, tapping into the roots of surrounding vegetation with its roots, stealing nutrients and water as the situation demands.

Photo by brewbooks licensed under CC BY-SA 2.0

Flowering in the dwarf owl's-clover is rather inconspicuous. The dense flowering spikes produce minute, tubular, maroon-yellow flowers. It has been observed that, at any given point during the flowering season, only three flowers will have matured on any given plant. Two of these flowers mature their anthers first whereas the remaining flower matures its stigma. This is likely an adaptation for increasing the chances of cross pollination. 

Photo by Richard Droker licensed under CC BY-NC-ND 2.0

Because these flowers hardly qualify as an attractive display for more commonly encountered insect pollinators, it has been hypothesized that ants are the preferred pollinator of this species. Early work even suggested that the dense leaf arrangement facilitates ant movement to and from flowers in any given colony. Although no one has yet quantified the efficacy of ants as pollinators of this species, numerous observations of ants visiting flowers and picking up pollen have been made. Famously, such a scene was filmed for the 1981 documentary "Sexual Encounters of the Floral Kind."

Whether these visits constitute effective pollination remains to be seen. It could be that the ants are nothing more than nectar and pollen thieves. What's more, many ants produce substances from specialized glands that, among other things, destroy pollen. Until someone takes the time to study this interaction, we simply do not know. Sounds like a fun research project to me! 

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

Further Reading: [1]

How Plants Influence Honeybee Caste System

Is has long been known that food fed to larval honeybees influences their development and therefore their place in the hive. Larvae fed a mixture of pollen and honey, often referred to as "bee bread," develop into sterile workers whereas larvae fed special secretions termed "royal jelly" from nurses within the colony will develop into queens. Despite this knowledge, the mechanisms underpinning such drastic developmental differences have remained a mystery... until now.

A team of researchers from Nanjing University in China have uncovered the secret to honeybee caste systems and it all comes down to the plants themselves. It all has to do with tiny molecules within plants called microRNA. In eukaryotic organsisms, microRNA plays a fundamental role in the regulation of gene expression. In plants, they have considerable effects on flower size and color. In doing so, they can make floral displays more attractive to busy honeybees.

As bees collect pollen and nectar, they pick up large quantities of these microRNA molecules. Back in the hive, these products are not distributed equally, which influences the amount of microRNA molecules that are fed to developing larvae. The team found that microRNA molecules are much more concentrated in bee bread than they are in royal jelly. Its this difference in concentrations that appears to be at the root of the caste system.

Larvae that were fed bee bread full of microRNA molecules developed smaller bodies and reduced, sterile ovaries. In other words, they developed into the worker class. Alternatively, larvae fed royal jelly, which has much lower concentrations of microRNA, developed along a more "normal" pathway, complete with functioning ovaries and a fuller body size; they developed into queens.

All of this hints at a deep co-evolutionary relationship. The fact that these microRNA molecules not only make plants more attractive to pollinators but also influence the caste system of these insects is quite remarkable. Additionally, this opens up new doors into understanding co-evolutionary dynamics. If horizontal transfer of regulatory molecules between two vastly different kingdoms of life can manifest in such important ecological relationships, there is no telling what more is awaiting discovery. 

Further Reading: [1]

Birds Work a Double Shift For Osmoxylon

Photo by Forest & Kim Starr licensed under CC BY 3.0

Plants go to great lengths to achieve pollination. Some can be tricky, luring in pollinators with a promise of food where there is none. Others, however, really sweeten the deal with ample food reserves. At least one genus of plants has taken this to the extreme, using the same techniques for pollination as it does for seed dispersal. I present to you the genus Osmoxylon.

Comprised of roughly 60 species spread around parts of southeast Asia and the western Pacific, the genus Osmoxylon hail from a variety of habitats. Some live in the deep shade of the forest understory whereas others prefer more open conditions. They range in size from medium sized shrubs to small trees and, upon flowering, their place within the family Araliaceae becomes more apparent.

Photo by Mokkie licensed under CC BY-SA 3.0

Look closely at the flowers, however, and you might notice a strange pattern. It would appear that as soon as flowers develop, the plant has already produced berries. How could this be? Are there cleistogamous flowers we aren't aware of? Not quite. The truth, in fact, is quite peculiar. Of the various characteristics of the genus, one that repeatedly stands out is the production of pseudo-fruits. As the fertile flowers begin to produce pollen, these fake fruits begin to ripen. There aren't any seed inside. In truth, I don't think they can technically be called fruits at all. So, why are they there?

Although actual observations will be required to say for sure, the running hypothesis is that these pseudo-fruits have evolved in response to the presence of birds. They are pretty fleshy and would make a decent meal. It is thought that as birds land on the umbel to eat these pseudo-fruits, they invariably pick up pollen in the process. The bird the exchanges pollen with every subsequent plant it visits. Thus, pollination is achieved.

The relationship with birds doesn't end here. Like other members of this family, pollination results in the formation of actual fruits full of seeds. Birds are known for their seed dispersal abilities and the Osmoxylon capitalize on that as well. As such, the reproductive input of their avian neighbors is thought to be two-fold. Not only are birds potentially great pollinators, they are also great seed dispersers, taking fruits far and wide and depositing them in nutrient-rich packets wherever they poop.

Photo Credits: [1] [2]

Further Reading: [1]

Closed on Account of Weather

Photo by Alpsdake licensed under CC BY-SA 3.0

Alpine and tundra zones are harsh habitats for any organism. Favorable conditions are fleeting and nasty weather can crop up in the blink of an eye. Whereas animals in these habitats can take cover, plants don't have that luxury. They are stuck in place and have to deal with whatever comes their way. Despite these challenges, myriad plant species have adapted to these conditions and thrive where other plants would perish. The intense selection pressures of these habitats have led to some fascinating evolutionary adaptations, especially when it comes to reproduction.

Take, for instance, the Arctic gentian (Gentianodes algida). This lovely plant can be found growing in alpine and tundra habitats in both North America and Asia. Like most plants of these habitats, the Arctic gentian has a low growth habit, forming a dense cluster of fleshy, narrow leaves that hug the ground. This protects the plant from blustering winds and extreme cold. From late July until early September, when the short growing season is nearly over, this wonderful plant comes into bloom. 

Clusters of white and blue speckled flowers are borne on short stems and, unlike other angiosperms that readily self-pollinate under harsh conditions, the Arctic gentian requires outcrossing to set seed. This can be troublesome. As you can imagine, pollinators can be in short supply in these habitats. What's more, with conditions changing on a dime, the flowers must be able to cope with whatever comes their way. The Arctic gentian is not helpless though. It has an interesting adaptation to these habitats and it involves movement.

Only a handful of plant species are known for their ability to move their various organs with relative rapidity. This gentian probably doesn't make that list very often. However, it probably should as its flowers are capable of responding to changes in weather by closing up shop. It is not alone in this behavior. Plenty of plant species will close their flowers on cold, dreary days. What is so special about the Arctic gentian is that it seems especially attuned to the weather. Within minutes of an incoming thunderstorm (a daily occurrence in the Rockies, for example) the Arctic gentian will close up its flowers. This is done via changes in turgor pressure within the cells. But what is the signal that cues this gentian in that a storm is fast approaching?

Researchers have investigated multiple stimuli in search of the answer. Plants don't seem to respond to changes in sunlight, wind, or humidity. Instead, temperature seemed to be the only signal capable of eliciting this response. When temperatures suddenly drop, the flowers will begin to close. Only when the temperature begins to rise will the flowers reopen. These movements are quite rapid too. Flowers will close completely within 6 - 10 minutes of a rapid decease in temperature. The reverse takes a bit longer, with most flowers needing 25 - 40 minutes to reopen.

So, why does the plant go through the trouble of closing up shop? It all has to do with sexual reproduction in these harsh conditions. Because this species doesn't self, pollen is at a premium. The plant simply can't afford the risk of rain washing it all away. The tightly closed flowers prevent that from happening. Also, wet flowers have been shown to discourage pollinators, even when favorable weather returns. Aside from interfering with pollen, rain also dilutes nectar, reducing its energy content and thus reducing the reward for any bee that would potentially visit the flower.

Being able to rapidly respond in changes in weather is important in these volatile habitats. Plants must be able to cope otherwise they risk extirpation. By closing up its flowers during inclement weather, the Arctic gentian is able to protect its vital reproductive resources.

Photo Credits: [1]

Further Reading: [1]

Flowers That Mimic Flies

Photo by Claire Woods licensed under CC BY-NC-ND 2.0

Pollination is one of the major advantages flowering plants have over the rest of the botanical tree. With a few exceptions, flowers have cornered this market. It no doubt has played a significant role in their rise to dominance on the landscape. The importance of flowers is highlighted by the fact that they are costly structures. Because they don't photosynthesize, all plants take a hit on energy reserves when it comes time to flower. Sepals, petals, pollen, nectar, all of these take a lot of energy to produce which is why some plants cheat the system a bit. 

Sexual mimicry is one form of ruse that has evolved repeatedly. The flowers of such tricksters mimic receptive female insects waiting for a mate. The evolution of such a strategy taps into something far deeper in the mind of animals than food. It taps into the need to reproduce and that is one need animals don't readily forego. As such, sexually deceptive flowers usually do away with the production of costly substances such as nectar. They simply don't need it to attract their pollinators. 

Photo by Dr. Alexey Yakovlev licensed under CC BY-SA 2.0

By and large, the world of sexual mimicry in plants is one played out mainly by orchids. However, there exists an interesting exception to this rule. A daisy that goes by the scientific name Gorteria diffusa has evolved a sexually deceptive floral strategy of its own. Native to South Africa, this daisy is at home in its Mediterranean climate. It produces stunning orange flowers that very much look like those of a daisy. On certain petals of the ray florets, one will notice peculiar black spots. From region to region there seems to be a lot of variation in the expression of these spots but all are textured thanks to a complex of different cell types. 

The spots may seem like random patterns until the flowers are visited by their pollinator - a tiny bee-fly known scientifically as Megapalpus nitidus. With flies present, one can sort of see a resemblance. This would not be a mistake on the observers part. Indeed, when researchers removed or altered these spots, bee-fly visitation significantly decreased. Although this didn't seem to influence seed production, it nonetheless suggests that those spots are there for the flies. 

When researchers painted spots on to non-textured petals, the bee-flies ignored those as well. It appears that the texture of the spots makes a big difference to visiting flies. What's more, although female flies visited the flowers, a majority of the visits were by males. It appears that the presence of these spots is keying in on the mate-seeking and aggregation behavior of their bee-fly pollinators. Further investigation has revealed that the spots even reflect the same kind of UV light as the flies themselves, making the ruse all the more accurate. This case of sexual mimicry is unique among this family. No other member of the family Asteraceae exhibits such reproductive traits (that we know of). Although it doesn't seem like seed production is pollinator limited, it certainly increases the chance of cross pollination with unrelated individuals.

Photo Credits: [1] [2]

Further Reading: [1] [2]