A Peculiar Case of Bird Pollination

Via Johnson and Brown [SOURCE]

When we think of bird pollination, we often conjure images of a hummingbird sipping nectar from a long, tubular, red flower. Certainly the selection pressures brought about from entering into a pollination syndrome with birds has led to convergence in floral morphology across a wide array of different plant genera. Still, just when we think we have the natural world figured out, something new is discovered that adds more complexity into the mix. Nowhere is this more apparent than the peculiar relationship between an orchid and a bird native to South Africa.

The orchid in question is known scientifically as Disa chrysostachya. It is a bit of a black sheep of the genus. Whereas most Disa orchids produce a few large, showy flowers, this species produces a spike that is densely packed with minute flowers. They range from orange to red and, like most other bird pollinated flowers, produce no scent. 

Take the time to observe them in the field and you may notice that the malachite sunbird is a frequent visitor. The sunbirds perch themselves firmly on the spike and probe the shallow nectar spurs on each flower. At this point you may be thinking that the pollen sacs, or pollinia, of the orchid are affixed to the beak of the bird but, alas, you would be wrong. 

Closer inspection of the flowers reveal that the morphology and positioning of the pollinia are such that they simply cannot attach to the beak of the bird. The same goes for any potential insect visitors. The plant seems to have assured that only something quite specific can pick up the pollen. To see what is really going on, you would have to take a look at the sunbird's feet. 

That's right, feet. When a sunbird feeds at the flowers of D. chrysostachya, its feet position themselves onto the stiffened lower portion of the flower. This is the perfect spot to come into contact with the sticky pollinia. As the bird feeds, they pick up the pollinia on their claws! The next time the bird lands to feed, it will inevitably deposit that pollen. The orchids seemed to have benefited from the fact that once perched, sunbirds don't often reposition themselves on the flower spike. In this way, self pollination is minimized. A close relative, D. satyriopsis, has also appeared to enter into a pollination with sunbirds in a similar way. 

Though it may seem inefficient, research has shown that this pollination mechanism is quite successful for the orchid.The pollinia themselves stick quite strongly so that no amount of scuffing on branches or preening with beaks can dislodge them. Once pollination has been achieved, each flower is capable of producing thousands upon thousands of seeds.

Photo Credit: Johnson and Brown

Further Reading: [1]

Color Changing Asters

Fall is here and the asters are out in force. Their floral displays are some of the last we will see before the first fall frost takes its toll. Their beauty is something of legend and I could sit in a field and stare at them for hours. In doing so, an interesting pattern becomes apparent. Have you ever noticed that the disc flowers of the many aster species gradually turn from yellow to red? Whereas this certainly correlates with age, there must be some sort of evolutionary reason for this.

Indeed, there is. If you sat and watched as bees hurriedly dashed from plant to plant, you may notice that they seem to prefer flowers with yellow discs over those with red. The plot thickens. What about these different colored discs makes them more or less appealing to bees desperately in need of fuel? The answer is pollen.

A closer observation would reveal that yellow disks contain more pollen than those with red discs. Of course, this does relate to age. Flowers with red discs are older and have already had most of their pollen removed. In this way, the color change seems to be signaling that the older flowers are not worth visiting. Certainly the bees notice this. But why go through the trouble of keeping spent flowers? Why not speed up senescence and pour that extra energy into seed production?

Well, its all about cues. Bees being the epitome of search image foragers are more likely to visit plants with larger floral displays. By retaining these old, spent flowers, the asters are maintaining a larger sign post that ensures continued pollinator visitation and thus increases their chances of cross pollination. The bees simply learn over time to ignore the red disc flowers once they have landed. In this way, they maximize their benefit as well.

Further Reading: [1]

Three Cheers for Fungus Gnats!

Photo by Canyon Country Discovery Center licensed under CC BY-ND 2.0

Bees, butterflies, bats, and birds... Most of us are all too familiar (and thankful) for their roles as plant pollinators. However, there are some unsung heroes of this niche and one of them are the often overlooked fungus gnats.

Pollinators, for good reason, are one of the largest selective pressures on flower evolution. As flowers evolve to cater to a specific kind of pollinator, be it a bird, a bee, or even fungus gnats, we refer to it as a pollinator syndrome. I have been enchanted by the flowers of the genus Mitella ever since I stumbled across them. As you can see in the picture, they are generally saucer shaped and have snowflake-like appendages protruding from their rim. I wondered, what kind of pollinator syndrome would produce such delicate beauty?

A quick search in the literature turned up a paper from a team of botanists based out of the University of Idaho. The paper outlines work done across a wide range of genera in the Saxifragaceae family. They looked at flower morphology and, through hours of field observation, found a common theme in many species. Those with small, white, saucer-shaped flowers, such as those of Mitella pentandra, all seem to be pollinated by fungus gnats. Fungus gnats are themselves quite small and their larvae live in moist soils, feeding on fungi. As it turns out, the adults are avid pollinators of many plant species and because of this, some species, like M. pentandra, have evolved a pollinator syndrome with them.

The research team also found a strong correlation between fungus gnat flowers and habitat type. They all seemed to be tied to moist forest habitats. This is because moist forests are the only place fungus gnats can live. Plants in drier habitats rarely come into contact with fungus gnats and therefore have no selective pressures to cater to these insects.

I love it when general observations based on aesthetics lead to a deeper understanding of what is going on outside.

Photo Credit: Four Corners School of Outdoor Education (http://bit.ly/1jmNLDR)

Further Reading:
http://bit.ly/1VFiHY4

What is the Most Common Flower Color?

Photo by Mor licensed under CC BY-NC 2.0

Have you ever wondered what the most common flower color is? If one were to tally up all the known flowering plants, what color or colors would come out on top? I have pondered this time and again and I for some reason have a bias towards yellow. I think it is a symptom of where I live. In fact, I think flower color in general can, in part, be considered a function of geographic location. Each region of the world has its own specific pollinators driving selection for flower color. I decided to finally try and track down an answer to this question. 

The truth of the matter is, no one really knows. There is simply no database out there that fully characterizes all the colors flowers can be, let alone rank them by abundance. When you really think about it in the context of real world examples, it makes sense that this would be a daunting task. The first question becomes "how do we define the color of a flower?" This may seem silly but think about it. How many times has a field guide said one thing and reality says another? This is the main reason I don't use Peterson's Field Guide to Wildflowers. Colors vary from genus to genus and heck, they even vary within a species. A plant growing in one area may look one way while the same species growing in another area can look totally different. Far from being simply a function of genes, flower color can be just as dependent on growing conditions. 

Also, what one botanist calls red may not be what everyone else calls red. Barring a persons ability to see all of the visible light spectrum, there is no set standard, for flowers at least, as to where we draw the lines between colors. What we end up with at the end of the day are lumped packages of color pertaining to a chunk of the spectrum visible to us. It is actually an easier question to ask "what is the rarest flower color?" To that, most botanists will probably say black. To the best of my knowledge, there is only one species of plant in the world with truly black flowers. The rest are more accurately deep shades of red or purple. True blue is another rare color among flowers for the same reason. 

After a few hours (more than I should have dedicated to the cause) I came up with one satisfying answer and to sum it all up, I will put it this way: We simply have no idea what the most common flower color is in the world but it's probably green. We tend to only pay attention to the showiest flowers. Big or small, we like bright colors and we like weird colors. All the rest just get glazed over. In reality, many plant species, especially trees, produce small, non-descript green flowers. For this reason I would say that green is a safe default until someone or a group of someones puts in the time that would be needed to put any meaningful numbers to this inquiry.

Photo Credit: Mor (http://bit.ly/1y0WnJd)

Throwing it to the Wind

Though many of you may be cursing this fact, in the temperate regions of the north, wind pollinated trees are bursting into bloom. Their flowers aren't very showy. They don't have to be. Instead of relying on other organisms for pollination, these trees throw it to the wind, literally.

It is an interesting observation to note that the instances of wind pollinated tree species increases with latitude and elevation. This makes a lot of sense. It is most effective in open areas where wind is at its strongest. That is why many wind-pollinated trees get down to business before they leaf out.

The fewer obstructions the better. Also, pollinators can be hard to come by both at high elevation and high latitudes. Therefore, why not let the wind do all the work? This is also why wind-pollination is most common in early succession and large canopy species. Similarly, this is also why you rarely encounter wind-pollinated trees in the tropics. Leaves are out year round and pollinators are in abundance.

Without pollinators, wind-pollinated trees don't need to invest in showy flowers. That is why they often go unnoticed by folks. Instead, they pour their energy into pollen production. Your irritated sinuses are a vivid reminder of that fact. Wind pollination is risky. It relies mostly on chance. Therefore, the more pollen a tree pumps out, the more likely it will bump into a female. However, some trees like red maples (Acer rubrum) combine tactics, relying on both wind and hardy spring pollinators for their reproduction.

Whether you love this time of year or dread it, it is nonetheless interesting to see how static organisms like trees cope with the difficulties of sexual reproduction. I enjoy sitting in my yard and watching pines billow pollen like smoke from a fire. If anything, it is a stark reminder of how important sexual reproduction is to the myriad organisms on this planet.

Further Reading:
http://bit.ly/1qnRUm2

Groundnut

As common names go, groundnut doesn't quite seem fitting for such a distinctive plant. Known scientifically as Apios americana, this leguminous vine can be found growing along a variety of edge habitats throughout much of eastern North America. It becomes most obvious to passers by from July through September when it is flowering. 

Okay, to be fair, groundnut is a fairly accurate description. Not only are the seeds of this vine edible, so too are the starchy tubers it grows from. However, I think this all detracts from a rather intriguing ecology. Populations of groundnut occur in one of two forms - diploid (2 sets of chromosomes) or triploid (three sets of chromosomes). It would seem that entire populations can sometimes consist of the triploid variety. 

This is a bit odd because triploid plants are sterile. Though they produce seemingly functional flowers, they never produce seed. Instead, these populations reproduce vegetatively via their underground tubers. Other than their lack of reproductive ability, there doesn't seem to be any other noticeable differences between diploids and triploids. Whatever the reason, it is obviously working for the groundnut.

Via Internet Archive Book Images under Public Domain

Speaking of reproduction, there seems to be a bit of mystery concerning the types of pollinators targeted by this vine. Groundnut flowers, with their carrion-like appearance and strange odor, may be attracting carrion flies. Some authors are rather set on this hypothesis despite very little evidence. A more thorough investigation into the pollination ecology of groundnut revealed that bees were the only visitors, however, nothing conclusive could be said about their effectiveness.

What can be said is that the flowers require insects of a certain size for pollination to occur. The flowers themselves are essentially miniature spring traps. When insects of a certain size land on the flowers they trigger the release of the anthers, which slam into the insect, dusting it with pollen. This is a very similar strategy to a close relative of groundnut, alfalfa (Medicago sativa), which is definitely bee pollinated. 

Despite all of the confusion surrounding groundnut, it is nonetheless a great species. It fixes nitrogen, provides food for wildlife and humans alike, and looks really cool to boot. This would be a great addition to a native plant garden throughout its range. 

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

Pollination Plasticity

© Danny Keßler

Pollinators are great -- that is, unless they also feed upon the plant they are pollinating. In the arid regions of western North America, Nicotiana attenuata, sometimes referred to as coyote tobacco, has this very problem. 

Blooming at night, its white flowers are heavily scented, which attracts its pollinator, a species of hawkmoth known to science as Manduca quinquemaculata. Female hawkmoths do a little bit more than just grab a sip of nectar. Their larvae feed on members of the tobacco family and, as anyone with tomatoes can tell you, they have a voracious apatite. Visiting female moths use the meal break as a chance to lay their eggs. However, this does not have to be a death sentence for the plant. Researchers noticed a strange thing about N. attenuata plants that had feeding damage from hawkmoth caterpillars. Their flowers seemed to change.

Photo by Stan Shebs licensed under CC BY-SA 3.0

And change they did. Coyote tobacco plants with caterpillars will start to produce flowers that open during the day, instead of at night. The plants also stopped producing a scent. What's more, the flowers didn't open very far either. What is the reason for these drastic changes? Are the plants stressed out from the caterpillar attack?

Not exactly. In fact, the answer is quite remarkable. As it it turns out, plants with caterpillars munching on them were intentionally shifting their entire reproductive strategy to avoid the larvae of their intended pollinators. Flowers that open during the day no longer attracted the attention of moths, which reduced the number of new eggs being laid. Instead, the flowers started attracting the attention of hummingbirds. Hummingbirds are pretty effective as pollinators and their offspring don't eat the plants that their parents feed on. 

Manduca quinquemaculata adult male. Photo by Didier Descouens licensed under CC BY-SA 4.0

So, how does the plant know when its being fed upon? Caterpillar spit. Chemicals in the saliva of the caterpillar trigger a chemical response within the plant that tells it to start ramping up defenses (of which nicotine is one). This signaling cascade also tells the plant to start producing day opening flowers instead of night opening flowers. It just goes to show you how a little attention to detail can uncover some amazing aspects of the world around us. 

Photo Credit: Danny Kessler, MPI chemische Ökologie, Wikimedia Commons

Further Reading: [1] [2]

Flower Color Beyond What We Can See

Photo by Plantsurfer licensed under CC BY-SA 3.0

Despite their aesthetic appeal, flowers are not here to dazzle us. While they have enticed us to spread the offspring of many species around the globe, flowers have one purpose and one purpose only - sex. 

There are many different and even tricky ways flowers manage pollination. The most common and by far the most widely utilized is the use of insects. Though flowers look like they have done everything they can to attract pollinators, we can only see a narrow range of the electromagnetic spectrum. What we see as visible light is only a mere fraction of what is really out there. 

Many insects see well into the ultraviolet range and this has caused some very interesting evolutionary adaptations in flowers to attract insects to their business parts. When viewed with UV cameras, many species of plants have seemed to have drawn maps and arrows to their anthers and stigmas. It is amazing to witness a species of say Potentilla with, to us, solid yellow petals in this manner. The patterns that appear are striking! There are far too many examples to go into detail on this subject so instead, here is a great website to show you some examples 

http://www.naturfotograf.com/UV_flowers_list.html

Invasive Ants Destroy Plant Sex Lives

Photo by Lalithamba licensed under CC BY 2.0

For all of the amazing symbioses ants and plants share, there is one thing ants seem to get in the way of... plant sex. That's right, plants have found a use for ants in pretty much every way except for when it comes to reproduction (with some exceptions of course). Ants being what they are, they can easily become a force to be reckoned with. For this reason, many plant species have co-opted ants as defense agents, luring them in with nectar-releasing glands, a resource that ants guard quite heavily. 

When it comes to flowering, however, ants can become a bit overbearing. Research done at the University of Toronto shows that the invasive European fire ant has a tendency to guard floral nectar so heavily that they chase away pollinators. By observing fire ants and bumblebees, they found that ants change bumblebee foraging behaviors. The fire ants often harassed and attacked bumblebees as they visited flowers, causing them to spend significantly less time at each flower, a fact that could very well result in reduced pollination for the plant in question. 

This reduction in pollination is made even more apparent for dioecious plants. Since ants are after nectar and not pollen, male flowers received more bumblebee visits than nectar-producing female flowers. This could become quite damaging in regions with heavy fire ant infestations. 

As it turns out, the ants don't even need to be present to ward off bumblebees. The mere scent of ants was enough to cause bumblebees to avoid flowers. They apparently associated the ant smell with being harassed and are more likely to not chance a visit. Of course, this study was performed on using an invasive ant species. Because so many plant species recruit ants for things like protection and seed dispersal, it is likely that under natural conditions, the benefit of associating with ants far outweighs any costs to reproductive fitness. More work is needed to see if other ant specie exhibit such aggressive behavior towards pollinators. 

Photo Credit: Lalithamba (https://www.flickr.com/people/45835639@N04)

Further Reading:

 http://www.researchgate.net/profile/James_Thomson13/publication/259319739_Ants_and_Ant_Scent_Reduce_Bumblebee_Pollination_of_Artificial_Flowers/links/554b8fd90cf21ed213595eff.pdf

Cannonball!

Photo by Joel Abroad licensed under CC BY-NC-SA 2.0

There are some trees out there that you probably shouldn't hug. Couroupita guianensis is one such example. You certainly wouldn't want to risk standing at the base of one for any length of time. What looks like a vine covering the trunk of each tree is actually the reproductive structures of this species. Beautiful flowers give way to hefty seed pods, earning this tree its common name, the cannonball tree. 

A native to Central and South America as well as parts of the Caribbean, the distinctive flowers of this tree are born on long stalks that emerge right out of the trunk. This is known as "cauliflory." Trees like this can cause you to do a double take. Indeed, it is strange seeing flowers on a trunk instead of at the tips of branches. It is likely that this type of flowering has evolved as a form of resource partitioning. Instead of vying for pollinators or seed dispersers way up in the canopy, trees like C. guianensis may opt for them at lower levels in the forest where competition may be lower. 

In the case of C. guianensis, the main pollinators are carpenter bees. The peculiar flowers don't produce any nectar, however, they make up for this by offering copious amounts of pollen. The strangest aspect of this is that two different type of pollen are produced. Each flower has two sets of anthers, one set forms a ring around the center of the flower and the other set is located at the tip of the petal that is bent inward forming a hood. What's more, the pollen grains produced by each set differs in appearance with the ring pollen being white and smaller and the hood pollen being yellow and larger. As it turns out, the hood pollen is mostly sterile whereas the ring pollen is fertile. When a bee lands on the hood of the flower looking for pollen, it is attracted to the larger grains. As it harvests pollen from the hood its body is pushed up against the ring pollen, which is carried to the next flower, where the process is repeated and the flower fertilized.

Photo by Mauricio Mercadante licensed under CC BY-NC-SA 2.0

After fertilization, large capsules are produced that sort of resemble coconuts or canon balls. Being a member of the Brazil nut family, these capsules can measure upwards of 8 inches in diameter and are chock full of pulp and seeds. Each capsule eventually falls from the tree, cracking open as it smashes into the ground. The capsules can be so large and heavy that anyone unfortunate enough to be standing under one when it fell is likely to be killed by the impact. The pulp inside is said to smell quite awful, which is a attractive to various seed dispersers around the forest.  Peccaries as well as large rodents like the paca eat the seeds, which germinate quite well after passing through their gut. 

Couroupita guianensis has been planted far outside of its natural range for a variety of reasons. It is likely that anyone visiting a botanical garden in the tropics will come across one of these odd trees. Any gardener worth their weight would do well to keep this tree away from footpaths. This is a species best admired from a distance. Aside from avoiding a head crushing blow from one of those seed capsules, this is a tree that must be seen in its entirety to truly appreciate. 

Photo Credits: [1] [2]

Further Reading: [1] [2]

Noble Rhubarb

[SOURCE]

The Himalayas. If there was ever a natural wonder worthy of the title "epic" it would certainly be these towering peaks. Home to some of the tallest points on our planet, these ragged peaks are best known for the near insurmountable challenges faced by adventurers from all around the world. Considering their elevation, it would seem that permanent life simply isn't possible on these mountains. However, this could not be further from the truth. Among sprawling shrubs and diminutive herbs towers one of the most peculiar plants known to the world. To make things more interesting, it is a relative of rhubarb, a denizen of gardens and pies throughout much more hospitable climates. 

Meet the noble rhubarb, Rheum nobile. Growing at elevations between 13,000 and 15,000 feet (4000–4800 m), this species is quite deserving of its noble status. Plants growing at such elevations face some serious challenges. Temperatures regularly drop well below freezing and there is no shortage of damaging UV radiation. As with most alpine zones, a majority of plants cope with these conditions by growing prostrate over the ground and taking what little refuge they can find behind rocks. Not Rheum nobile. This member of the buckwheat family can grow to heights of 6 feet, making it easily the tallest plant around for miles. 

The most striking feature of this plant is the large spire of translucent bracts. These modified leaves contain no chlorophyll and thus do not serve as centers for photosynthesis. Instead, these structures are there to protect and warm the plant. Tucked behind the bracts are the flowers. If they were to be exposed to the elements, they would either freeze or be fried by UV radiation. Instead, these ghostly bracts contain specialized pigments that filter out damaging UV wavelengths while at the same time creating a favorable microclimate for the flowers and seeds to develop. In essence, the plant grows its own greenhouse.

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

As a result, temperatures within the plant can be as much as 10 degrees warmer than the ambient temperatures outside. At such elevations, this is a real boost to its reproductive efforts. Even more of a challenge is the fact that at this elevation, pollinators are often in short supply. Plants have to do what they can to get their attention. Not only does Rheum nobile offer a visual cue that is in stark contrast to its bleak surroundings, it also goes about attracting pollinators chemically as well.

Rheum nobile has struck up a mutualistic relationship with fungus gnats living at these altitudes. The plant produces a single chemical compound that attracts the female fungus gnats. The females lay their eggs in the developing seeds of the plant but, in return, pollinate far more flowers than they can parasitize. These organisms have managed to strike a balance in these mountains. In return for pollination, the fungus gnats have a warm place to raise their young that is sheltered from the damaging UV radiation outside. 

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

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

Cast In Iron

Photo by Phillip Merritt licensed under CC BY-NC-SA 2.0

When it comes to hardy houseplants, few species can hold a candle to the Aspidistra. With their ability to tolerate dismal lighting conditions and less than stellar air quality, it is no wonder the this genus was a favorite among the middle class during the Victorian era. They were so common during that time period that George Orwell himself used them as a metaphor in his 1936 novel "Keep the Aspidistra Flying." Today they are nothing more than space fillers. Commonly known as "cast iron plants," they are a natural step up from silken foliage in waiting rooms and cubicles. They can virtually be ignored and still maintain their composure. For a houseplant, this is pretty incredible. However, this genus did not originate in the home. It is just as wild as any other plant out there. What are the Aspidistra and where do they come from?

Photo by justinleif licensed under CC BY-NC-SA 2.0

With their long, strap-like leaves that seem to pop out of the dirt at random, it is not readily apparent that these plants belong to the same family as asparagus - Asparagaceae. Since the 1980's, botanists have described upwards of 93 different species within the genus. They are native to eastern Asia and hit their peak diversity in China and Vietnam. Many species within this genus are endemic to these areas. 

Photo by Scott Zona licensed under CC BY-NC 2.0

Aspidistra as a whole are understory species, growing on the ground underneath dense canopies of trees and shrubs. This is why they can adapt so well to the low light conditions of homes and offices. Though they are mostly tropical in nature, Aspidistra have been known to cope with temperatures as low as −5 °C (23 °F). Despite their leafy appearance, Aspidistra have surprisingly beautiful flowers. You just have to know where to look. 

Flowers are produced at the base of the plant. They are often covered by litter and soil. Despite their cryptic nature, they are nonetheless incredibly beautiful and complex. The flowers are spider-like with a large flattened stigma. They are also the key to identifying different species. Their pollinators are thought to consist mostly of flies, beetles, and the occasional fungus gnat. There is some evidence that some species of Aspidistra are even pollinated by amphipods in the soil. If this is true, it is surely one of the most unique pollinator syndromes ever discovered. 

So, there you have it. One of the most commonly kept and ignored houseplants just happens to be quite interesting. Every plant has an evolutionary and ecological history that has shaped its kind over millennia. It just goes to show you that even the most common houseplants have a story to tell. Think about that next time you come across these growing in a stuffy waiting room. 

Photo Credit: justinleif (http://bit.ly/1srlbwk), scott.zona (http://bit.ly/1wQMdcZ), Phillip Merritt (http://bit.ly/14Rcbph)

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