Orchid Booby Traps

Pterostylis coccina. Photo by BerndH licensed under CC BY-SA 3.0

Looking as if they have escaped from some sort of modern art exhibit, the flowers of the various greenhood orchids (genus Pterostylis) are as complex as they are beautiful. Native throughout Australia, New Zealand, New Guinea, New Caledonia, and Indonesia, greenhood orchids number around 300 species, all of which are terrestrial. As more attention is paid to their ecology, we are also discovering that many of those 300 species utilize seriously complex trickery to increase their chances of being pollinated.

Pterostylis metcalfei. Photo by Geoff Derrin licensed under CC BY-SA 4.0

Though they vary in shape, size, and color, the flowers of greenhorn orchids roughly conform to a similar morphological theme. The dorsal sepal and two lateral petals are fused, forming a good-like structure, hence the hooded reference in the common name. On the front of the flower, the two lateral sepals also fuse near their base and taper into two points or wings at the top that give the flowers even more charisma. The whole structure forms a sort-of pitfall trap around the sexual organs. In many species, the lower petal or labellum often sticks up and out of the mouth of the floral tube and is frequently dressed in hairs or other protuberances.

Pterostylis turfosa. Photo by Geoff Derrin licensed under CC BY-SA 4.0

Greenhood orchid flowers are true marvels of evolution. Not only are they structurally complex, they are also painted in various shades of greens, whites, reds, and browns. Of course, all of this intricate beauty serves a single function for these orchids, sex. Essentially, greenhood orchid flowers are pollinator booby traps. Like so many other orchids, the greenhoods are tricksters, luring in their pollinators with the promise of food or even sex but offering nothing in return. Though we still have a lot to learn about pollination in this genus, what evidence we have compiled indicates that the promise of sex is the main ruse the greenhoods employ.

Pterostylis baptistii. Photo by Melburnian licensed under CC BY 3.0

The prevalence of male insects visiting the flowers of many greenhood species tells us these orchids achieve pollination via sexual deception. Lured in by scents that precisely mimic the pheromones of receptive female insects, the males land on the flower and begin searching for a mate. They inevitably begin exploring the labellum, which leads them down into the floral tube. At a certain point in their journey, the male insect will reach a tipping point on the labellum. Like an unbalanced seesaw, the labellum snaps backwards as the insect’s weight shifts, slamming the visitor into the column where it comes into contact with the reproductive organs.

The whole process seems very alarming for the unsuspecting victim. The male insect will struggle quite a bit before it finds a single escape route provided by the floral anatomy that ensures both pollen acquisition and deposition. Experiments have shown that this lever mechanism can be repeated upwards of 3 times within a few hours, so each flower has at least a few attempts to get the process right.

Pterostylis alpina. Photo by Melburnian licensed under CC BY 3.0

So, who are the insects that fall victim to the greenhood ruse? It turns out that its mostly small flies like fungus gnats and mosquitoes. The few detailed investigations that have been made into the pollination syndromes of these orchids has revealed surprisingly complex and often species-specific relationships between the plants and their pollinators. This makes sense from a chemical standpoint. The mating pheromones of one species of fly or mosquito are unlikely to attract males of different species. As such, the orchids trickery only works on one or possibly even a couple closely related species. Still, many mysteries abound in this diverse and widespread group of orchids and it will take a new generation of curious botanists and ecologists to uncover them.

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

Dendrologist Squirrels

Gary Cobb licensed under CC BY-ND 2.0

I find it fun to watch squirrels frantically scurrying about during the months of fall. Their usually playful demeanor seems to have been replaced with more serious and directed undertones. If you watch squirrels close enough you may quickly realize that, when it comes to oaks, squirrels seem to have a knack for taxonomy. They quickly bury red oak acorns while immediately set to work on eating white oak acorns. Why is this?

If you have ever tried to eat a raw acorn then you may know the reason. They are packed full of bitter tannins that quickly dry up your mouth and leave an awful after taste. Tannins are secondary chemicals that plants manufacture for protection. Tannins bind to proteins and keep them from being easily digested. This is how leather is made. When you tan a hide you are literally dousing it with tannins that bind to the proteins and keep them from rotting.

Back to the squirrels. The reason they seem to be choosy about how they deal with acorns all comes down to tannins. They bury red oak acorns because acorns in the red oak group have the highest levels of tannins. This is because red oak acorns do not germinate until spring. They have high levels of tannins to fight off fungi and other pathogens over the long, dreary winter. Thus, red oak acorns store better. White oaks germinate in the fall, using a long taproot to pull them into the soil. Because of this, white oaks don't have to dump as much tannin into their acorns. The squirrels seem to know this and simply bite out the white oak embryo before it can germinate. White oak acorns get eaten much sooner than reds because they simply do not keep as long.

There is also evidence that oaks and squirrels have struck a balance. Oaks do rely on squirrels as well as birds like jays to disperse their seeds. These critters can't remember where they cached all of their seeds so some are bound to germinate. What some researchers have found is that oaks place more tannins near the embryos in the acorn than they do at the tips. Why is this? As it turns out, acorns that have had their tips bit off can still germinate as long as their embryo remains unharmed. It is believed that this satisfies squirrels and jays enough to keep them from downing the entire acorn every time. Knowledge such as this puts a whole new spin on backyard ecology.

Photo Credit: Gary Cobb licensed under CC BY-ND 2.0.

Further Reading: [1]

The Overcup Oak

Photo by Bruce Kirchoff licensed under CC BY 2.0

I sure do love me a good oak. Moving to the Midwest of North America has given me the opportunity to meet many new oak species. One oak that has captured my attention in recent years is the overcup oak (Quercus lyrata) whose both common and scientific names first attracted me to this wonderful tree.

Let’s start by looking at the scientific name of this species. The specific epithet “lyrata” was given to this tree because its leaves are said to resemble a lyre. Having no familiarity with popular instruments of Ancient Greece, I had to look this one up. Personally, I have a hard time seeing the resemblance in most leaves. Perhaps this is because the leaves on any given tree can be highly variable in both shape and size depending on both where they are positioned in the canopy and where the tree itself is rooted.

Photo by Bruce Kirchoff licensed under CC BY 2.0

The name “overcup” comes from the fact that the caps of each acorn nearly encompass the entire seed. It is neat to see a mature acorn of this species as they appear to be immature at all stages of development. The odd morphology of these acorns has everything to do with where these trees grow in nature and the way in which they manage seed dispersal.

Photo by Bruce Kirchoff licensed under CC BY 2.0

Overcup oak is one of the most flood tolerant oaks in all of North America. In fact, it most often grows in around wetlands and in floodplains throughout south-central portions of the continent. As such, this species has evolved to tolerate and take advantage of periodic flooding from one year to the next. Not only can mature trees handle weeks of having their roots and trunks completely submerged, the overcup oak also utilizes flooding as a means of seed dispersal.

The cap that covers each seed is very corky, which causes the acorns to float. This is good news for the seeds as young trees have a hard time making a living in the shade of their parents. Historically, floods would pick up and move overcup acorn crops and, with any luck, deposit the acorns in a new floodplain where disturbance has cleared enough spots in the canopy for the acorns to germinate and grow into vigorous young saplings.

USGS/Public Domain

Speaking of germination, overcup oaks are unique among the white oak tribe in that their seeds exhibit a prolonged dormancy. Normally, acorns of the various white oaks germinate in the fall, not long after they were shed from the trees above. However, living in areas prone to flooding would make germinating at that time of year a risky endeavor. As such, overcup oak acorns lay dormant for months until some environmental cue(s) signals enough time has passed.

Overcup oak is also extremely intolerant of fires. Even modest sized burns can severely damage or kill all but the largest individuals. Normally, the forests in which these trees grow are too wet to produce large fires but prolonged droughts and altered flood regimes can change those dynamics to such a degree that large swaths of overcup oak can be killed.

In fact, altered flooding regimes are one of the biggest threats facing overcup oaks in their native range. Because we have dammed, diverted, and channeled so many waterways in North America, the floods that once maintained overcup oak habitats have changed in a big way. Without regular flooding to disperse their seeds and reduce competition from the canopy above, overcup oaks are having a much harder time regenerating. Saplings gradually dwindle in the shade of their parents and, where rivers do continue to flood, these events are often much more severe than they were in the past. Saplings that aren’t tall enough to rise above the floodwaters eventually drown. Overcup oak may be tolerant of flooding but it is by no means its preferred way to live.

Despite these challenges, overcup oak is still a prominent member of seasonally flooded forests throughout its range. It is a magnificent species well worth spending the time to become familiar. It can also make an excellent specimen tree in all but the driest of south-central North American soils. Also, because it is an oak, this incredible species is also chock full of wildlife value, making it an important component of the ecology wherever it is native.

Photo Credits: Bruce Kirchoff [1] [2] (Licensed under CC-BY), U.S. Geological Survey, Chhe, USDA

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

Learn to Love Bluevine

I will admit that it took me a bit to figure this plant out. At first I thought I was looking at a significant bindweed infestation. These heart shaped leaves were twinging all over our fence. Then it flowered and I realized that this was no bindweed. This mysterious vine was none other than bluevine (also commonly called honeyvine, Cynanchum laeve)

Believe it or not, this is a species of milkweed. Though not in the genus Asclepias, it nonetheless belongs within the same family (Apocynaceae) and is close enough in relation to function as a host for species such as the charismatic monarch butterfly.

Mention this in many of the native plant groups and you are bound to be met with resistance. Because this species can be weedy, many people seem to want to overlook its value as a food source for monarch caterpillars. There is even scientific evidence to suggest that there are no significant differences in fitness and survival among caterpillars raised on either common milkweed or bluevine. The authors of one study even make the conclusion that,

“Given the abundance of honeyvine milkweed in the east-central United States, this species may be a more important host plant for the monarch than has been generally recognized.”

The biggest problem people seem to have with bluevine is that it can be very aggressive in disturbed soils. In many places it is considered a serious agricultural pest. Like its milkweed cousins, its seeds erupt from pods and are born on light, feathery filaments. Because of this they can travel great distances on the slightest breeze. They germinate readily and, once established, the plant can regrow from rootstock.

Regardless of where you stand on bluevine, there is no denying that it is an interesting species. Its flowers are packed into clusters and smell heavily of honey. They are primarily visited by small solitary bees. As is typical of the family, bluevine produces some serious chemical defenses. As such, it is generally ignored by mammalian herbivores but is readily consumed by many of the other native milkweed specialists in North America. So, I urge you to consider giving bluevine a chance. You may grow to love its hardy disposition and its great ecological value.

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

The Amazing Pollination Strategy of Bellflowers

Harebell (Campanula rotundifolia). Photo by H. Zell licensed under CC BY-SA 3.0

Pollination is the key to success for any sexually reproducing plant. The movement of pollen grains from one flower to another is a way of ensuring genetically diverse offspring. Plants have many different ways of maximizing the chances that their pollen will end up on an unrelated individual rather than their own flowers. There is no one size fits all strategy after all. I only recently learned of an incredible pollination mechanism that is used by bellflowers in the genera Campanula and Campanulastrum and it involves moving hairs.

The bellflowers utilize a strategy called secondary pollen presentation to minimize the chances of pollinating their own flowers. What this means is that pollen is locked up in the anthers until the style elongates and drags the pollen with it. The process is aided by the fact that bellflowers styles are covered in hairs that collect the pollen as it elongates. Essentially, the style acts like a tiny pipe cleaner, emptying the anthers of the pollen they contain. The stigma itself will not become receptive to pollen until most of its own pollen has been removed. But how does the plant “know” when this happens? The key to this lies again in those hairs.

(1) Immature stamen surround the style; (2) elongation of the style by which the anthers dehisce and pollen grains are swept on the stylar hairs of the immature style; and (3) further outgrowth of the style, anthers are withered. [SOURCE]

The hairs that cover the style are sensitive to touch. When an insect lands on the style and begins collecting pollen, its movements send a signal to cells at the base of each hair that causes a change in how they store water. When triggered, these cells expel water, causing them to shrink. As they shrink, the hairs are gradually drawn down into pockets or cavities within the style. As they do this, pollen either drops off or is taken down into the cavities with the hairs.

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Pollen collecting hairs on 1) Campanula barbata; 2) Campanula kremeri; 3) Campanula dichotoma; 4 - 6) Cavities in which pollen collecting hairs have retreated. [SOURCE]

Only after the hairs have retracted will the stigma become receptive to pollen. In doing so, the plant minimizes the chances that its own pollen will end up on the receptive stigma. That is not to say this works 100% of the time. Research has found that the rate at which the hairs retract is a function of how often the flowers are visited. Flowers that receive numerous pollinator visits in a short period of time will retract their hairs much faster than plants that receive fewer visits. If a flower is not visited, the style will eventually become receptive regardless if pollen has been removed or not. In a pinch, even self-pollination will ensure a continuation of that individuals genes. Not ideal, but this backup plan certainly works, especially for annual species like American bellflower (Campanulastrum americanum) that usually have only one season for reproduction.

American bellflower (Campanulastrum americanum) with its elongated, receptive style. Photo by Joshua Mayer licensed under CC BY-SA 2.0

I have always enjoyed bellflowers. They are beautiful plants with lots of ecological value. Learning about this interesting and surprisingly complex pollination mechanism only makes me appreciate them more. I only wish you could see the process happening with the naked eye.

Photo Credits: [1] [2] [3] [4] All images licensed under CC BY-ND 2.0.

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

The ancestors of many Hibiscus cultivars are in trouble

The genus Hibiscus contains some of the most widely recognized and venerated plants on Earth. Take a trip to any garden center and nursery and you are almost guaranteed to find numerous brightly colored Hibiscus cultivars. No doubt many of you reading this probably have one growing in or around your home. For as common as these cultivars are, most of the species that were involved in producing them are either critically endangered or feared extinct in the wild.

Many of the common tropical Hibiscus cultivars you are likely to encounter involve Hibiscus rosa-sinensis and around 10 distinct species hailing from either one of the Mascarene islands in the Indian Ocean or one of the numerous islands in the central and south Pacific. All of these plants belong to a subgroup within the mallow family known scientifically as Lilibiscus. I won’t bore you with the taxonomic details but what is important to know is that, despite their wide and often non-overlapping distributions, members of this group readily hybridize with one another. It’s this penchant for hybridization that has made them so popular with plant breeders over the centuries.

Hibiscus rosa-sinensis by B.Navex licensed under CC BY-ND 2.0.

In fact, the ease with which these plants are cultivated and bred has obscured the origins of the aforementioned Hibiscus rosa-sinensis. Today, this lovely red mallow grows wild throughout many regions of the Asian continent, however, experts believe that many of these populations represent “escapes” from cultivation. This species has enjoyed so much popularity over the years that no one is quite sure where it originated. Sadly, the same cannot be said for its relatives.

Islands both big and small are metaphorical playgrounds for evolution. This is why islands often boast species of both plant and animal that are found nowhere else in the world. Unfortunately, many of the factors that make islands such hot spots for evolution also make them hot spots for extinctions. Isolation, limited land area, and stochastic events combine to make it all too easy to lose island flora and fauna for good. Add humans into the mix and things get even worse. Humans have been the cause of countless island extinctions ever since our species began island hopping.

The critically endangered Hibiscus fragilis. By Wendy Strahm licensed under CC BY-ND 2.0.

For the case of these 10 members of Lilibiscus, a human presence on their islands of origins has been devastating. Habitat loss due to farming and development and the introduction of invasive species have all but wiped out most populations. For species like Hibiscus fragilis, an endemic of Mauritius, their numbers have been reduced to only a small handful of plants in the wild. Other species like Hibiscus storckii, an endemic of Fiji, were thought to be completely extinct until a few plants were rediscovered. It would seem that after the initial collections were made and brought into cultivation, no one gave these plants much thought. Forgotten, they dwindled in numbers until few, if any, remained.

As if things weren’t already bad for these rare Hibiscus species, humans are adding yet another nail in the coffin for many of them - hybridization. Because Hibiscus are so popular as garden plants, cultivars are commonly planted in gardens wherever climates allow. As I mentioned above, members of the Lilibiscus group readily hybridize with one another. Whereas cultivars are guided by human intervention, that doesn’t mean they need humans to mix their genes. If a cultivar is planted in the proximity of a wild species, there is nothing stopping pollinators from visiting and exchanging pollen with both plants.

Hibiscus storckii was once thought to be extinct until a few plants were rediscovered. BY Jeff Delonge licensed under CC BY-ND 2.0.

If a hybrid cultivar picks up new genes from its wild relatives, no big deal. Either those seeds will never be left to germinate or, if they do, a surprising new variety could be made. Things aren’t so innocuous when gene flow happens in the other direction. One of the biggest threats to the conservation of species like H. fragilis now comes from hybridization with garden Hibiscus. Cultivars are not selected for their ability to thrive in the wild. They are bred and selected for large, showy flowers and a prolonged blooming period. These are not good traits for a wild species with a very specific niche. As the remaining wild H. fragilis are swamped with hybrid genes from cultivars growing in nearby gardens, their offspring no longer contain the characteristics that makes this species unique. One or two hybrids every now and then is probably not an issue, but if those hybrids survive and flower, the stability and fitness of that population will gradually decline as repeated backcrossing occurs.

These issues are not restricted only to the species mentioned above. The tropical cultivars we know and love represent a hybridization complex of Hibiscus species such as H. arnottianus, H. boryanus, H. denisonii, H. genevii, H. kokio, H. liliiflorus, and H. schizopetalus. Nearly all of these species are suffering similar fates in their native range. However, there is a silver lining to all of this. Because Hibiscus often lend so well to cultivation, conservationists have been able to step in before some species are lost forever. Seeds have been collected for both seed banking and germination trials, cuttings have been taken and grown into clones as a means of preserving what genetic diversity remains, and botanical gardens around the world are now adding many of these species to their living collections.

Though the future is not certain for many of these plants, it is certainly looking much better than it was only a few decades ago. While human activity has caused most of these problems, our efforts are now critical in reversing at least some of the damage that has been done.

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

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

Desert Mosses That Live Under Rocks

Syntrichia caninervis growing in both soil surface and milky quartz. [SOURCE]

To be accused of living under a rock is generally not a good thing in today’s society. That is, unless you are a moss living in the Mojave Desert. By setting up residency under milky quartz, a few Mojave mosses are able to find much more favorable growing conditions than they would in the surrounding desert environment.

Microclimates are extremely important, especially in harsh environments like the Mojave. By providing conditions that are ever so slightly better than ambient conditions, microclimates can increase the amount of habitat available, which can lead to greater biodiversity overall. That is exactly what is going on beneath milky quartz in high elevation habitats of the Mojave Desert.

Tortula inermis (white arrow) and S. caninervis (black arrow) growing in a milky quartz. [SOURCE]

While dabbling in a bit of mineral appreciation, bryologists from the University and Jepson Herbaria at UC Berkeley discovered bright green moss growing under some chunks of quartz. Whereas moss growing on the surface of soil and rocks throughout the region were dark, dry, and dormant, the moss growing under quartz was green, lush, and growing. This observation launched a series of experiments to better understand how milky quartz may be providing more favorable microclimates for some desert mosses.

By measuring the conditions under chunks of milky quartz and comparing it to that of the surrounding landscape, researchers found that these minerals do indeed provide mosses with much more favorable conditions. Moreover, the benefits to living under milky quartz are numerous, offering many advantages to resident mosses.

For starters, milky quartz serves as a buffer against large swings in temperature. Deserts are known for being extremely hot but they can also be extremely cold. Sandy soils may heat up very quickly when the sun is out but, by the same logic, they also cool extremely quickly as soon as the sun sets. Rapid swings in temperature can be very harmful to plants so anything that can buffer such swings is generally a good thing. That is exactly what milky quartz does. As the sun rises in the sky, it takes milky quartz longer to heat up than the surrounding landscape, which means the environment directly underneath stays cooler for longer. Similarly, once warmed by the sun, milky quartz takes longer to cool down as the sun sets. As such, the environment directly underneath doesn’t cool down as quickly. By monitoring temperatures over the course of a year, it was found that temperature swings under the quartz were buffered by an average of 4°C (7°F) compared to that of the surrounding environment.

Tortula inermis was more likely to be found growing under quartz at high elevations. [SOURCE]

Though widespread in the Mojave, Syntrichia caninervis nonetheless grows better under quartz. Photo by John Game licensed under CC BY 2.0

Another benefit to living under quartz involves humidity. Not only are deserts hot, they can also be very dry. The Mojave is certainly no exception to this rule as it is considered the driest desert in North America. A lack of water can be troublesome for mosses. Because they lack roots and a vascular system, mosses rely on osmosis for obtaining the water they need to grow and reproduce. They also lose water and dehydrate quickly. For individuals growing exposed to the elements, this means drying up and going dormant. Mosses simply can’t grow when water isn’t around. By monitoring the relative humidity under milky quarts, researchers found that the undersides of milky quartz were twice as humid as the surrounding landscape.

Thanks to this increased humidity, mosses living under milky quartz are able to hold onto water for much longer than mosses growing on exposed soil. This has both short and long-term consequences for moss growing seasons in this harsh desert ecosystem. Increased humidity under milk quartz prolongs the moss growing season much longer than that of their exposed neighbors. In support of this, the researchers found that mosses growing under milky quartz also grew longer shoots. Longer shoots also means more water storing capabilities, which very well could lead to a positive feedback loop between humidity, growing season, and moss health.

(A) Box plot of hypolithic and soil surface S. caninervis shoot length. (B) An S. caninervis shoot fromunder quartz. (C) An S. caninervis shoot from the soil surface. [SOURCE]

Finally, milky quartz may actually protect resident mosses from the blistering rays of the sun. Growing at high elevation means much more exposure to the power of the sun. When fully exposed, desert mosses will often pump their tissues full of pigments like carotenoids, anthocyanins, and flavonoids, which act as sunscreens, protecting their sensitive tissues from UV damage. Even so, exposed mosses can suffer greatly from sun damage and, while dormant, have no means of repairing said damage.

By monitoring the light environment directly under milky quarts, researchers found that, depending on the size of the rock, light transmittance is reduced down to anywhere between 4% and 0.04% of full exposure. Moreover, the crystalline structure of milky quartz is such that it may actually filter out both UV-A and UV-B radiation, thus further reducing the harmful effects of the sun. In fact, mosses growing under milky quartz were found to produce far less sunscreen pigments than their exposed neighbors. If they don’t have to protect themselves from the blistering sun, it appears they don’t waste the energy on such pigments. While a reduction in light may sound bad for a photosynthetic organism, it would appear that the mosses in this study are well adapted to photosynthesizing at lower light levels.

In effect, milky quartz acts like parasols for desert mosses. Just as we like to sit under umbrellas at the beach, these desert mosses find much more favorable growing conditions under milky quartz. While none of the mosses in the study are restricted to growing under quartz, those that do experience multiple measurable benefits that increase their growing season in this largely unforgiving desert ecosystem.

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

Further Reading: [1]

Curly Cucurbits

I’ve grown to really appreciate cucurbits (family Cucurbitaceae) in recent years. From their ambling/climbing habit and often delicious fruits to their beautiful flowers and intimate relationships with a few native bees, this family has a lot to offer. Of course, there are few better ways to get to know plants than by growing them in and around your home and, at least at our place, this summer will go down in history as the summer of the gourd. We are currently growing a handful of species and cultivars and I get a great deal of enjoyment out of watching them grow up the trellis we have provided.

As they climb, cucurbits send out long, thin tendrils (which are actually modified stems) that grab on and wind around any surface they touch. This happens surprisingly quick too. Within only a few minutes of touching a surface, individual tendrils will begin to wind themselves around it. This phenomenon has fascinated people for centuries. I don’t doubt it amused the indigenous cultures that first began cultivating them for food and that amusement continues till this day. Do a web search for cucumber tendrils and you will find countless pictures and blogs showcasing this wonderful anatomical habit.

Despite all the attention, the mechanisms behind this behavior have largely remained a mystery until quite recently. We have known that the initial curling of the tendril is induced by touch. As soon as the cells within the tendril sense contact with a surface, the signal is sent to begin curling. But how do they curl so quickly?

The key to this behavior lies in a two-layered band of specialized cells that run the length of the tendril. Once the signal that the tendril has touched an object has been received, these bands swing into action. One layer of cells will immediately begin to expel water, causing them to contract. Meanwhile, the other layer of cells becomes increasingly stiff and lignified. This creates tension along the length of the tendril, causing it to bend. Oddly enough, this doesn’t happen in the same direction. Take a close look at the tendrils on a cucumber or squash vine and you will notice that each tendril curls in two different directions, separated by a kink or “perversion” (as it is known in the literature) in the middle. This is because the layer of cells on the band that shrinks is different whether you are near the tip or near the base of the tendril.

As many of you reading this are already well aware, the tendrils help to secure the plants as they climb. However, the story is much more interesting than simply anchoring the plants in place. The curling of the tendrils is extremely important when it comes to structural support. If the tendrils did not curl, the plant would be anchored in place with very little wiggle room. As big gusts of wind cause the plant to thrash to and fro or a heavy limb comes crashing down from above, a straight tendril would be far more likely to break under the strain. By adding those opposite twists, the tendrils are able to flex a lot, providing enough movement to keep them from breaking under stress.

If you watch how the tendrils develop over time, their amazing structural support gets even cooler. When stretched, a metal spring looses a lot of its springy-ness. This is not the case for cucurbit tendrils. When stretched, they not only return to their original shape, they curl even tighter. This way, the plant is able to secure itself with varying intensities, allowing for fine tuned adjustments to its structural support. The amount of curling also changes with age. Older tendrils tend to curl more tightly than younger tendrils, especially under strain. As the plant grows, older portions of the stem secure themselves much more strongly via their tendrils. Alternatively, the younger growing portions of the stem need to be a bit more flexible as they anchor themselves to whatever they are climbing on.

So there you have it. The aesthetically pleasing, curly tendrils of your cucurbits serve a very important function in the growth of the plant. Without them, these plants would not only have a hard time climbing, they would also be knocked down by every minor disturbance. The key to their success as vines lies in highly modified stems with an intriguing band of specialized cells that provide them with a physically sound anchoring mechanism.

Learn more in this video:

Further Reading: [1] [2]

What's the deal with nodding flowers?

While working in the garden the other day, I noticed that some of the nodding onion (Allium cernuum) we planted last year had finally come into bloom. I must have spent the good part of an hour watching bees pay a visit to their downward pointing flowers. I have seen a lot of onion species in bloom before, but this particular native is the only one that I know of personally that orients its flowers facing the ground. This got me to thinking about floral orientation. A lot of plants produce flowers that face the ground but many more do not. Why is there such variety among the orientation of flowers?

As always, I hit the literature. It turns out, many scientists have set out to investigate the function of floral orientation. What immediately stuck out to me is just how many different flowering plant lineages boast species whose flowers face down rather than out or up. I knew instantly that with so much variety in lineage, habitat, and pollination strategies, the answer wasn’t going to be simple or straight forward. Indeed, each investigation I read about seemed to end in a slightly different conclusion. Still, there were enough patterns among the results and conclusions to make some general statements about the subject.

The nodding flowers of the Michigan lily (Lilium michiganense)

We often find plants with downward facing flowers in harsh climates. Harsh can mean a lot of different things depending on the plant and region in question but take, for instance, the case of the genus Cremanthodium. This interesting group of asters resemble sunflowers in the basic appearance of their flowers but the plants themselves are vastly different in overall growth habit. Many hail from alpine environments in Asia and possess a short stature and flowers that face the ground instead of the sun. Research on the reproductive habits of these plants has revealed that the downward orientation of their flowers helps protect the sensitive reproductive parts from solar radiation and rain.

Growing at high elevations exposes these plants to lots of UV radiation and plenty of storms. If flowers were to orient towards the sky, rain could wash away pollen and UV radiation could really hinder successful reproduction. By facing the ground, the flowers are able to avoid these potentially harmful effects altogether. Similar results have been found for other members of the aster family in the genus Culcitium growing in alpine habitats in the Andes. Here again we see that downward pointing flowers help protect the sensitive reproductive parts from rain, snow, and too much sun.

The recently described Cremanthodium wumengshanicum growing at elevation in Yunnan, China. [SOURCE]

However, its not just the elements that have selected for downward pointing flowers. As you can probably imagine, pollinators also play a role in floral orientation. While watching bee visit our nodding onions, I noticed that they seem to be much better able to land on and collect pollen and nectar from downward pointing flowers than any of the flies I see attempting visits. Indeed, floral orientation can have a massive impact on what kinds of pollinators are able to effectively visit a flower.

A great example of this can be seen in members of the genus Zaluzianskya. Some species present their flowers horizontally or vertically while others present their flowers facing the ground. By comparing the visitors that frequent each species, researchers found that orientation matters. Upright or horizontally facing flowers were mostly visited by hawkmoths. Hawkmoths hover while they feed, which means they have a much harder time visiting downward facing flowers. By presenting their flowers in different orientations, the various species of Zaluzianskya ensure that only specific pollinators are able to access their rewards and thus achieve pollination. As such, upright, horizontal, and downward flowering species remain reproductively isolated from one another. Similar results have also been found in genera such as the afore mentioned Culcitium as well as some Commelina and Nicotiana.

Investigating pollinator visitation among different species of Zaluzianskya. [SOURCE]

I am sure many more examples exist out there but alas, I only have so much time to pursue my random curiosities these days. Nonetheless, what started as a fun observation in the garden turned into an entertaining dive into ideas that I had not given too much thought to before. What seems like a funny quirk of anatomy turns out to have massive implications for where plants are able to grow and how they are able to reproduce and all of these factors and more have shaped flowering plant evolution over time. Not bad for a few hours in the garden.

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

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

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]

Buzzing Bees Make Evening Primrose Flowers Sweeter

Photo by Guy Haimovitch licensed under CC BY-ND 2.0.

Plants, like all living organisms, must be able to sense and respond to their environment. The more we look at these sessile organisms, the more we realize that plants are far from static in their day to day lives. Recent evidence even suggests that some plants may be able to “hear” their pollinators and react accordingly.

I place the word “hear” in quotes because I want to make sure that we are not talking about hearing in an animalistic sense. Plants do not have ears, a nervous system, or anything like a central processing unit to make sense of such stimuli. What they do have are mechanoreceptors that can sense vibrations and those are what are likely at work in this example.

The beach evening primrose (Oenothera drummondii) is native to southeastern North America. It is pollinated by bees during the day and by moths at night. Like most members of its genus, O. drummondii produces relatively large, showy flowers. That doesn’t mean it steals all of the attention though. Competition for pollinators can be stiff among flowering plants. To sweeten the deal a bit, O. drummondii also produces a fair amount of nectar.

Nectar is costly for plants to produce and maintain. Not only does it take water and carbohydrates away from the rest of the plant, it also puts the reproductive structures at risk of degradation by microbes feeding on sugars as well as nectar thieves who end up drinking the nectar without pollinating the flower. It stands to reason that a plant that can modulate the quality of its nectar reward in response to pollinator availability could potentially increase its fitness. If the plant doesn’t always have to present sugar-rich nectar then why bother? It appears that selective nectar production is exactly the strategy O. drummondii employs.

Photo by Yu-Ju Chang licensed under CC BY-ND 2.0.

Researchers have discovered that individual O. drummondii flowers can rapidly increase the sugar content of their nectar after being exposed to the sound of a visiting bee. Within 3 minutes of being exposed to playbacks of bee wings, the flowers of O. dummondii increased the sugar content of their nectar by 20%. What’s more, flowers that had sensed the vibrations and increased their sugar content were more likely to be visited by bees. This is because bees are really good at sensing the sugar content of nectar.

This is pretty remarkable. Not only does this enable the plant to respond to the availability of pollinators and reduce the chances of nectar spoilage and theft, it significantly increases their chances of pollination. The fact that the response is so rapid (~3 mins) likely stems from the foraging habits of bees, who prefer to limit the amount of time between floral visits. Thus, the faster the plant can respond, the more likely that bees are willing to stick around and visit more flowers.

In terms of a mechanism, researchers believe the flower itself is the main sensory organ involved in the response. As mentioned, plants do produce mechanoreceptor proteins, which can sense physical vibrations. The presence of these proteins within the petals likely plays a role in sensing bee vibrations. Moreover, the bowl-shape of the flower itself may be under some selective pressures that favor the ability of the flower to sense its pollinators. More work is needed to better understand exactly how the signal pathways play out. Also, the question remains as to how wide spread this phenomenon is and how it differs between different plants and floral shapes.

Photo Credits: [1] [2]

Further Reading: [1]

A Rare Case of Ant Pollination in Australia

Photo by Nicola Delnevo [SOURCE]

Ants have struck up a lot of interesting and important relationships with plants. They disperse seeds, protect plants from herbivores and disease, and can even help acquire nutrients. For all of the beneficial ways in which ants and plants interact, pollination rarely enters into the equation. More often than not, ants are actually detrimental to the sex lives of flowering plants. Such is not the case for a rare species of protea endemic to Western Australia called the smokebush (Conospermum undulatum).

The reason ants usually suck at pollination is thanks to a tiny organ called the metapleural gland. For many ant species, this gland secretes special antimicrobial fluids that the ants use to groom themselves. Because ants tend to live in high densities in close quarters, this antimicrobial fluid helps keep their little bodies clean of any pathogens that might threaten their existence. For as good as these fluids are for ants, they destroy pollen grains, rendering them useless for pollination.

Leioproctus conospermi. Photo by Sarah McCaffrey licensed under CC BY-ND 2.0.

As is so often the case in nature, there are always exceptions to the rule and it seems that one such exception is playing out in Western Australia. While investigating the reproductive ecology of the smokebush, researchers noted that ants were regular visitors to their small flowers. They knew that in drier climates, some ant species have evolved to produce considerably less antimicrobial fluids. The thought is that drier climates tend to harbor fewer microbial pathogens and thus ants don’t need to waste as much energy protecting themselves from such threats. If this was the case in Western Australia then it was entirely possible that ants could potentially serve as pollinators for this plant. Armed with this hypothesis, they decided to take a closer look.

It turns out that the floral morphology of the smokebush lends well to visiting ant anatomy. The tiny flowers produce a small amount of nectar at the base. As ants shove their heads down into the flower to get a drink, it triggers an explosive mechanism that causes the style the smack down onto the back of the ant. In doing so, it also mops up any pollen the ant may be carrying. At the same time, the anthers explosively dehisce, coating the visitor with a fresh dusting of pollen. During their observations, researchers noted that ants weren’t the only insects visiting smokebush blooms. They also noted lots of visitation from invasive honeybees (Apis mellifera) and a tiny native bee called Leioproctus conospermi.

(A) White flowers of Conospermum undulatum. (B) Floral details. (C–H) Insects visiting flowers of C. undulatum: (C) Leioproctus conospermi; (D) Camponotus molossus; (E) Camponotus terebrans; (F) Iridomyrmex purpureus; (G) Myrmecia infima; (H) Apis mellifera. [SOURCE]

After recording visits, researchers needed to know whether any of these floral visitors resulted in successful pollination. After all, just because something visits a flower doesn’t mean it has what it takes to get the job done for the plant. By looking at differences in seed set between ant and bee visitors, they were able to paint a fascinating picture of the pollination ecology of the rare smokebush.

It turns out that ants are indeed excellent pollinators of this shrub, contributing just as much to overall seed set as the tiny native Leioproctus conospermi. Alternatively, invasive honeybees barely functioned as pollinators at all. Their heads were too big to effectively trigger the pollination mechanism of the flowers but nonetheless were able to access the nectar within. As such, honeybees are considered nectar thieves for the smokebush, harming its overall reproductive effort rather than helping.

Amazingly, the effectiveness of ants as smokebush pollinators is not because they produce less antimicrobial fluids. In fact, these ants were fully capable of producing ample amounts of these pollen-killing substances. Instead, it appears that the plant itself has evolved to tolerate ant visitors. Smokebush pollen is resistant to the toxic effects of the metaplural gland fluids. With plenty of hungry ants always on the lookout for food, the smokebush has managed to tap in to an abundant and reliable vector for pollination. No doubt other examples exist, we simply have to go looking.

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

Further Reading: [1]

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]

The Heartleaf Twayblade Orchid

Photo by Cptcv licensed under CC BY-ND 2.0.

The heartleaf twayblade is truly a sight for sore eyes.... that is, if you can find it. This diminutive orchid stands no more than 30 cm tall when in bloom and, for much of its life, exists as a single pair of tiny, heart-shaped leaves. Finding this species in bloom has been one of the major highlights of the last few years of botanizing. Getting to see it up close makes me wonder how many times I may have passed it over completely.

A closeup examination of the flowers will reveal what looks like tiny little humanoids. Indeed, the flowers are complex little structures. Tiny trigger hairs located at the base of the pollinia squirt glue on the back of visiting insects, which affixes the pollen sacs or pollinia. One to two days after the pollinia have been removed the stigmas become receptive to pollen. Though this orchid can self fertilize, differential ripening of sexual parts like this helps ensure cross pollination between different individuals.

With flowers so small, it is a wonder that insects can even find them. As it turns out, the flowers emit a foul smelling odor, though one would be hard pressed to detect it having to bend down so close to the forest floor. This attracts a wide variety of small insects like wasps and flies. The most common visitors, however, are fungus gnats. Ever abundant in the moist duff of the forest, these tiny dipterids offer plenty of opportunity for pollination. The orchid even sweetens the deal a bit by producing a small amount of nectar.

Being so small it is quite easy to overlook this plant. One must put in a bit of searching to find them. Their tiny size also means that they are often under-represented in conservation efforts as well. Entire populations can exist in only a few square meters of forest and thus are quite sensitive to disturbance. Timber harvesting and sprawl represent the largest threats the this species but luckily it has a surprisingly large geographic distribution. Still, keep an eye out for this lovely little species. They may be hard to find but they are well worth the effort!

Photo Credit: [1]

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

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]

North America's Climbing Fern

There are few things on a hike that get me pumped more than hearing someone call out "Hey, I found something weird over here!" It's even more exciting when that person knows what they are talking about. Sometimes that "something" is a familiar species in a strange spot, or growing in a strange way. Sometimes, however, it is something new and exciting that you have been wanting to encounter for years.

This is how I finally met the American climbing fern (Lygodium palmatum). Tangled among the branches of a shrub was indeed a strange site. The tiny, palmate pinnules are not a dead giveaway as to its true identity. Regardless of looks, this is in fact a fern. It is the only member of this genus native to North America. Its cousins, the Japanese climbing fern (Lygodium japonicum) and the Old World climbing fern (Lygodium microphyllum) can also be found on this continent but they have become very invasive in the southeast.

I know what some of you may be thinking, "if this is a fern then where are the fronds?" This was my first thought as well. My first guess was aimed at each palmate leaf. Wrong. The correct answer is the whole vine! Each climbing vine of this fern is a single frond. The palmate leaves are actually the pinnules. The stem, or rachis as it is called in ferns, twines around branches and stems in a vine-like fashion, unfurling pinnules as it goes. What is most impressive is that these fronds can grow as long as 15 feet. Quite impressive by North American fern standards. Fertile pinnules form at the ends of these fronds. Their lacy appearance is quite beautiful juxtaposed with the hand-like, sterile pinnules.

The American climbing fern can be found growing throughout eastern North America. It is a fern of wet places, enjoying acidic soils and bright sunlight. Unfortunately its preference for wetlands has landed it on threatened and endangered lists throughout its range. Our nasty habit of draining, farming, and developing wetlands means that the American climbing fern (as well as many of the other species it shares its habitat with) is losing habitat at an alarming rate.

Further Reading:
http://plants.usda.gov/core/profile?symbol=LYPA3

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]