Drunken Pollinators & Chemical Trickery: Musings on the Complex Floral Chemistry of a Generalist Orchid

There was a time when I thought that all orchids were finicky botanical jewels, destined to perish at the slightest disturbance. Certainly many species fit this description to some degree, but more often these days I am appreciating the role disturbance can play in maintaining many orchid populations. Seeing various genera like Platanthera or Goodyera thriving along trails and old dirt roads, lawn orchids (Zeuxine strateumatica) growing in manicured lawns, or even various Pleurothallids growing on water pipes in the mountains of Panama has opened my eyes to the diversity of ecological strategies this massive family of flowering plants employs.

Of the examples mentioned above, none can hold a candle to the hardiness of the broad-leaved helleborine orchid (Epipactis helleborine) when it comes to thriving in disturbed habitats. Originally native throughout much of Europe, North Africa, and Asia, this strangely beautiful orchid can now be found growing throughout many temperate and sub-tropical regions of the world. Indeed, this is one species of orchid that has greatly benefited from human disturbance. In fact, I more often see this orchid growing in and around cities and along roadsides than I do in natural settings (not to say it isn’t there too). In many areas here in North America, the broad-leaved helleborine orchid has gone from a naturalized oddity into a full blown invasive.

Much of its success in conquering new and often highly disturbed territory has to do with its relationship with mycorrhizal fungi. Like all orchids, the broad-leaved helleborine orchid requires fungi for germination and growth, relying on the symbiotic relationship into maturity. Without mycorrhizal fungi, these orchids could not survive. However, while many orchids seem to be picky about the fungi they will partner with, the broad-leaved helleborine is something of a generalist in this regard. At least one study in Europe was able to demonstrate that over 60 distinct groups of mycorrhizal fungi were able to partner with this orchid. By opening itself up to a wider variety of fungal partners, the broad-leaved helleborine orchid is able to live in places where pickier orchids cannot.

Another key to this orchids success has to do with its pollination strategy. Here again we see that being a generalist comes with serious advantages. Though wasps are thought to be the most effective pollinators, myriad other insects from various kinds of flies to beetles and butterflies will visit these blooms. How is it that this orchid has become to appealing to such a wide variety of insects? The answer is chemistry.

The broad-leaved helleborine orchid is something of a skilled chemist. When scientists analyzed the nectar produced in the cup-shaped lip of the flower, they found a diverse array of chemicals, many of which lend to some incredible insect interactions. For starters, highly scented compounds such as vanillin (the compound responsible for the vanilla scent and flavor of Vanilla orchids) are produced in the nectar, which certainly attracts many different kinds of insects. There is also evidence of some floral mimicry going on as well.

Scientists found a group of chemicals called kairomones in broad-leaved helleborine nectar, which are very similar to aphid alarm pheromones. When released by aphids, they warn nearby kin that predators are in the area. In one sense, the production of these compounds in the nectar may serve to ward off aphids looking for a new place to feed. However, these chemicals also appear to function as pollinator attractants. For aphid predators like hoverflies, these pheromones act as a dinner bell, signalling good egg laying sites for gravid female hoverflies whose larvae gorge themselves on aphids as they grow. It just so happens that hoverflies also serve as important pollinators for the broad-leaved helleborine orchid.

A series of compounds broadly classified as green-leaf volatiles were found in the nectar as well. Many plants produce these compounds when their leaves are damaged by insect feeding. Like the aphid example above, green-leaf volatiles signal to nearby predatory insects that plump herbivores are nearby. For instance, when the caterpillars of the cabbage white butterfly feed on cabbage plants, green-leaf volatiles attract wasps, which quickly set to work eating the caterpillars, relieving the plant of its herbivores in the process. As previously mentioned, wasps are thought to be the main pollinators for this orchid so attracting them makes sense. However, attracting pollinators using chemical trickery can be risky. What happens when a pollinator shows up and realizes there is no plump aphid or caterpillar to eat?

The answer to this comes from a series of other compounds produced in this orchid’s nectar. Few insects will turn down a sugary meal, and indeed, many visitors end up sipping some broad-leaved helleborine nectar. Sit back and watch and it won’t take long to realize that these insects appear to quickly become intoxicated. Their behavior becomes sluggish and they generally bumble around the flowers until they sober up and fly off. This is not happenstance. This orchid actively gets its pollinators wasted, but how?

Along with the chemicals we already touched on, scientists have also found a plethora of narcotics in broad-leaved helleborine nectar. These include various types of alcohols and even chemicals similar to that of opioids like Oxycodone. Now, some have argued that the alcohols are not the product of the plant but rather the result of fermentation by yeasts and bacteria living within the nectar. However, the presence of different antimicrobial compounds coupled with the sheer concentrations of alcohols within the nectar appear to discount this hypothesis and point to the plant as the sole creator. Nonetheless, after a few sips of this narcotic concoction, insects like wasps and flies spend a lot more time at each flower than they would if they remained sober the whole time. This has led to the suggestion that narcotics help improve the likelihood of successful pollination.

Indeed, the broad-leaved helleborine orchid seems to have no issues with sex. Most plants produce a bountiful crop of seed-laden fruits each summer. In fact, it has been found that plants growing in areas of high human disturbance tend to set more seed than plants growing in natural areas. Scientists suggest this is due to the wide variety of pollinators that are attracted to the complex nectar. Human environments like cities tend to have a different and sometimes more varied suite of insects than more rural areas, meaning there are more opportunities for run ins with potential pollinators.

The broad-leaved helleborine orchid stands as an example of the complexities of the orchid family. Few orchids are as generalist in their ecology as this species. Its ability to grow where others can’t while taking advantage of a variety of pollinators has lent to the extreme success of this species world wide.

Photo Credit: [1]

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

How Trees Are Shaping Treehoppers

Photo by Judy Gallagher licensed under CC BY-ND 2.0.

The sessile nature of plants means that they are strongly shaped by their environment. Natural selection is constantly at work on plants but that doesn’t mean that plants don’t shape their environment as well. When I think about the impact of plants on resident animal communities, I am always reminded of a quote by artist Terence McKenna, “Animals are something invented by plants to move seeds around.” Now, I realize that the animal kingdom got its start long before plants came onto the scene but there are many threads of truth to this quote.

Take, for instance, the case of the two-marked treehopper (Enchenopa binotata). This wonderful little insect enjoys a distribution that encompasses much of North and Central America, ranging from Canada down into Panama. Not only do these treehoppers look cool with their intriguing color pattern and that thorny pronatum, but their ecology and evolutionary history is absolutely fascinating as well. The existence of these treehoppes is entirely tied to the trees on which they live and breed. Moreover, while the two-marked treehopper may look like a single species, it is actually a complex of multiple cryptic “species” whose entire identity is owed to their preferred host tree.

Photo by Katja Schulz licensed under CC BY-ND 2.0.

The two-marked treehopper is not a species that moves around the landscape very much. While males will venture out into the environment in search of mates, females tend to live out their whole lives feeding and breeding on the tree upon which they were born. After mating, a female will lay her eggs within the stem of the host tree. The eggs overwinter in a sticky secretion called “egg froth.” This egg froth not only protects the eggs, it is also full of pheromones that signal to other females in the area to lay their eggs near by. The nymphs of the two-marked treehopper are gregarious. There is safety in numbers and the more nymphs hanging out on a branch, the less likely any single individual will be attacked by a predator.

Come spring, as trees begin to break dormancy, eggs laid the previous summer get the cue to hatch as sap begins to flow. Since treehoppers are sap feeders, this signal is essentially a ringing dinner bell. Apparently the specificity of this sap feeding habit is one of the reasons these treehoppers are so specific about their host.

As I mentioned earlier, the two-marked treehopper is not a single species but rather a complex of distinct taxonomic units. All of this cryptic diversity has to do with their preferred trees as each species within the complex feeds and breeds on a specific genus of tree/shrub: Carya, Celastrus, Cercis, Juglans, Liriodendron, Ptelea, Robinia, and Viburnum. Because no two tree species are alike, each has its own phenology. Different trees leaf out and begin growth at different times. Different tree species have different chemicals and nutrients in their sap. Also, different tree species have different wood densities. All of these factors and more have left their mark on the evolution of two-marked treehoppers.

Because females generally don’t leave the trees on which they were born, their offspring will inevitably be born on the same species of tree. This means they will be raised on a diet of the same sap as their mother. As mentioned, different trees produce different kinds of sap, which means that the digestive systems of these insects become highly tuned to their specific host tree. By experimentally moving two-marked treehopper nymphs to different host trees and tracking their development, scientists have also been able to demonstrate that host switching does not work well for the treehoppers. Nymphs raised on species different than the tree on which their eggs were laid do not develop as well or at all. It appears that their specific feeding habits are entirely tuned to the chemical composition of their host sap.

Additionally, the phenology of their host tree life cycle means that species raised on different trees rarely sync up in nature. Some trees force their resident treehoppers to emerge and mate earlier than others and vice versa. Evidence for this was made even stronger by studying these dynamics in the human environment.

The preferred hosts of two-marked treehoppers rarely grow in the same habitats in nature. However, thanks to our gardening and landscaping efforts, it isn’t hard to find these species in close proximity in the human environment. In cases where different host trees are found only a few meters from one another, the specific feeding requirements of each species means that species barriers among different treehopper populations are maintained. However, even before offspring enter into the picture, host trees also seem to have an effect on two-marked treehopper mating habits.

Waveforms of male signals for nine species in the Enchenopa binotata complex based on host tree identity [SOURCE].

Treehoppers are surprisingly musical creatures. Though we can’t hear them without the help of microphones, treehoppers utilize different types of vibrational calls to communicate with one another. This is especially true during mating. Males make repeated vibrations on the stems that the females will then respond to. By studying variations in these calls, scientists have found that two-marked treehoppers living on different trees produce vastly different calls. They key to this appears to lie in the ability of vibrations to travel through wood. Just as different types of wood work well for different types of instruments, the differences in wood density of their host trees affect how their mating calls travel and are eventually perceived. In other words, with a bit of training and some good recordings, you could identify the tree on which a two-marked treehopper lives just by its calls.

The ecological barriers between these insects are maintained no matter how close they are to one another and it is all thanks to the biology of the trees on which they live. Keep an eye out for these wonderful little insects. They are a joy to watch and offer us plenty of examples of evolution in action.

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

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

The Humble Yet Hardy World of Pineappleweed

For me, an obsession with everything botanical came later on in my academic career. I never paid too much attention to plants as a kid. To be brutally honest, I used to find plants boring. I was too busy preoccupying myself with reptiles, amphibians, and fish. However, if there was ever a plant that was an icon of my care-free childhood existence, it would have to be the humble yet hardy pineappleweed, Matricaria discoidea.

Tearing around on playgrounds for most of the summer months, this little member of the aster family was one of the few species that could handle the endless energy of hundreds of rampaging children and thus was one of the only plants I ever paid much attention to. Still, is wasn’t until much later that I took the time to figure out its identity and natural history.

Pineappleweed is native to parts of northeast Asia and northwestern North America. There are some out there who believe this species may have been brought to North America by paleolithic peoples as a food plant. While this remains to be substantiated, there is no doubt that this is one adaptable species. Now nearly global in its distribution, pineappleweed thrives in some of the harshest habitats imaginable for such a small plant. Its tough stem can handle a lot of foot traffic, making it a common sight along roadsides, city walkways, and of course, playgrounds.

Though at first glance it doesn’t look like it, pineappleweed is a member of the daisy family (Asteraceae). It simply lacks the showy ray florets produced by those of its close cousins. Speaking of cousins, pineappleweed is actually a close relative of chamomile (Matricaria chamomilla). What looks like a single yellow flower is actually a disk made up of many individual flowers densely packed into a dome. The blooms are attractive to tiny syphrid flies but it is not quite known if they are effective pollinators or not. Pineappleweed is also an annual and each disk of flowers can produce thousands of sticky little seeds. This is how this species gets around. Its seeds stick to everything from animal fur to shoes and even car tires. Pineappleweed is yet another species that has benefited from the wanton globalization that humans have enacted upon the world. Keep your eye out for it. It isn’t hard to find and it is certainly a plant worthy of closer inspection.

Further Reading: [1] [2]

Deer Skew Jack-in-the-Pulpit Sex Ratios

Photo by Michael Janke licensed under CC BY-ND 2.0.

Deer populations in North America are higher than they have been at any point in history. Their explosion in numbers not only leads to series health issues like starvation and chronic wasting disease, it has also had serious impacts on regional plant diversity. Wherever hungry herds of deer go, plants disappear from the landscape. However, the impacts of deer on plants aren’t limited to species they can eat. Research on Jack-in-the-Pulpit (Arisaema triphyllum) has shown that deer can have plenty of surprising indirect impacts on plants as well.

Though I wouldn’t put anything past a hungry deer, plants like Jack-in-the-Pulpit aren’t usually on the menu for these ungulates. Their leaves, stems, and flowers are chock full of raphide crystals that will burn the mouths and esophagus of most herbivores. Still, this doesn’t mean deer aren’t impacting these plants in other ways. Because deer are congregating in high abundance in our ever-shrinking natural spaces, they are having serious impacts on local growing conditions. Wherever deer herds are at high numbers, forests are experiencing soil compaction, soil erosion, and a disappearance of soil leaf litter (also due in part to invasive earthworms). Thanks to issues like these, plants like Jack-in-the-Pulpit are undergoing some serious changes.

Like many aroids, sex expression in the genus Arisaema is fluid and relies on energy stores. Smaller plants store less energy and tend to only produce male flowers when they bloom. Pollen, after all, is cheap compared to eggs and fruit. Only when a plant has stored enough energy over the years will it begin to produce female flowers in addition to males and only the largest, most robust plants will switch over entirely to female flowers. As you can imagine, the ability of a plant to acquire and store enough energy is dependent on the quality of the habitat in which it grows. This is where deer enter into the equation.

High densities of deer inevitably cause serious declines in habitat quality of plants like Jack-in-the-Pulpit. As leaf litter disappears and soil compaction grows more severe, individual plants have a much harder time storing enough energy each growing season. In places where deer impacts are heaviest, the sex ratios of Jack-in-the-Pulpit populations begin to skew heavily towards males because individual plants must grow much longer before they can store enough energy to produce female flowers. It doesn’t end there either. Not only does it take longer for a plant to begin producing female flowers, individual plants must also reach a much larger size in order to produce female flowers than in areas with fewer deer.

Photo by Charles de Mille-Isles licensed under CC BY-ND 2.0.

As mentioned, seed production takes a lot of energy and any plant that is able to produce viable fruits will have less energy stores going into the next season. This means that even if a plant is able to produce female flowers and successfully set seed, they will have burned through so much energy that they will likely revert right back to producing only male flowers the following year, further skewing the sex ratios of any given population towards males. Interestingly, this often results in more individuals being produced via clonal offshoots. The more clones there are in a population, the less diverse the gene pool of that population becomes.

Without actually eating the plants, deer are having serious impacts on Jack-in-the-Pulpit population dynamics. I am certain that this species isn’t alone either. At least Jack-in-the-Pulpit is somewhat flexible in its reproductive behaviors. Other plants aren’t so lucky. I realize deer are a hot button issue but there is no getting around the fact that our mismanagement of their natural predators, habitat, and numbers are having serious and detrimental impacts on wild spaces and all the species they support.

Photo Credits: [1] [2]

Further Reading: [1]

Bees Bite Leaves to Induce Flowering

Photo by Ivar Leidus licensed under CC BY-ND 2.0.

Imagine spending all winter sleeping underground, living off of the energy reserves you accumulated the previous year. By the time spring arrived and you started waking up, your need to eat would be paramount to all other drives. Such is the case for emerging queen bumblebees. Food in the form of nectar and pollen is their top priority if they are to survive long enough to start building their own colony, but flowers can be hard to come by during those first few weeks of spring.

Spring can be very unpredictable. If bees emerge from their slumber too early or too late, they can miss the flowering period of the plants they rely on for food. By the same token, the plants themselves then miss out on important pollination services. Mismatches like this are becoming more common as climate change continues to accelerate. However, not all bees are helpless if they emerge onto a landscape devoid of flowers. It turns out that, with a little nibble, some bees are able to coax certain plants into flowering.

Over a series of experiments, scientists were able to demonstrate that at least three species of bumblebee (Bombus terrestris, B. lapidarius, and B. lucorum) were able to induce early flowering in tomatoes (Solanum lycopersicum) and mustards (Brassica nigra) simply by nibbling on their leaves. The queens would land on the leaf and make a series of small holes with their mandibles before flying off. The bees did not appear to be feeding on any of the sap, nor were they carrying chunks of leaf when they flew away. Amazingly, the act of nibbling on the leaves in each experiment resulted in earlier flowering times across both species of plant.

(A) Sequential images of a worker penetrating a leaf with its proboscis. (B) A worker cutting into a leaf with its mandibles. (C) Characteristic bee-inflicted damage. [SOURCE]

The results were not minor either. Flowers on bee-nibbled plants were produced an average of 30 days earlier than non-nibbled plants. Amazingly, when scientists tried to simulate bee nibbles using tweezers and knives, they were only able to coax flowering an average of 8 days earlier than non-damaged plants. What this means is that there is something about the bite of a bee that sends a signal to the plant to start flowering. Perhaps there’s a chemical cue in the bee’s saliva. Indeed, this is not unheard of in the plant kingdom. Some trees have shown to respond to the detection of deer saliva, ramping up defense compounds in their leaves only once they have detected deer. More work is needed before we can say for sure.

Through a complex series of experimental trials, scientists were also able to demonstrate that this behavior was the result of pollen limitation rather than nectar. As pollen availability increased both artificially (by adding already flowering plants) or naturally (as time wore on, more plants came into bloom), the leaf biting behavior declined. Such was not the case when only nectar was available. Pollen is a protein-rich food source for bees and is especially important for their developing larvae. By inducing plants to flower early, the bees are ensuring that there will be a ready supply of pollen when they and their developing larvae need it the most.

Considering the role bees play in pollination of plants like tomatoes and mustards, it is likely that this interaction benefits both players to some degree; bees are able to coax floral resources much sooner than they would normally become available while the plants are flowering when effective pollinators are present in the area. These exciting results open yet another window into the multitude of ways in which plants and their pollinators interact. Given that plants have been known to skew the caste systems in eusocial bees, it should come as no surprise to learn that some bees have a few tricks up their sleeves as well.

Photo Credits: [1] [2]

Further Reading: [1]

The Shape-Shifting Star Chickweed

Photo by BlueRidgeKitties licensed under CC BY-ND 2.0.

Star chickweed (Stellaria pubera) has been called North America’s showiest chickweed and I am inclined to agree. Come mid-spring, this lovely woodland plant produces wonderful white flowers that measure about 1/2 inch across and are ringed by five petals so deeply notched that there appear to be ten. Star chickweed’s floral display takes place rather close to the ground on small, fuzzy shoots but as the flowering window for this species begins to close, a change takes place within the plant. By mid-summer, star chickweed will have grown into something completely different.

As mentioned, flowering for star chickweed occurs close to the ground. During this time, its stems don’t elongate more than a few inches and its leaves are broad, blunt, and sessile. Once seed has been set, star chickweed goes through another growth spurt. New stems begin to grow that are much more vigorous in nature than the flowering shoots. They sprout up from the base of the plant and completely over-top spring growth. They can reach heights of nearly 12 inches and produce much thinner leaves. These summer shoots are usually sterile and only in rare instances have flowers been reported.

Star chickweed showing low-growing fertile shoots (front) and taller, sterile shoots (back). [SOURCE]

Star chickweed’s shape-shifting abilities have confused many a botanizer over the last century or so. Because the fertile and sterile shoots look completely different from each other and largely occur at different times of the growing season, some early botanists even went as far as to describe them as different species. Why this plant goes through two distinct growth phases is still something of a mystery but I suspect it has a lot to do with energy reserves.

Perhaps star chickweed has evolved this shape-shifting habit to keep up with changes in surrounding vegetation. Early in the year, the tree canopy above hasn’t completely closed and many of its herbaceous neighbors are still putting on growth of their own. As such, star chickweed probably doesn’t experience as much competition for light early in the season. Of course, conditions on the forest floor change drastically as spring gives way to summer. It could be that the taller, more vigorous sterile shoots are better able to compete for light as the forest fills in around star chickweed.

Another mystery that still has yet to be answered is what triggers the change in growth. A study published back in 1942 concluded changing day length alone could not explain it and suggested it may be in response to rising summer temperatures. However, their experiment was not terribly thorough, leaving such conclusions in the realm of speculation. I kind of like that about nature. There is always a new mystery to uncover, always a deeper understanding to gain.

Photo Credits: [1] [2]

Further Reading: [1] [2]

When is a mushroom not a mushroom? When it is a Maltese mushroom, of course!

Photo by Hans Hillewaert licensed under CC BY-ND 2.0.

Meet Cynomorium coccineum aka the Maltese mushroom. Despite the common name and overall appearance, this is not a fungus. It is indeed a plant. Cynomorium coccineum is a holoparasite. It produces no chlorophyl of its own and relies solely on a host plant for all of its water and nutrient needs. It is said to parasitize the roots of halophytes or salt-loving plants and thus, is most commonly found growing in salt marshes in addition to dry, sandy habitats in coastal areas.

Native to the Mediterranian region and extending into parts of Afghanistan, Saudi Arabia, Iran, and Central Asia, this species is really only ever found during the rainy season. Most of its life is spent underground, emerging only to display its flowers. Only when enough energy has been garnished from the host will this plant throw up these strange flower spikes. As you can tell from the picture, the spikes are jam packed with highly reduced flowers. The flowers give off a scent that has been likened to cabbage. It is thought that flies take up the bulk of the pollination of these blooms.

Photo by Alastair Rae licensed under CC BY-ND 2.0.

Photo by Hans Hillewaert licensed under CC BY-ND 2.0.

As you can probably guess by its strange appearance, the taxonomic affinity of this strange parasite has been the subject of much debate. For a long time, many botanists placed it in the family Balanophoraceae but more recent genetic work suggests it belongs in its own family, Cynomoriaceae. It is the only genus within that family but interestingly enough, Cynomoriaceae is located within the order Saxifragales, somewhere near Crassulaceae, making it a distant relative of stonecrops like sedum. No matter where its located on the tree of life, Cynomorium coccineum is surely one of the strangest plants on Earth.

Photo Credits: [1] [2]

Further Reading: [1] [2]

Alligators Increase Plant Diversity

Photo by mbarisson licensed under CC BY-ND 2.0.

When you think of gardening, alligators don’t readily jump to mind. Hang out long enough in places like the Everglades and that might change. I was only recently introduced to the concept of a “gator hole” and I must say, I was surprised what a quick search of the literature revealed. It turns out that alligators are important ecosystem engineers and do a wonderful job at increasing plant diversity in the wetlands they inhabit.

Throughout southeastern North America, gators change their behaviors with the seasons. During the rainy season, alligators can be found floating in open water or sunning themselves on land. Except when hunting, they don’t seem to do anything with much urgency. Their activity level changes during the dry season when water is in short supply. Gators don’t sit back and let nature take its course. They spring into action and create their own aquatic refuges.

As the surrounding landscape begins to dry, gators will excavate holes or pits in the soggy ground called gator holes. These holes hold onto water when most of the surrounding landscape isn’t. The process of digging a gator hole may seem destructive but it all must be placed in the context of the surrounding environment. Most gator habitat exists in low lying areas. In places like the Everglades, there isn’t much topography to speak of. When a gator excavates a gator hole, it creates variation in both hydrology and soil conditions.

Photo by Anita Gould licensed under CC BY-ND 2.0.

Soils that have built up over time are lifted out of the hole and piled into mounds. Mounded soils are not only rich in nutrients, they also dry at different rates, creating a gradient in water availability. Plants that normally can’t germinate and grow in saturated soils find suitable spots to live up on the soil mounds while emergent aquatic vegetation fills in along the parameter. Plants that normally prefer to grow in deeper water can also establish within the gator hole itself. In the midst of fairly uniform marsh vegetation, a gator hole quickly becomes a hotbed of plant diversity. The differences in vegetation can be so stark compared to the surrounding landscape that some scientists can actually map gator holes using aerial scans simply by measuring the differences in infrared radiation given off by the leaves of all the different plants that establish around them.

Of course, all of that plant diversity has a huge effect on other organisms as well. Gator holes become important areas for various reptiles, amphibians, birds, and so much more. The paths that alligators take to and from their holes even act like fire breaks, changing the way fire moves through the landscape, which only increases the heterogeneity of the immediate area. Fish, though occasionally eaten, greatly benefit from the stability of water levels within a gator hole. All in all, gator holes are extremely important habitats. Not only do they support a high diversity of plants and animals alike, they make places like the Everglades even more dynamic than they already are.

Photo Credits: [1] [2]

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

The Deceptive Ways of the Calypso Orchid

Photo by Murray Foubister licensed under CC BY-ND 2.0.

Behold the Calypso orchid, Calypso bulbosa. This circumboreal orchid exists as a single leaf lying among the litter of dense conifer forests. They go virtually unnoticed for most of the year until it comes time to flower.

In early spring, the extravagant blooms open up and await the arrival of bumblebees. Calypsos go to great lengths to attract bumblebees. The flower is said to have a sweet scent. Also, the lip sports small, yellow, hair-like protrusions that are believed to mimic anthers covered in pollen. Finally, within the pouch formed by the lip are two false nectar spurs. All of these are a ruse. The Calypso offers no actual rewards to visiting bumblebees.

Not just any bumblebee will do. For the ruse to work, it requires freshly emerged workers that are naive to the orchid’s deception. Bumblebees are not mindless animals. They quickly learn which flowers are worth visiting and which are not. Because of this, the Calypso has only short window of time in which bumblebees in the vicinity are likely to fall for its tricks. As a result, pollination rates are often very low for this orchid.

The most interesting aspect of all of this is that the so-called "male function" of the flower - pollinia removal - is more likely to occur than the "female function" - pollen deposition. The reason for this makes a lot of sense in context; male function requires a bumblebee to be fooled only once whereas female function requires a bumblebee to be fooled at least twice.

The caveat to all of this deception is that a single Calypso, like all other orchids, can produce tens of thousands of seeds. Each orchid therefore has tens of thousands of potential propagules to replace itself in the next generation. Despite that fact, the Calypso orchid is on the decline. Habitat destruction, poaching, deer, and invasive species are taking their toll. If you care about orchids like the Calypso, please consider supporting organizations like the North American Orchid Conservation Center.

Photo by Murray Foubister licensed under CC BY-ND 2.0.

Photo Credit: [1] [2]

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

Why are there so few tree species in Europe?

Photo by Susulyka licensed under CC BY-SA 4.0

Take a look at a list of tree species from temperate Europe, North America, and Asia and you will notice a glaring disparity. Whereas North America and Asia are home to something like 1000 tree species each, Europe is home to just about 500 species. Why is this?

The answer may lie partly in the glacial history of the Northern Hemisphere as well as in some quirks of geology. Starting in the late Pliocene, roughly 3 million years ago, the Earth began to cool. As our planet entered into a epoch dominated by massive, continent-wide glaciers, life was responding accordingly.

Historically it was assumed that Europe lost many of its temperate tree species thanks to the east-west orientation of its mountain ranges. As glaciers advanced from the north, species were pushed farther and farther south until they hit physical barriers in the terrain like the Alps. With nowhere to go but up, many species that couldn’t handle either the rate of climate change or the altitude adjustment simply winked out of existence. Fossil evidence from Europe provides plenty of evidence that this region was once home to far more tree species, including relatives of sweetgum (Liquidambar spp.) and tulip trees (Liriodendron spp.) that are still present in North America, and umbrella pines (Sciadopitys spp.), which still exists in Asia. Many temperate tree species in North America and Asia were spared this fate because there were far fewer barriers to successful southern migrations.

This all sounds a bit too simple and indeed, recent studies suggest that it is. Though climate change, glaciers, and mountains certainly played a role in the differential extinction rates of European trees, the story is a bit more complicated than that. It turns out that the European mountain ranges don’t present as impenetrable of a barrier to plant migrations as was once thought. The fact that southern Europe and northern Africa share many similar taxa is proof of this. Instead, the amount of suitable habitat and land area available to trees migrating down from northern Europe may have played an even larger role in the extinction rate of European trees.

Extent of glacial coverage (blue) during the last ice age. Map by Hannse Grobe licensed under CC-BY-2.5

It is a well documented phenomenon in ecology that smaller areas of land support smaller numbers of species. This is the case for Pleistocene Europe. Suitable habitat for temperate tree species during this time would have largely consisted of three peninsulas (Iberia, Italy, and the Balkans) separated by the Mediterranian Sea. Each of these peninsulas boast mountain chains that would have offered small bands of suitable microclimates for temperate tree species to find refuge during glacial advance.

Pushed into tiny pockets of refugia, Europe’s temperate tree species would have been more vulnerable to extinction than tree species in North America and Asia, which had far more suitable habitat available to them in the southern portions of those continents. By looking at which taxa survived and which went extinct, patterns do start to emerge. Tree species that are widespread in Europe today are descendants of trees that were far more tolerant of cooler growing seasons and harsh winters than genera that went extinct. This likely reflects the fact that their ancestors were those species that found refuge high up in the mountains.

Alternatively, present-day Europe also boasts small pockets of what are termed “relictual genera,” which is a fancy way of saying species that were once more common in the past than they are today. These so-called relictual taxa have been found to be far more tolerant of drought than genera that went extinct. This likely reflects the fact that their ancestors found refuge in warmer, low-elevation habitats in southern Europe.

It appears that species on either end of the tolerance curves were the ones that won out in Europe’s extinction lottery. By tolerating either extreme cold or extreme drought, “stress tolerators” were able to not only survive repeated glaciation events, but also provide seed sources for those lineages following glacial retreat.

Only the species that were able to find suitable habitats in southern Europe’s glacial refugia were the ones that were able to recolonize the region after the Ice Age had ended. At this point in time, these are some of the best pieces of evidence we have in explaining the disparity in tree diversity between Europe, North America, and Asia. What’s more, I find disturbing trends in such extinctions because it wasn’t like the glaciers always wiped out species immediately. Instead, many species were able to survive glaciation but were pushed into smaller and smaller pockets of suitable habitat until relatively small disturbances pushed them over the edge.

Today, we humans are changing Earth’s climates at a rate that hasn’t been seen in over 50 million years and all the while we are fragmenting habitats more and more. What is going to happen to species living today in these tiny pockets?

Photo Credits: [1] [2]

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

Standing up for staghorn sumac

I would like you to truly meet staghorn sumac (Rhus typhina). I say "truly meet" because I know many of you probably have some knowledge of this plant already. If your parents were as misinformed as mine growing up, you were probably raised to believe this plant will cause the same kind of contact dermatitis as poison sumac. Not the case! Though they are related, you probably have not come into contact with poison sumac (Toxicodendron vernix) unless you were hiking around in a bog or other high-quality wetland. Even then, poison sumac is not a common species. The point I am trying to make here is that staghorn sumac is not poisonous!

Staghorn sumac should be celebrated. Few trees can grow in such degraded soil like this tree can. In fact, it is most often encountered in roadside ditches and at the edges of farm fields. In the fall their canopy turns a brilliant shade of red. Seeing a large patch of sumac in full fall color rivals even maples for intensity. Because of this, staghorn sumac can make a beautiful landscape tree. It forms numerous clones from underground roots so that it is rare to see just one tree. Take a step back and look at a staghorn sumac population. They seem to always take on a dome-like shape. Their cloning habit is what gives sumac stand their dome-like appearance. Once a single individual becomes established, it sends out suckers in all directions. The farther out you go from the center of the dome, the younger the clones get.

Since all individuals that sprout from the original tree are clones, entire patches are usually either male or female. Female trees are those that produce the characteristic red, fuzzy seed spikes. The seeds are acrid, oily drupes that are low in fat. Because of this they do not readily spoil and thus stay on the tree in perfect condition all through winter and even into the next season. All of this adds up to sumac seeds being some of the most highly sought after late winter survival foods for birds and mammals. When everything else has been consumed or has spoiled, sumac drupes become very important meals. It is estimated that over 100 bird species will consume sumac fruits. Insects also relish this tree. Countless numbers of them feed on the leaves, flowers, and seeds.

Most importantly in this day and age, the dead stems and branches of this plant make perfect nesting sites for our native solitary bees. They have a soft pith that is easily hollowed out to make egg laying chambers. From carpenter bees to mud wasps, you can find dozens of species nesting in a sumac patch.

Finally, a delicious but tart tea can be made from steeping the seeds in cool water. The longer they steep the stronger the tea. In the heat of summer it is quite refreshing. However, you may want to filter it through a coffee filter before drinking to avoid ingesting the multitudes of larvae that feed in and among them.

Listen to Episode 297 about sumacs and sumac relatives!

Further Reading: [1]

A Closer Look at Poison Sumac

Photo by JH Miller and KV Miller licensed by CC BY-NC-SA 3.0

Poison sumac (Toxicodendron vernix). The very name is enough to send chills down the spine. At least where I live, this small tree is a bit of a unicorn, often heard of but never seen. That is, unless you know where to look.

A denizen of high quality wetlands, this species is not often encountered by your average hiker. It has a rather spotty distribution in eastern North America as well. I have heard it been said that the best way to find a poison sumac tree is to trip and fall in a bog. The first branch you grab onto will be that of a poison sumac.

Photo by Freekee licensed by CC0 1.0

All jokes aside, coming across one in the wild can be fun. They are a beautiful tree. A member of the family Anacardiaceae, it resembles North America's other sumacs (Rhus sp.), which often gives those innocuous trees a bad reputation. Like its other cousin, poison ivy (Toxicodendron radicans), poison sumac does produce urushiol. Interestingly enough, humans are said to be one of only a small handful of mammals that are susceptible to this compound. The reaction we have to it is not an inherent property of urushiol. Its effects on humans are the result of an allergic reaction. It is said that poison sumac can produce a much harsher reaction than poison ivy. I am one of the lucky ones who does not seem to be allergic to it, which is good news for me as my first encounter with this plant involved most of my face.

Poison sumac fruits are an easy way to tell this tree apart from other sumacs because they produce white-ish fruits, rather than red. Photo by Brett Whaley licensed by CC BY-NC 2.0

Also like poison ivy, poison sumac produces nutritious fruits that birds are particularly fond of. Migratory song birds, especially those that live and breed in wetlands, are the main seed dispersal agents for this species. All in all, the ecological value of species like poison sumac far outweigh the anxieties we feel about them. It is important not to live in fear of species like this. With a little attention to detail, contact can be avoided. Moreover, because it lives in high quality wetlands, the odds of the average person coming into contact with this tree are relatively small compared to other plants. I can only speak highly of a species like this. I just wish we had more high quality wetlands around where they could grow.

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

Further Reading: [1]

Buckthorns Gone Wild

Colletia paradoxa photo by James Gaither licensed by CC BY-NC-ND 2.0

When I think of the buckthorn family (Rhamnaceae), my mind conjures up images of battling with Rhamnus invasions around the Great Lakes or the amazing diversity of Ceanothus in western North America. Never have my thoughts drifted to the bizarre and wonderful genus Colletia. Native to temperate regions of South America, this strange group of spiny shrubs is certainly worth a closer look.

Though new to me, the genus Colletia has been known to science and horticulture since at least the late 1700’s. Hailing from temperate climates, at least two of the five known species of Colletia have found there way into temperate gardens elsewhere. Who could blame gardeners for their fascination with these shrubs. Close inspection of Colletia reveals surprisingly complex morphological features.

Colletia paradoxa

For starters, those large, thick, leaf-like thorns are not leaves at all. They are flattened extensions of the stem called cladodes. Instead of relying on leaves for most of their photosynthetic needs, the various Colletia instead produce chlorophyll in their stems. The cladodes function in much the same way as leaves in that their increased surface area maximizes photosynthetic potential. It is likely that cladodes are a means of conserving valuable resources for the plant.

Instead of producing vulnerable leaves that are subject to plenty of damage, these shrubs simply utilize stem tissues. Stems don’t need to be regrown year after year and by adorning the tips of the cladodes with spines, the plant is better able to protect its photosynthetic tissues. That is not to say that Colletia produce no leaves at all. Colletia will produce leaves near the base of each cladode, especially on younger tissues. Leaves, however, are deciduous and don’t stick around long enough to do much photosynthesizing.

Colletia ulicina with its red, tubular flowers. Photo by FarOutFlora licensed by CC BY-NC-ND 2.0

The flowers of Colletia ulicina are pollinated by hummingbirds. photo by James Gaither licensed by CC BY-NC-ND 2.0

Colletia are made all the more noticeable when they come into flower. For most species, clusters of lightly-scented, white flowers are produced at the base of the cladodes. For these species, insects are thought to be the predominant pollinators. Such is not the case for Colletia ulicina. This species produces sprays of bright red, tubular flowers along its stems. In the wild, these are pollinated by the green-backed firecrown hummingbird (Sephanoides sephaniodes).

Another interesting aspect of Colletia ecology is that they are all nitrogen fixers. To be fair, the plants themselves don’t do any of the fixing. Instead, they produce tiny structures on their roots called “nodules,” and those nodules house specialized bacteria collectively referred to as actinomycetes. In exchange for carbohydrates produced via photosynthesis, these bacteria fix nitrogen from the air. This extra boost of nitrogen allows Colletia to survive and excel in the nutrient-poor soils they call home.

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

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

The Sinewy American Hornbeam

Photo by Richard Webb licensed by CC BY-SA 3.0

Winter is when I really start to notice trees. Admittedly, I am pretty poor when it comes to tree ID and taxonomy but there are a few species that really stand out. One of my all time favorite trees is Carpinus caroliniana.

Carpinus caroliniana goes by a handful of common names including ironwood, musclewood, and American hornbeam. All of these names have been applied to other trees so I'll stick with its scientific name. Finding C. caroliniana is rather easy. All you have to do is look for its unmistakable bark.

Photo by Rob Duval licensed by CC BY-SA 3.0

With smooth, sinewy striations and ridges, it is no wonder how this tree got the name "musclewood." The wood is extremely close-grained and is therefore very hard, earning it another nickname of "ironwood."They are generally small trees, rarely exceeding a few meters in height, though records have shown that some individuals can grow to upwards of 20 meters in rare circumstances. I hope that someday I will be able to meet one of these rare giants.

Carpinus caroliniana is also an indicator of fairly rich soils. Due to their high tolerance for shade, they are often a tree of the mixed hardwood understory. Their foliage resembles that of the family in which they belong, the birch family (Betulaceae).

Photo by Katja Schulz licensed by CC BY 2.0

The caterpillar of the io moth (Automeris io)

An adult io moth (Automeris io). Photo by Andy Reago & Chrissy McClarren licensed by CC BY 2.0

A multitude of insect species utilize C. caroliniana as a larval food source including the famed io moth. In the spring, male and female catkins are born on the same tree and, after fertilization, they are replaced by interesting looking nutlets covered by leaf-like involucres. The seeds are an important food source for a variety of birds, mammals, and insects alike.

The male flowers of Carpinus caroliniana. Photo by Philip Bouchard licensed by CC BY-NC-ND 2.0

Carpinus caroliniana is a tree I could never get bored with. Not only does it have immense ecological value, it is aesthetically pleasing too. Its small size and shade tolerance also makes it a great landscape tree in areas too cramped for something larger. Why this species isn't more popular in native landscaping is beyond me.

Photo Credits: [2] [3] [4] [5] [6] [7] [8]

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

Himalayan snowball plants and their fashionably functional coats

Credit to CGTN Nature film crew

Hairy plants are both fun and functional. Hairs or trichomes on the leaves of plants can serve a variety of functions. If the plant is growing in a region prone to cold temperatures, it is thought that a dense layer of hairs can function like a wool coat, keeping the plant warm when temperatures drop. This is such a popular idea that it is often assumed rather than tested. For a strange group commonly referred to as Himalayan snowball plants, the truth is a bit more complicated.

Himalayan snowball plants are members of the genus Saussurea, which hails from the family Asteraceae. Though the genus is widespread, the Himalayan snowball plants are confined to high elevation, alpine habitats in central Asia. As you can imagine, life at such altitudes is defined by extremes. Temperatures during the day can skyrocket due to the lack of atmospheric insulation. Conversely, temperatures can take a dive as weather changes and/or the sun goes down. One look at the Himalayan snowball plants tells you that these plants are wonderfully adapted to such habitats. But what kind of advantages does that this coat of hair provide?

Credit to CGTN Nature film crew

Well, research has revealed a bit more nuance to the whole “winter coat” idea. Indeed, it does appear that the furry coat does in fact provide some insulation to the plant. However, most of the warmth appears to come from the dark color of the inflorescence rather than by pure insulation alone. After all, the vast majority of plants do not produce any heat. The flower heads or capitula of these daisy relatives is low in stature. This keeps it out of the way of the coldest winds. Also, they are so deeply violet in color that they can appear black. This is no accident. As anyone can tell you, darker colors absorb more heat and that is exactly what happens with the Himalayan snowball plants.

Another interesting thing to consider is that most of the growth and reproduction in these plants occurs during frost-free periods of the year. Though temperature swings are frequent, it rarely gets cold enough to severely damage plant tissues until long after the plants have flowered and set seed. Moreover, there is some evidence to suggest that the dense coat of hairs may have a cooling effect during periods of intense exposure to sunlight. Their light color may reflect a lot of the incoming radiation, sparing the plant from overheating. Therefore, it appears that the benefit of such a thick coat of hairs has more to do with avoiding temperature swings than it does ensuring constant warmth. By buffering the plant against huge swings in ambient temperature, the hairs are able to maintain more favorable conditions for plant growth and reproduction.

Credit to CGTN Nature film crew

Also, because this area experiences a monsoon season during growth and flowering of Himalayan snowball plants, these hairs may also serve to repel water, keeping the plants from becoming completely saturated. If water were to stick around for too long, it could open the plant up to pathogens like fungi and bacteria. It could also be that by insulating the plant against temperature swings, the hairs also provide a more favorable microclimate for pollinators. Bumblebees are thought to be the main pollinators of Himalayan snowball plants and despite their ability to maintain higher internal temperatures relative to their surroundings, anything that can buffer them as they feed would be beneficial to both the bees and whatever plant they may be pollinating as a result.

Photo Credit: [1]

Further Reading: [1] [2]

Twinflower

Here is a short story about my first encounter with twinflower (Linnaea borealis) back in fall of 2014.

"Summer and occasionally fall" is all I needed to read. So, I had a chance after all. After a few days of sitting in a kayak, musing over various wetland plants, I was excited to get my feet back on solid ground. The Adirondack Mountains offer seemingly endless opportunities for botanizers (and all nature nuts really) to meet new and exciting species that aren't often seen. For me, Linnaea borealis is such a species.

Commonly referred to as twinflower, this small plant is technically a dwarf shrub. In fact, it is a member of the honeysuckle family, Caprifoliaceae. Unlike its larger, more aggressive cousins, twinflower would be an easy plant to miss for most. It behaves much like partridge berry as it ambles over rocks and logs, never leaving the damp forest floor. Out of those who would pay it any mind, even fewer would consider this nondescript plant much to fuss about but those people have never seen this plant in flower.

During the warmer summer months, L. borealis puts on an unbelievable display. Each sprig of stem and leaves throws up a pair of bell-like flowers that will knock your socks off. Each flower is permanently aimed at the ground like tiny lampshades. The flowers are small and dressed in a mixture of white and pink but a large population in full bloom would be impossible to miss. There is something to be said about the beauty of small plants like this. Unlike larger, gaudy flowers, L. borealis forces its admirers to get down on its level to enjoy its full beauty. I like that in a plant.

Twinflower ambling over a rock in the company of some Cladonia lichen.

The genus name "Linnaea" was given to this species in honor of the Swedish botanist, physician, and zoologist, Carl Linnaeus, who invented the binomial nomenclature naming scheme that we still use today. L. borealis has been said to be his favorite plant. As the specific epithet suggests, this species is circumboreal in its distribution. It is found in the northern forested regions of every continent in the northern hemisphere. It can also be found farther south but only at high elevation. These southern populations are disjunct relicts of the Pleistocene Epoch.

Pushed south by advancing ice sheets, boreal species like L. borealis took refuge at high elevation where climates were more similar to the far north. After the glaciers retreated, these populations were able to hang on in small pockets atop mountains. The most interesting thing about this is that L. borealis is not self compatible. It needs genetically different individuals to successfully set seed. In areas where only a small group of individuals represent an entire population, L. borealis has a hard time reproducing sexually. Such populations populations only persist via vegetative cloning. In places like Scotland, this has lead to some concern over genetic stagnation. Throughout the world, at the edges of its range, L. borealis has taken a hit from this genetic stagnation and its range is shrinking. As favorable climates continue to change, the relict populations atop mountains have nowhere to go and thus risk extirpation.

Despite all of this, L. borealis is one tough cookie. If you live where this plant is native, make sure to keep a watchful eye out for it when you are hiking. All too often it is trampled over by unwary hikers. If you are lucky enough to find a patch in bloom, get down on your hands and knees and really get to know this species. You will certainly be happy that you did.

Further Reading: [1] [2]

The Role of Leaf Shape on Insect Herbivory

Plants can defend themselves from herbivores in a variety of ways - thorns, spines, hairs, toxins, etc. - but have you ever considered the role of leaf shape in preventing herbivory? It’s okay if you haven’t because leaf shape rarely, if ever, makes it into conversations of plants defense. A recent experiment from Japan has changed that by demonstrating that leaf shape can actually deter a specialist leaf-rolling weevil.

Meet Apoderus praecellens, a leaf rolling weevil that specializes on a genus of mints called Isodon. To successfully reproduce, female leaf rolling weevils must roll up an Isodon leaf while laying eggs as she goes. The end result is a tiny cigar-shaped, edible nursery chamber in which her larvae will develop. The act of processing a leaf is a complex process.

Isodon trichocarpus Photo by Qwert1234 licensed by CC BY-SA 3.0

The female weevil begins by walking along the margin of the leaf until she reaches the apex. At that point she walks sideways towards the interior of the leaf until she finds the midrib. She then turns around and walks back toward the leaf base again. She repeats these steps several times on both sides of the leaf until she is satisfied. At that point, she will take several bites out of the midrib, which causes the leaf to wilt. The wilted leaf is then much easier to manipulate and thus the rolling process begins.

In the wild, female weevils are well documented on the leaves of I. trichocarpus but not on the leaves of I. umbrosus. This is strange because not only are these plants closely related, they frequently grow in close proximity to one another. Why would the female weevils prefer one over the other? The answer appears to lie in the shape of their leaves.

Isodon trichocarpus produces non-lobed leaves whereas the leaves of I. umbrosus are deeply lobed. When presented with a choice, female weevils did indeed choose to roll I. trichocarpus leaves over those of I. umbrosus. These plants do not differ in their chemical makeup and larvae raised on both species did not differ in their health or development time. Thus, nutritional value or defense compounds don’t explain weevil preference.

Even more amazing is that the preferences seemed to change when I. trichocarpus leaves were cut to resemble the lobed I. umbrosus leaves. It seems that the presence of leaf lobes is the key to whether a weevil decides to lay her eggs or not. The reason for this seems to be the complex leaf inspection behavior outlined above. The deep lobes of I. umbrosus leaves disrupt the female weevils as they carry out their complex inspection process. If the females are interrupted, they rarely progress to the leaf rolling stage.

The researchers are quick to point out that leaf shape in this instance probably didn’t evolve in response to herbivory. Leaf shape is the result of a multitude of selection pressures like light availability, heat, and drought. Still, the fact that leaf shape can also influence herbivore pressure is an interesting piece to add to the puzzle. It is a great reminder that an organism’s niche comprises so much more than simply the abiotic conditions in which it lives. The niche is also the myriad biological interactions each organism undertakes.

Photo Credits: [1] [2]

Further Reading: [1]

Burrowing Birds, Biocrust, and Biodiversity: A Microclimate Story

Nolana humifusa (Solanaceae) Photo by Michael Wolf licensed by GNU Free Documentation License

Peru’s coastal deserts are some of the driest places on Earth. Most of the water they receive comes not from rain but rather fog rolling in off the ocean. These fog-fed habitats are known as Lomas and they support a surprising diversity of plant species. Still, life in the Lomas is no treat so plants growing there need a bit more than a tough disposition to get by. Many components of the Lomas flora rely on favorable microclimates to survive long enough to reproduce. Recently it has been found that a few species of burrowing birds are responsible for creating some of these favorable microclimates.

The beneficial effects of burrowing or “fossorial” animals on plant diversity has many examples in nature. This is especially true in harsh climates. The act of burrowing disturbs the surrounding soil and can expose nutrient-rich soils as well as increase hydrology. However, more than just mammals burrow. As such, researchers wanted to investigate the role of burrowing birds on Lomas plant diversity.

A pair of burrowing owls (Athene cunicularia) Photo by Ron Knight licensed by CC BY 2.0

The birds in this study consist of one owl - the burrowing owl (Athene cunicularia), and two species of miner birds (Geositta peruviana & G. maritima). Instead of nesting in trees, which are few and far between in such arid habitats, these birds nest in the ground. To do so, they excavate burrows. As they excavate, these birds break up the thin biocrust of cyanobacteria that carpets undisturbed stretches of sand. This biocrust is an immensely important component of the local ecology. It stabilizes sandy soils and increases their fertility. It also has a considerable impact on water infiltration, runoff, albedo, and temperature of the soil.

The greyish miner (Geositta maritima)

The coastal miner (Geositta peruviana) Photo by Berichard licensed by CC BY-SA 2.0

Taken together, it is easy to see how large patches of biocrust can either promote or inhibit plant germination and growth. Some species perform well under such conditions while others do not. This is why researchers were so interested in burrowing birds. By breaking up the biocrust and constructing mounds outside of their burrows, these birds are changing the microclimates of the surrounding area. This creates a heterogeneous patchwork of soil types that in turn influence the plant species that can grow and survive.

It turns out, burrowing birds on the Peruvian coast are having considerable effects on local plant diversity. By studying the soil properties around burrows and comparing it to undisturbed soil patches nearby, researchers were able to show that the plant communities living in these areas are in fact different. For starters, despite undisturbed soils having far more seeds in the soil seed bank than burrow mound soils, far more plants germinated and grew on the mounds than in the biocrusts. Also, though the seed bank of the mounds was largely comprised of similar species to that of the undisturbed soils, the seeds of species that produce bird-dispersed berries such as Solanum montanum were more abundant in the mound soil.

Fuertesimalva peruviana (Malvaceae) Photo by Jose Roque licensed by CC BY-SA 3.0

In terms of seedlings, mound soils not only exhibited higher seedling emergence, they also exhibited a higher species richness than the undisturbed biocrust soils nearby. The benefits of growing in the mound soils were most apparent for three plant species in particular: Cistanthe paniculata (Montiaceae), S. montanum (Solanaceae), and Fuertesimalva peruviana (Malvaceae). It appears that these species are much more likely to germinate and survive in and around the burrows than they are in the surrounding landscape. Such a boost to growth and survival, however marginal, means a lot in such a harsh, uninviting landscape.

Even more incredible is how specific burrow microclimates can be. Plants growing on the mounds didn’t do so in a uniform way. Instead, tiny variations in the soil of the burrow mound appeared to make a huge difference for plants. Soils near the entrance of an active burrow are disturbed far more often than soils on the backside of the mound. As such, more plants were found growing on the backside of the mound, demonstrating yet again how slight improvements in favorable microclimates can have astounding impacts on plant survival and diversity.

A. Soil profiles of the studied treatments. B. Landscape of the study area. The lower site of the hills is covered in biocrust except where it is disturbed by birds' burrows (Bioperturbation labeled in the picture). C. Dark cyanobacterial biological soil crust that covers the study site. D. Burrowing owl Athene cunicularia standing on its bioperturbation. [SOURCE}

The reason some plants do much better in disturbed soils over those covered in cyanobacteria biocrust are still not entirely clear. It is likely that some plants simply can’t break through the biocrust as they germinate. It is also possible that the seeds of some of these species simply can’t break through the biocrust to even make it into the soil seedbank. Not only would this cause them to blow around, it also means that they aren’t contacting the soil enough to imbibe water and germinate. Despite containing fewer seeds, the act of digging a burrow may loosen up the soil enough so that seeds are properly buried and thus can maintain good soil to seed contact for long enough to promote germination and growth.

All in all it appears that these three bird species are important ecosystem engineers across the Lomas of the Peruvian coast. By creating a patchwork of different soil properties, these birds are essentially creating a patchwork of different habitats that support different plant species. Take the birds away and it is reasonable to assume that plant diversity would decline. This is yet another important reminder of how interconnected the natural world truly is. It is also an important reminder of why habitat, rather than species-specific conservation efforts should be a much higher priority than it is today. Please, support a land conservation agency today!

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

Further Reading: [1]

An Intriguing Way of Presenting One's Pollen

Photo by Monteregina (Nicole) licensed by CC BY-NC-SA 2.0

Getting pollen from one flower to another is the main reason why flowers exist in the first place. It makes sense then why pollen is often made readily available to pollinators. For many flowering plants, this means directing the pollen-filled anthers outward where they are ready to take advantage of floral visitors. The sunflower family (Asteraceae) does this a bit differently than most. They utilize a technique called secondary pollen presentation.

Though secondary pollen presentation is not unique to the sunflower family, their abundance on the landscape makes it super easy to observe. For the sunflower family, what looks like a single flower is actually an inflorescence made up of dense clusters of individual flowers. Each individual flower is roughly tubular in shape and, oddly enough, the anthers are tucked inside the tube facing the interior of the flower. It may seem odd to hide the anthers and their pollen inside of a tube until you see the blooming process sped up.

Photo by László Németh licensed by CC BY-SA 3.0

The sunflower family actually relies on the female parts of the flower to bring the pollen out from the floral tube and into the environment where pollinators can access it. Members of the sunflower family are protandrous, meaning the male parts mature before the female parts. What this means is that the style of the flower can be involved in presenting pollen before it becomes receptive to pollen. This allows enough time for pollen presentation and reduces the likelihood of self pollination.

As the style elongates within the floral tube, one of two things can happen with the pollen inside. In some cases, the style acts like a tiny piston, literally pushing the pollen out into the world. In other cases, the style is covered in tiny, brush-like hairs that rake the pollen from the sides of the floral tube and carry it out as it emerges. In both cases, the style remains closed until enough time has passed for pollen to be taken away from the inflorescence.

Watch _asteraceae GIF on Gfycat. Discover more Timelapse, aster, awesome, back, background, bloom, cool, flower, ground, grow, lapse, out, relax, slender, slow, time, visuals, white, wood, zone GIFs on Gfycat

After a period of time (which varies from species to species), the style splits at the tip and each side curls back on itself to reveal the stigmatic surface. Only at this point in time is are the female parts of the flower mature and ready to receive pollen. With any luck, much of the flowers own pollen would have been collected and taken away to other plants.

The combination of sequential blooming of individual flowers and protandry mean that members of the sunflower family both maximize their chances of pollination and reduce the likelihood of inbreeding. Add to that their ability to disperse their seeds great distances and myriad defense strategies and it should come as no surprise that this family is so darn successful. Get outside and try to witness secondary pollen presentation for yourself. Armed with a hand lens, you will unlock a world of evolutionary wonders!

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

Further Reading: [1] [2]

A Tiny Passionflower with a Hardy Disposition

Passionflowers barely need an introduction. Who hasn't marveled at the beautiful splendor of their intricate blossoms. Thought largely tropical in their distribution, there are a couple members of the genus Passiflora that have tackled temperate North America. My favorite of these is small and not nearly as gaudy as its cousins but that is kind of what makes me like it so much. Today, I would like to introduce you to the yellow passionflower (Passiflora lutea).

Did I mention this was a small plant? Whereas it can vine itself over surrounding vegetation very effectively, it is by no means a bulky plant. Even more incredible are its flowers. Anyone familiar with the anatomy of Passiflora flowers will be shocked to see all of that detail miniaturized into a yellow-green bloom about the size of your thumbnail. You must be quick to catch these in flower as they themselves are only open for about a day.

As I mentioned above, Passiflora don't come any hardier than the yellow passionflower (except maybe P. incarnata). With a range that extends as far north as Pennsylvania, this lovely little vine can handle winter temperatures as low as −30 °C (-22 °F)! This has earned it the designation of the northernmost species of Passiflora. Even then, I have heard reports of people growing this hardy little plant farther north in Canada.

Pollination for this species works in much the same way as it does for the genus as a whole. The flowers require an insect large enough to contact the peculiar arrangement of anthers and stigmas. The strange yet beautiful filaments that ring the center of the bloom are collectively referred to as the corona and it is believed that these guide insects to the nectar and thus into perfect position for pollination.

By far the most peculiar aspect of this plant is the relationship it has formed in part of its range with a tiny bee aptly named the passionflower bee (Anthemurgus passiflorae). Native from central Texas to North Carolina and north to Illinois, this tiny black bee is the only member of its genus. What's more, it absolutely requires the yellow passionflower for its reproduction. It feeds its larvae solely on pollen from the yellow passionflower. If that wasn't strange enough, despite its highly specific foraging habits, the diminutive size of the bee has led experts to believe that the passionflower bee contributes very little in the way of pollination for the plant.

Further Reading: [1] [2]