Not All Pitchers Are Equal: How Prey Capture Has Driven Speciation in the genus Nepenthes

Species of the genus Nepenthes are as bizarre as they are beautiful. Known the world around for their carnivorous lifestyle, these plants looks like something out of a macabre art exhibit. It is easy to get caught up in this beauty. I often find myself lost in thought while staring at full grown specimen. How did this genus come to be? Why are they so diverse? What is going on with the morphology of these plants?

Nepenthes hail from nutrient poor habitats, which has driven them to supplement their growth with nutrients gained via the breakdown of a variety of organisms. The business ends of a Nepenthes are their pitchers. We get so caught up in the bewildering diversity of shapes, colors, and sizes that we often overlook them as the anatomical marvels of evolution that they truly are. Whereas the main body of these plants often look quite similar among different species, it's the pitchers that really allow us to separate them out as distinct species. Pitcher morphology not only gives us a convenient means to identify these plants, research is now showing that the structure of these pitchers is likely to be the driving force in their evolution. 

Let's back up for a second. Before we get to the subject of adaptive radiation, we should take a closer look at the anatomy of these plants. To put it simply, the pitchers of Nepenthes are actually leaves, albeit highly modified versions. What we readily recognize as the photosynthetic leaves of a Nepenthes plant are actually modified leaf bases or petioles. Over evolutionary time, these bases have flattened to increase the amount of surface area available for photosynthesis.

From the tip of each of these "leaves" is produced a tendril. Gradually this tendril will elongate and the tip starts to swell. This tip will eventually become the pitcher. The pitchers themselves are highly modified leaves. They are some of the most specialized leaves in all of the plant kingdom. As the tip grows larger, it becomes clear that there is a distinctive lid apparatus. Once the pitcher is fully mature, this lid pops open revealing the death trap filled with digestive fluids.

As if producing pitchers wasn't cool enough, each species of Nepenthes produces two distinct forms - lower pitchers, which are produced by young plants as well as on mature plants near the ground, and upper pitchers, which are produced up on the climbing stems as they vine through the canopy. The upper and lower pitchers look radically different from one another to the point that one may easily confuse them for different species. The reason for such stark differences has to do with the type of prey captured. Lower pitchers are generally larger and can capture prey that crawls along the forest floor. Upper pitchers tend to be more slender and most often capture flying insects as well as other creepy crawlies hanging out in the forest canopy.

The key to the success of these traps seems pretty straight forward - insects attracted by bright colors and sweet nectar land on the traps and fall to their death. Certainly this holds true throughout the genus, however, there are at least two major variations on this theme and a handful of bizarre mishmashes. As the lid of a Nepenthes pitcher starts to open, a ring of tissue called the peristome unfurls. The shape and color varies wildly between species and this has to do with the methods in which they capture their prey. These variations are the key to the amazing diversity of Nepenthes we see throughout the range of this genus.

Nepenthes vogelii

Nepenthes vogelii

The first of the three strategies is referred to as the 'insect aquaplaning' strategy. Insects walking around on the peristome of the pitcher find it hard to get a foothold. These are species such as N. raja, N. ampullaria, and N. bicalcarata (just to name a few). The slipperiness of the peristome of these species is further enhanced when humidity is high. Considering how much it rains in these habitats, it is no wonder why capture efficiency is often as high as 80%. Although there is some variation on this theme, pitchers that utilize the insect aquaplaning strategy often lack waxy cells on the interior of the pitcher walls.

Slippery pitcher walls are the second strategy that Nepenthes have converged upon. These are species such as N. diatas, N. mirabilis, and N. alata (again, just to name a few) Insects attracted to the pitchers are often lured in by sweet nectar. Once they cross the lip of the pitcher, prey find it hard to hang on and inevitably fall inside. Once this happens, waxy cells lining the interior walls make it impossible for anything to climb back out. It should be mentioned that a slippery peristome and waxy pitcher walls are not mutually exclusive. That being said, there are clear trends among species that show a reduction in waxy cells as peristome size and slope increases.

This brings us to the oddballs. There are species like N. lowii, whose pitchers function as a toilet bowl for shrews, and N. aristolochioides, whose pitchers seemed to have abandonded both strategies and now function as light traps similar to what we see in Darlingtonia. Regardless of their strategy, the diversity in trapping mechanisms appear to be the driving force behind the bewildering diversity of Nepenthes

Nepenthes aristolochioides

Nepenthes aristolochioides

All of the evidence taken together shows that prey capture is at the core of this radiation. There seems to be incredibly strong selective pressures that result in strong divergence in pitcher morphology. The disruptive selection that seems to be driving a wedge between the insect aquaplaning strategy and the waxy wall strategy may have its roots in reducing competition. Nutrients are low and competition for food is high. Different Nepenthes species could be evolving to capture different kinds of prey. Even closely related species such as N. ampullaria, N. rafflesiana, N. mirabilis, N. albomarginata, and N. gracilis all seem to occupy their own unique spot on the spectrum of prey capture strategy.

It could also be that Nepenthes are responding to the specific characteristics of the habitats in which they are found. Those inhabiting drier sites may favor the waxy wall strategy whereas those living in wetter habitats tend to favor the slippery peristome. More work needs to be done to investigate where and how these different strategies are maximized. Until then, I think it is safe to say that the diversity of this incredible genus has a lot to do with obtaining food. 

Photo Credits: [1] 

Further Reading:

[1] [2] [3]

 

On Soil and Speciation

Lord Howe Island

Many of you will undoubtedly be familiar with some variation of this evolutionary story: A population of one species becomes geographically isolated from another population of the same species. Over time, these two separate populations gradually evolve in response to environmental pressures in their respective habitats. After enough time has elapsed, gradual genetic changes result in reproductive isolation and eventually the formation of two new species. This is called allopatric speciation and countless examples of this exist in the real world.

At the opposite end of this speciation spectrum is sympatric speciation. Under this scenario, physical isolation does not occur. Instead, through some other form of isolation, perhaps reproductive or phenological, a species gives rise to two new species despite still having contact. Examples of this in nature are far less common but various investigations have shown it is indeed possible. Despite its rarity, examples of sympatric speciation have nonetheless been found and one incredible example has occurred on a small oceanic island off the coast of Australia called Lord Howe Island.

Howea belmoreana and Howea forsteriana

Lord Howe Island is relatively small, volcanic island that formed approximately 6.4–6.9 million years ago. It is home to four distinct species of palm trees from three different genera, all of which are endemic. Of these four different palms, two species, Howea belmoreana and Howea forsteriana, are quite common. Interestingly enough, H. forsteriana, commonly known as the kentia palm, is one of the most commonly grown houseplants in the entire world. However, their horticultural value is not the most interesting thing about these palms. What is most remarkable is how these two species arose. 

Multiple genetic analyses have reveled that both species originated on Lord Howe Island. This is kind of odd considering how small the island actually is. Both palms can regularly be found growing in the vicinity of one another so the big question here is what exactly drove the evolution of their common ancestor? How does a single species growing on a small, isolated island become two? The answer is quite surprising.

Howea belmoreana

When researchers took a closer look at the natural histories of these two species, they found that they were in a sense isolated from one another. The isolation is due to major phenological or timing differences in their reproductive efforts. H. forsteriana flowers roughly six weeks before H. belmoreana. Flowering time is certainly enough to drive a wedge between populations but the question that still needed answering was how do such phenological asynchronies occur, especially on an island with a land area less than 12 square kilometers? 

As it turns out, the answer all comes down to soil. Individuals of H. belmoreana are restricted to growing in neutral to acidic soils whereas H. forsteriana seems to prefer to grow in soils rich in calcarenite. These soils have a more basic pH and dominate the low lying areas of the island. Growing in calcarenite soils is stressful as they are poor in nutrients. This physiological stress has caused a shift in the way in which the flowers of H. forsteriana mature. When found growing on richer volcanic soils, the researchers noted that the flowers mature in a way that is more synchronous, not unlike the flowers of H. belmoreana.

Thanks to their attention to detailed life history events and conditions, researchers were able to show that soil preferences caused a phenological shift in the flowering of these two related species. Because they flower at completely different times when growing on their respective soil types, enough reproductive isolation was introduced to disrupt the random mating process of these wind pollinated palms. As soon as such reproductive biases are introduced, speciation can and will occur.

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

Further Reading: [1]

The Power of Leaves

When we think of the dominance of flowering plants on the landscape, we usually invoke the evolution of flowers and seed characteristics like endosperm and fruit. However, evolutionary adaptations in the structure of the angiosperm leaf may have been one of the most critical factors in the massive diversification that elevated them to their dominant position on the landscape today. 

Leaves are the primary organs used in water and gas exchange. They are the centers of photosynthesis, allowing plants to take energy from our closest star and turn it into food. To optimize this system, plants must balance water loss with transpiration in order to maximize their energy gain. This requires a complex plumbing system that can deliver water where it needs to be. It makes sense that plant physiology should maximize vein production, however, there are tradeoffs in doing so. Veins are not only costly to construct, they also displace valuable photosynthetic machinery. 

It appears that this is something that flowering plants do quite well. Because leaves fossilize with magnificent detail, researchers are able to look back in time through 400 million years of leaf evolution. What they found is quite incredible. There appears to be a consistent pattern in the vein densities between flowering and non-flowering plants. The densities found in angiosperm leaves both past and present are orders of magnitude higher than all non-flowering plants. These high densities are unique to flowering plants alone. 

This innovation in leaf physiology allowed flowering plants to maintain transpiration and carbon assimilation rates that are three and four times higher than those of non-flowering plants. This gives them a competitive edge across a multitude of different environments. The evolution of such dense vein structure also had major ramifications on the environment. 

The massive change in transpiration rates among the angiosperm lineage is likely to have completely changed the way water moved through the environment. These effects would be most extreme in tropical regions. Today, transpiration from tropical forests account for 30-50% of precipitation. A lot of this has to do with patterns in the intertropical convergence zone, which ensures that such humid conditions can be maintained. However, in areas outside of this zone such as in the Amazon, a high abundance of flowering plants with their increased rates of transpiration enhances the amount of rainfall and thus forms a sort of positive feedback.

Because precipitation is the single greatest factor in maintaining plant diversity in these regions, increases in rainfall due to angiosperm transpiration effectively helps to maintain such diversity. As angiosperms rose to dominance, this effect would have propagated throughout the ecosystems of the world. Plants really are the ultimate ecosystem engineers. 

Photo Credit: Bourassamr (Wikimedia Commons)

Further Reading: [1]

Mighty Magnolias

Magnolias are one of those trees that even the non-botanically minded among us will easily recognize. They are one of the more popular plant groups grown as ornamentals and their symbolism throughout human history is quite interesting. But, for all this attention, few may realize how special magnolias really are. Did you know they they are one of the most ancient flowering plant lineages in existence?

Magnolias first came on to the scene somewhere around 95 million years ago. Although they are not representative of what the earliest flowering plants may have looked like, they do offer us some interesting insights into the evolution of flowers. To start with, the flower bud is enclosed in bracts (modified leaves) instead of more differentiated sepals. The "petals" themselves are not actually petals but tepals, which are also undifferentiated. The most striking aspect of magnolia flower morphology is in the actual reproductive structures themselves.

Magnolias evolved before there were bees. Because of this, the basic structure that makes them unique was in place long before bees could work as a selective pressure in pollination. Beetles are the real pollinators of magnolia flowers. The flowers have a hardened carpel to avoid damage by their gnawing mandibles as the feed. The beetles are after the protein-rich pollen. Because the beetles are interesting in pollen and pollen alone, the flowers mature in a way that ensures cross pollination. The male parts mature first and offer said pollen. The female parts of the flower are second to mature. They produce no reward for the beetles but are instead believed to mimic the male parts, ensuring that the beetles will spend some time exploring and thus effectively pollinating the flowers.

It is pretty neat to think that you don't necessarily have to track down a dawn redwood or a gingko to see a plant that has survived major extinction events. You can find magnolias very close to home with a keen eye. Looking at one, knowing that this is a piece of biology that has worked for millennia, is quite astounding in my opinion.

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

The World's Only (Known) Photosynthetic Vertebrate

You may be asking yourself right now why I have posted a picture of a salamander this morning. This is a plant blog after all! Well, what I am about to tell you may seem a bit crazy, but I assure you this discovery has opened up some doors that science never really considered a possibility before. The yellow spotted salamander (Ambystoma maculatum) is the first and only (known) photosynthetic vertebrate ever discovered!

That's right. You heard me. A photosynthetic animal. More accurately speaking, it is the embryos of this species that undergo photosynthesis. To understand why this happens we must back up a little bit. Yellow spotted salamanders are a species of mole salamander that can be found in wet areas of eastern North America. They spend most of their adult lives underground, hiding beneath logs and rocks in the forest, feeding on any manner of invertebrates. Once a year (around this time) adult yellow spotted salamanders undertake a massive migration down to the pools where they mate. On the first few warm, rainy nights, thousands of salamanders can be seen trucking their way to vernal pools and ponds to breed. It is an amazing sight to behold.

The thing about yellow spotted salamanders is they will only breed in fishless ponds. Their larvae would be an easy meal for many predatory fish species. The problem that arises out of this breeding strategy is that fishless ponds tend to be very low in oxygen. It has long been known that the eggs of this species form a symbiotic relationship with an algae. The algae produce oxygen for the developing embryo and the embryo feeds the algae via its nitrogen rich waste and CO2. This relationship was always thought to be external, that is until Ryan Kerney of Dalhousie University in Halifax, Nova Scotia discovered that embryos of a certain age actually had algae living within their cells.

They algae don't seem to start off inside the cells though. This may be why this relationship wasn't discovered earlier. Roger Hangarter at Indiana University found that it isn't until parts of the salamander's nervous system begin to develop that the algae move into the embryo and set up shop. The algae then reside near the salamander's mitochondria, which are the powerhouses of the cell. So where are the algae coming from? While more research needs to be done, Karney also discovered the presence of algae in the oviducts of adult female spotted salamanders. It is looking like mother salamanders are actually passing the algae on to their offspring. 

Though this is the first and only instance we know of this sort of photosynthetic relationship in vertebrate animals, this discovery has opened the door for exploring the possibility of other photosynthetic symbionts. It has also allowed scientists a different avenue to explore just how cells recognize and deal with foreign bodies. We live in such an amazing world!

Further Reading: [1] [2] [3]

 

Seed Anchor

Epiphytic plants live out their entire lives on the trunks or branches of trees. Using their roots, they attach themselves tightly to the bark. Spend any amount of time in the tropics and it will become quite clear that such a lifestyle has been very successful for a plethora of different plant families. Still, living on a tree isn't easy. Epiphytic plants must overcome harsh conditions among or near the canopy.

One of the biggest challenges these plants face starts before they even germinate. This is especially true for orchids. Orchid seeds are more like spores than they are seeds. They are so small that thousands could fit inside of a thimble. Upon ripening, the dust-like seeds waft away on the slightest breeze. In order for epiphytic species to germinate and grow, their seeds must somehow anchor themselves in place on a trunk or branch. Inevitably most seeds are doomed to fail. They simply will not land in a suitable location. It stands to reason then that any adaptation that increases their chances of finding the right kind of habitat will be favored. That's where the strange coils on the tip of Chiloschista seeds, a genus of leafless orchids native to southeast Asia, New Guinea, and Australia, come in. For these orchids, this process is aided by some truly unique seed morphology.

Unlike most orchid seeds that are nothing more than a thin sheath surrounding a tiny embryo, the seeds of Chiloschista have additional parts. These "appendages," which are specialized seed coat cells, are tightly wound into coils. Upon contact with water, these coils shoot out like tiny grappling hooks that grab on to moss and bark alike. In doing so, they anchor the seed in place. By securing their hold on the trunk or branch of a tree, the seeds are much more likely to germinate and grow. This is one of the most extreme examples of seed specialization in the orchid family.

Photo Credit: [1] [2]

Further Reading: [1]

Pollination with a Twist

Ensuring that pollen from one flower makes it to another flower of that species is paramount to sexual reproduction in plants. It's one of the main drivers of the diversity in shapes, sizes, and colors we see in flowers across the globe. Sometimes the mechanism isn't so obvious. Take, for instance, the flowers of Impatiens frithii.

The flowers of this Cameroonian endemic have been a bit of a puzzle since its discovery. Like all Impatiens, they have a long nectar spur. However, the spur on I. frithii is uniquely curved. This puzzled botanists because most of the Impatiens in this region are pollinated by sunbirds. The curved spur would appear to make accessing the nectar within quite difficult for a bird. Still, just because we can't imagine it, doesn't mean that it's impossible. Something must pollinate this lovely little epiphyte in one way or another. This is where close observation comes in handy.

Thanks to remote cameras and lots of patience, botanists were able to record pollination events. They quickly realized that sunbirds are indeed the primary pollinator of this species. This was a bit of a surprise given the shape of the flower. However, the way in which the flowers deposit pollen on this birds is what is most remarkable. As it turns out, successful reproduction in I. frithii all comes down to that curved nectar spur. 

When a sunbird probes the flower for nectar, its beak follows the contour of the spur and this causes the entire flower to twist. As it twists, the anthers and stigma make contact with the chin of the bird. This is unlike other Impatiens which deposit the pollen on top of the heads of visiting birds.

Such an adaptation is quite remarkable in many ways. For one, it is elegantly simple. Such a small alteration of floral architecture is all that is required. Second, by placing pollen on the underside of the head, the plant guarantees that only pollen from its species will ever come into contact with the stigma. This is what we call reproductive isolation, which is an important driver in speciation.

Photo Credit: [1]

Further Reading: [1]

Convergent Carnivores

A carnivorous lifestyle has evolved independently in numerous plant lineages. Despite the similarities between genera like Nepenthes, Sarracenia, and Cepholotus they are not closely related. Researchers have wondered how the highly modified leaves of various carnivorous plant species evolved into the insect trapping and digesting organs that we see today. Thanks to a recent article published in Nature, it has been revealed that the mechanisms responsible for carnivory in plants are a case of convergent evolution.

This research all started with the Australian pitcher plant Cepholotus follicularis. More closely related to wood sorrels (Oxalis spp.) than either of the other two pitcher plant families, this species offers a unique window into the genetic controls on pitcher development. Cepholotus produces two different kinds of leaves - normal, photosynthetic leaves and the deadly pitcher leaves that have made it famous the world over.

By observing which genes are activated during the development of these different types of leaves, the research team was able to identify which alleles have been modified. In doing so, they were able to identify genes involved in producing the nectar that attracts their insect prey as well as the genes involved in producing the slippery waxy coating that keeps trapped insects from escaping. But they also found something even more interesting.

Next, the team took a closer look at the digestive fluids produced by Cepholotus as well as many other unrelated carnivorous plant species from around the world. In doing so, the team made a startling discovery. They found that the genes involved in synthesizing the deadly digestive cocktails among these disparate lineages have a similar evolutionary origin.

Although they are unrelated, the ability to digest insects seems to have its origins in defending plants against fungi. You have probably heard someone say that fungi are more similar to animals than they are plants. Well, the polymer that makes up the cell walls of fungi is the same polymer that makes up the exoskeleton of insects - chitin. By comparing the carnivorous plant genes to those of the model plant Arabidopsis, the team found that similar genes became active when plants were exposed to fungal pathogens.

It appears that carnivorous plants around the world have all converged on a system in which genes used to defend themselves against fungal infection have been co-opted to digest insect bodies. Taken together, these results show that the path to carnivory in plants is surprisingly narrow. Evolution doesn't always require the appearance of new alleles but rather a retooling of genes that are already in place. 

Photo Credits: [1] [2]

Further Reading: [1]

 

 

Captive Pollinators

In order to ensure pollination, leafflower trees in the genus Glochidion have entered into an intimate relationship with a small family of moths. Their flowers have become so specialized that no other insect is capable of pollinating them. In return, female moths are provided with an edible place to lay their eggs - the fruit of the tree. One species of leafflower has taken this relationship to the extreme. It holds its pollinators captive. In order to understand this bizarre relationship, we must first take a closer look at this interesting pollination syndrome.

Ecologists refer to this type of pollination syndrome as "brood pollination." In the case of the leafflower trees, pollination is achieved thanks to female moths known commonly as leafflower moths. Gravid female leafflower moths locate the blooms thanks to a special perfume tailored specifically for each species. The females first visit the male flowers where they pick up some pollen. Next they visit the female flowers where they will then deposit the pollen into a special chamber that can only be accessed by the female moths' proboscis.

After pollination, the female leafflower moth will then locate the ovaries of the flower and using a needle-like ovipositor, will deposit eggs within the undeveloped fruits. The larvae within eventually hatch right next to their food source - leafflower seeds. The larvae aren't gluttons. They will only eat one or two of the dozens of seeds developing within the fruit. Although this may seem wasteful on the part of the plant, it makes a lot of sense from an evolutionary perspective. Essentially it reduces the likelihood that the moths will try to cheat the system. Glutenous larvae that eat more than one or two seeds will be penalized in the long run because fewer host plants will be available. By tying the reproductive abilities of the moth to the production of fruit, the tree ensures regular pollination.

For most of the leafflower/moth pairs, once the seed meal is over, the larvae chew out of the fruit and fall to the ground to pupate. However, this is not the case for a leafflower known scientifically as Glochidion lanceolarium. It takes this relationship a step further by holding the larvae captive for nearly a year.

Cut open an fruit of this leafflower and there is a chance you might find a fully formed moth waiting patiently inside one of the swollen chambers. Instead of chewing out before it pupates, the moth is held captive within. Only when the fruits mature and split open will the moths be released. This happens just as the new crop of flowers is opening. The tree is literally controlling when its obligate pollinator is available to do its reproductive bidding.

The uniquely intimate nature of this relationship goes beyond simply being interesting. By studying how these two partners interact in relation to the other leafflower/moth partners around the Old World tropics researchers are gaining a better understanding of how such mutualisms evolve.

Photo Credits: [1] [2]

Further Reading: [1]

A Unique Passionflower Endemic to Costa Rica

I love small flowers, especially if they pack in a lot of detail. That's is why this passion flower caught my eye. Meet Passiflora boenderi, a charismatic vine endemic to a small region of Costa Rica. Apparently this species had been sitting around in herbaria for years under a different name. It wasn't until living specimens were observed that botanists realized it is a distinct species.

There is a lot to look at on this species. The flowers themselves are some of the smallest in the genus. They pack in all of the detail of a larger passion flower, just in miniature. The leaves are quite stunning as well. They're bilobed with a tinge of purple and covered in bright, orange-yellow spots. The spots themselves serve an important role in protecting this plant from herbivores.

The genus Passiflora is part of an intense evolutionary arms race with a genus of butterfly known as Heliconius. Their caterpillars feed on the foliage of passion flowers. As such, Passiflora have evolved a variety of means that help them to avoid the attention of gravid female butterflies. The orange spots on the leaves of P. boenderi are one such adaptation and they serve a dual function.

The first is a visual deterrent. Female Heliconius prefer to lay their eggs on caterpillar-free leaves. This makes sense. Why bother laying eggs where there will be ample competition for food. The spots mimic, both in size and shape, the appearance of Heliconius eggs. A female looking for a spot to lay will see these spots and move on to another plant. In addition to the visual mimicry, these spots also secrete nectar. The energy-rich nectar inevitably attracts ants, which viciously defend them as a food source. If a caterpillar (or any other herbivore fore that matter) were to start munching on the leaves, the ants quickly drive them off.

Because of its limited range, P. boebderi is under threat of extinction. Habitat destruction of its lowland habitat for palm oil, pineapples, and vacation resorts is an ongoing threat to the long term survival of this species and many others. I was fortunate enough to have encountered this plant growing in the Cliamtron at the Missouri Botanical Garden but I fear that if we keep on doing what we humans are so good at, botanical gardens may be the only place this species will be found growing in the not too distant future.

Further Reading: [1] [2]

A Shrub and Its Buffer Zone

Confession: I can be really bad at recognizing patterns. It's not my strong point. As such, I tend to remain skeptical of what I think I am seeing. Sometimes I am right, though. A recent stroke of luck came while I was hiking through some scrubby habitat in northern Florida. I walked out into a clearing to get a better view of a pond when I saw some interesting shrubs up on the banks. The area was largely covered in tufts of warm season grasses but the shrubs seemed to be ringed by barren, white sand. My botanist friend was kind enough to point out that the shrubs I was looking at were none other than sandhill rosemary (Ceratiola ericoides). With a name attached to these species, I could dive into the literature on this plant to see if I was actually seeing a true pattern or not.

Before we get to the meat of the article, it would be nice to first introduce you to the sandhill rosemary. C. ericoides is not a true rosemary at all. Its resemblance to the culinary mint is purely superficial. C. ericoides is a heath (family Ericaceae) and is the only member of its genus. It can be found growing in dry, scrubby habitats throughout southeastern North America. It is dioecious meaning each shrub is either male or female. Unlike its showier cousins, this heath is not pollinated by insects. Instead, it relies on wind. Because of this, C. ericoides flowers are highly reduced structures produced in the axils of leaves near the tips of its branches.

The scrubby habitats it calls home are challenging places for plants to live. The sandy soils drain water rapidly and are prone to shifting with the winds. The stout, needle like leaves are a fantastic adaptation for minimizing water loss during the hottest, driest months of the year. Also, regular fires are the norm. Burning is vital to the health of this region, however, C. ericoides does not seem to be very well adapted to cope with it. Instead, these shrubs are killed by fire, relying on the seed bank for regeneration. But that isn't the only thing this species has evolved in order to cope with a regular fire regime. As it turns out, C. ericoides may be utilizing chemical warfare to increase its chances of survival.

C. ericoides is what we call "allelopathic." Allelopathy can be defined as "the direct or indirect harmful or stimulatory effect of one plant on another through the production and release of chemical compounds" and is "an important form of plant-to-plant interference in natural and agricultural settings" (Rice 1984). In other words, allelopathic plants utilize chemicals that are toxic to other plants in order to gain an upper hand when it comes to acquiring space to grow. For C. ericoides, this may also mean keeping itself safe from fire.

As anyone who has tried to light a fire knows, a little fuel goes a long way. In the wild, plant materials make up the fuel load. The more plant material lying around, the more fuel the fire has to burn through. Much of the understory of these habitats are filled with fire adapted plant species. Grasses are possibly the most fire tolerant of them all. What's more, grasses often release specialized compounds when they burn that actually increase the temperature of the fire. This is often bad news for less fire adapted plants in the vicinity. If grasses and other fire adapted species were to be growing near C. ericoides, they would not only increase the chances of fire reaching the shrub but also increase the intensity of the flames. This is where the allelopathy comes in.

Evidence from greenhouse experiments has shown that the allelopathic compounds from C. ericoides inhibit the germination and growth of other plant species. This is especially true for fire adapted grasses. Although these chemicals are abundant in the leaves of C. ericoides, research also shows that they are produced in the roots as well. As the leaves fall off, they decompose and release their chemical cocktails into the soil immediately surrounding the shrub. This keeps plants at bay in the immediate vicinity while the roots go a bit further. Since the roots of C. ericoides branch outwards from the plant, the effectiveness of its chemical warfare is increased by a few meters radius around the shrub. Indeed, it is believed that C. ericoides is actually keeping the surrounding area clear of most fire adapted vegetation. In doing so, the shrubs are creating a fire-free buffer zone.

Although more work needs to be done in order to understand the degree to which these effects occur in the wild, this is nonetheless tantalizing evidence that such plant interactions are shaping the landscape in ways we don't fully understand. On a personal note, it was exciting to know that there really was something to the barren ring patterns I observed around each shrub.

Further Reading: [1] [2] [3]
 

Floral Deterrent

There is no mistaking the allure of certain floral scents. Entire industries have developed around capturing the essence of plant reproduction. Millions of years before we humans adopted floral scents for our own bidding, plants were producing them to attract pollinators. Even plants that produce sickening smells meant to mimic rotting flesh are trying to get the attention of something. It seems so obvious that these perfumes evolved as attractants but there are some plant species whose floral scents do the opposite. 

When I first caught a whiff of the blooms of the fragrant olive (Osmanthus fragrans) it didn't take long to track down its source. In my opinion it is one of the most enticing fragrances I have ever encountered. Native throughout much of Asia, this evergreen shrub produces sprays of tiny, pale, 4 lobed blossoms. Its attractive form and heavenly scent have led to its popularity in horticultural circles the world over. Surely its intense fragrance also makes it quite popular with pollinators. The truth is actually quite surprising.

In its native range, few insects seem to show it any attention. Aside from some hover flies, the list of floral visitors is surprisingly quite depauperate. What is going on? Why would this shrub go through the trouble of producing such volatile compounds? Has its intended pollinator gone extinct? Though it can be difficult to answer such inquiries, research done in Japan suggests that these scents may actually function as a deterrent rather than a lure. 

Researchers looked at a common butterfly species known to pollinate other flowering species in the area. The results of their experiments were quite shocking to say the least. Even when food was withheld for a period of time, the butterflies never visited the flowers of the fragrant olive. Only when the team replaced the flowers with replicas infused with a neutral scent did the butterflies pay them any attention. 

The fact that hover flies do in fact visit the flowers suggests that the scent compounds serve a dual function - attracting the intended pollinators while at the same time deterring potential nectar thieves. More work is needed before we can be completely confident in these conclusions but the idea nonetheless highlights the fact that more is going on with flowers than we realize. 

Photo Credit: hto2008 (http://bit.ly/2hPOhnO

Further Reading: [1]

A Primer on Trigger Plants

I would like to introduce you to another group of plants capable of abrupt movements. Whereas many species have evolved moving parts in order to capture prey or deter herbivores, the following genus moves as means of achieving pollination. Meet the genus Stylidium a.k.a. the trigger plants.

Native to parts of Asia and Australia, these beautiful little herbs are quite diverse, making generalizations difficult. Still, there is one thing they all share, a fused set of reproductive organs that lash out at unsuspecting pollinators. When a visiting insects of sufficient size lands on a flower, its weight causes a rapid change in turgor pressure within the column's tissues.

The rapid change in pressure sends the column flying. The position of this reproductive hammer varies from species to species. Some bash their pollinators on the back whereas others strike them under the abdomen. When the flowers first mature, only the male portions are mature. Thus, the initial visit dusts the insect with pollen. Once the pollen is gone, the column resets itself and the female portions start to mature. The next time an insect visits the bloom, the stigma will do the bashing. With any luck, the visiting insect will have already been dusted with pollen from a previous plant. In this way, the plant avoids self pollination.

Another morphological aspect shared among member of this genus is the production of glandular trichomes. These minute hairs cover the body of the plant and produce sticky mucilage that ensnares tiny insects. It was originally thought that this was a merely a defense mechanism that may represent a form of proto-carnivory.

However, analysis of the mucilage revealed that plant is also producing digestive enzymes capable of breaking down insects unfortunate enough to have been caught. It remains to see whether or not the plants absorb nutrients in the same way as sundews but the fact that these plants share the same nutrient-poor habitats as many other Australian carnivores lends some credibility.

Photo Credit: http://bit.ly/2hJjMyc and Francis Nge

Further Reading: [1] [2]

The Ant-Farming Tillandsias

Tillandsias are all the rage. Their relative ease of care has found them included in seemingly every terrarium sold these days; often in very inappropriate circumstances that result in their death. There is no denying that these epiphytic relatives of the pineapple are unique and beautiful plants but I would argue that their ecology is probably the coolest aspect about them. I am particularly fond of the bulbous species because of their relationship with ants.

That's right, there are upwards of 13 species of bulbous Tillandsia that offer up housing for ants. If you look closely at the leaves of these species, you will notice that they roll up to form tubes that lead down into the bulb at the base. The space between the leaves forms a hollow chamber, functioning as a perfect microclimate for ants to nest. In many habitats, these Tillandsia offer better housing than the surrounding environment. One would be surprised at how many ants can fit in there too. Colonies containing anywhere between 100 - 300 ants are not unheard of.

The rewards for the plant are obvious. Ants provide nutrients as well as protection. In return the ants get a relatively safe and dry place to live. Ant domatia have been recorded in roughly 13 different species, many of which are some of the most commonly sold Tillandsias on the market such as T. baileyi, T. balbisiana, T. bulbosa, and T. caput-medusae. If this doesn't make your hanging glass Tillandsia orb even cooler then I don't know what will.

Photo Credits: scott.zona (http://bit.ly/16kZ1RR) and Alex Popovkin (http://bit.ly/1BXMEUH)

Further Reading: [1] [2]

A Cave Dwelling Nettle From China

Caves and plants do not seem like a good combo. Plants need sunlight and caves offer very little to none of it. However, plants in general never seem to read the literature we write about them. As such, they are constantly surprising botanists all over the world. 

A recent example of this was published back in September of 2012. A team of botanists exploring limestone gorges in southwestern China stumbled upon three new members of the nettle family. One of these nettles seemed to be right at home growing well within two limestone caves. 

Needless to say this was quite a shock to the botanists. The regions in which these plants were growing were quite dim, with light levels ranging from a mere 0.04% to a measly 2.78 % of full daylight! Although this is by no means complete darkness, it is an incredibly low amount of sunlight for a plant that still relies on photosynthesis to get by. 

They named the nettle Pilea cavernicola in reference to its cave-dwelling habit. While it has only just been discovered, the IUCN considers this species vulnerable. Only two populations are known and their proximity to expanding human activity puts them in danger of rapid extinction. 

Photo Credit: Monro & Wei

Further Reading: [1]

A Poop-Eating Pitcher Plant

The aerial pitchers of Nepenthes hemsleyana (http://bit.ly/2hC94fO) are quite unique in that they are not intended to catch insects. Instead, they have evolved as specialized roosts for Hardwicke's woolly bats (Kerivoula hardwickii). This incredible mutualism is quite unique among these tropical carnivores. The bats get a safe place to roost and in return, they deposit nitrogen-rich feces. 

This mutualism is quite remarkable in that the upper pitchers of N. hemsleyana have pretty much forgone insect capture altogether. Despite the obvious benefits of this evolutionary relationship, no one had bothered to quantify the benefits gained by turning insect catching pitchers into bat roosts. That is, until now. 

A team of researchers based out of University of Greifswald in Germany utilized some cunning methods to demonstrate exactly how much N. hemsleyana relies on bat droppings. What they found what quite remarkable. Plants offered only insects not only had fewer leaves, they also exhibited slower growth, reduced photosynthetic capacity, and reduced survival. It would seem that this mutualism has evolved to the point of being obligate. 

It is estimated that around 95% of the nitrogen needs of this plant are met by bat feces alone. As it turns out, nitrogen bound up in insect tissues were mostly unavailable to the plant. This is not the case for nitrogen in bat poop. Nitrogen deposited by bats comes mostly in the form of urea, which degrades into ammonium and is readily absorbed by the pitchers. 

Essentially Nepenthes hemsleyana now relies on bats to capture prey for them. This "ecological outsourcing," as it has been termed, frees the plant from the rigors of having to capture and digest insects on its own, thus saving valuable energy reserves that can be allocated to structures such as leaves, stems, and flowers. Why this species has evolved this strategy is anyone's guess. Perhaps it has to do with the deep shaded forest understory in which it grows. 

Photo Credit: Merlin Tuttle (www.merlintuttle.smugmug.com)

Further Reading: [1]

Shape Changing Flowers Attract Bats

For nectar feeding bats, finding food in a dense tropical rainforest is a complex task. For many years it was thought that nectar feeding bats relied solely on scent to find their food. Unlike insects that move around, flowers are stationary. That all changed once we developed microphones sensitive enough to pick up bat calls.

It turns out, nectar feeding bats utilize different frequencies for echolocation that are primed for resolving finer details than those of their insect feeding cousins. Obviously this works quite well for the bats as they are very important pollinators. Whereas many bat pollinated plants position their flowers in easy to reach places for bats, others take it a step further.

Some plant species couple their floral displays with specialized structures that are prime reflectors for bat sonar. Recently, a species of vine known scientifically as Marcgravia evenia (http://bit.ly/2h358BF) was made famous the world over for the satellite dish shaped leaves it produces just above its inflorescence. However, this species is not alone. Other plants have managed to tap into bat sonar in some very interesting ways. Take, for instance, the bizarrely beautiful blooms of the sea bean.

A member of the legume family, Mucuna holtonii is neotropical in its distribution. It is a vining species that snakes its way up into the canopy. When in flower, the plant produces a stunning pendulum-shaped inflorescence, the end of which is ringed in flowers. Although highly derived for this group, the flowers are nonetheless representative of the family. Their secret to success lies in the single large petal known as the banner or vexillum coupled with some explosive power.

This banner petal acts as a nectar guide, though not in a strictly visual sense. These flowers open at night when nectar feeding bats are out and about. They emit a scent, which likely lets the bats know roughly when and where a meal is available. Unlike bees, however, these bats have no interest in pollen. Instead, they are after the energy-rich nectar reserves that only virgin flowers produce. And they produce quite a bit (relative to their size), upwards of 100 microliters.

Bats that have honed in on the scent are further attracted to the flowers by the shape of the vexillum. Supremely adapted to the specific frequency of these nectar feeding bats, the vexillum of each virgin flower reflects sound waves over a greater range of directions than the clutter of the surrounding forest, thus helping the bats zero in on exactly where they need to be.

Unlike many other bat pollinated flowers, those of M. holtonii cannot be accessed simply by hovering. A bat must land on them in order to access the nectar within. The weight of the bat is what the flowers require to complete the process. When a visiting bat lands on the flower, it triggers an explosive mechanism that snaps the anthers outward, causing pollen to explode from the flower, spattering it all over the bat's back.

Once the bat drinks its fill, nectar production ceases. However, the flowers don't senesce at this point. They still provide a calling card for any other flowers yet to be visited. Despite the fact that they stick around, it has been found that bats are significantly less likely to visit spent flowers. How do they know?

The answer again lies in that banner petal. Once the flowers have been triggered, its shape changes. This results in a change in the way in which bats perceive the flowers via echolocation. Bats soon learn that flowers with this altered shape no longer offer a nectar reward. The plant benefits from this because it reduces the chance that a bat will end up depositing its pollen right back on the flower it came from. It's win win when you think about it. Bats maximize their meals and the plant maximizes its chances of cross pollination.

Photo Credit: Merlin Tuttle

Further Reading: [1] [2] 

The Fuzziest of Flowers

Describing plants can be quite a task for taxonomists. When a new species is discovered, the honor of naming it often goes to the discoverer. At the very least, they have some input. Some folks go for the more traditional rout and give the plant a descriptive name rooted in either Latin or Greek. Others decide to name the plant in honor of a botanist of the past or perhaps a loved one. Still others take a stranger approach in order to immortalize a famous celebrity. However, in doing so they risk taking something away from the species in question.

Instead of a descriptive name that clues you in on specific features of the plant, instead you hit an etymological dead end in which you are stuck with nothing more than a last name. This became quite apparent to University of Alabama botanist John Clark when it was time to name a newly discovered plant species from South America. 

Had things been slightly different, the recently discovered Kohleria hypertrichosa would have been named after Chewbacca. One look at the flowers of this species and you can understand why. The long tubular petals of this gesneriad are covered in dense, fuzzy hair. This is unlike any other plant known to science. The appearance of these odd fuzz balls may seem puzzling at first but considering where this plant was found growing, it quickly becomes apparent that these flowers are a marvelous adaptation in response to climate. 

Kohleria hypertrichosa is only known to grow in a very narrow swath of mountainous cloud forest in the Ecuadorian Andes. At home between elevations of 3,600 and 6,600 feet above sea level, this wonderful gesneriad experiences some pretty low temperatures for a tropical region. It is likely that the thick layer of hairs keeps the flowers a bit warmer than the surrounding air, offering a welcoming microclimate for pollinators. This could potentially make them much more likely to be pollinated in a habitat where pollinators may be in short supply. 

At the end of the day, Clark decided to stick with a more traditional name for this new species. Its scientific name is no less interesting as a result. The specific epithet 'hypertrichosa' is derived from a condition in humans known as hypertrichosis, or werewolf syndrome, in which a person grows excessive amounts of body hair. 

Photo Credit: Andreas Kay [1]

Further Reading: [1]

The Curious Case of a Dancing Plant

Plants aren't generally known for their speed. They tend to move at rates we simply can't perceive. The few species that exhibit rapid movements such as the sensitive plant (Mimosa pudica) and the Venus fly trap (Dionaea muscipula) have become quite famous as a result. Such movements happen in fits and bursts. These plants certainly cannot maintain such activity. However, there is another plant out there whose activity puts these other plants to shame.

Meet the telegraph plant. It has gone by a handful of scientific names since its discovery (Desmodium motorium, D. gyrans, Hedysarum gyrans, Codariocalyx motorius) but that's not why its famous. This Asian legume is renown for its maneuvers. Its compound leaves are quite active. The larger terminal leaflets move up and down throughout the course of a day but its smaller lateral leaflets exhibit rhythmic movements on the scale of minutes.

Perhaps most famously, the leaflets show an increase in movement when exposed to music. Search the web and you will find lots of videos of the telegraph plant "dancing" to a variety of musical styles. Though entertaining, music is not why this plant moves. Having evolved long before music was ever invented, its movement must have its roots in something a bit more natural. Despite how popular such motion has made this species over the past few centuries, their its function has remained a bit of a mystery.

Before we get into the theories, let's take a closer look at exactly how this plant moves. At the base of its leaflets there sits a ring of cells called the "pulvinus." They act a bit like water balloons and thanks to some dedicated work, it has been found that, when stimulated, these cells can quickly move water in and out via osmosis. This causes the cells to either swell or deflate and this is where the movement originates. Now, onto the why...

A relatively recent opinion piece puts forth some of the most interesting theories on telegraph plant movement yet. The author suggests that leaflet movements are defensive in nature. They believe that the leaves could be mimicking butterfly (or some other winged arthropod movements). In doing so, it may convince gravid female insects that this individual plant is already occupied. Such strategies do indeed exist in some plant species, though via physical adornments rather than movements. Another theory this author puts forth is that this could also attract potential predators. By mimicking the movement of a tasty insect, it could entice birds to come in to take a closer look. Once there, they could easily find other herbivores hiding on the plant.

Another possibility related to defense is that the movements are meant to deter herbivory altogether. Studies on other plants have shown that some species can actually detect the sound of an insect chewing on leaves. This causes an uptick in the production of defense compounds. Perhaps the telegraph plant, when sensing sound waves, increases its movements in order to knock away a hungry insect. Certainly a moving meal is less appealing than a stationary one. This is also thought to be the reason for rapid leaflet closure in sensitive plants. Hungry insects have a hard time hanging on to a plant when the leaf suddenly collapses from underneath it.

Another hypothesis is that these movements are meant to increase sun exposure. It has been discovered that far from only responding to music, the leaflets move throughout the day depending on temperature. When temperatures are low, leaflet movements are more vigorous. They eventually slow down if temperatures are high enough. This hypothesis is bolstered by the fact that movements cease once the sun goes down. In a sense, the leaflets seem to be using temperature as a means of detecting whether or not they are getting as much sun on them as possible.

In reality, it very well could be a mix of these ideas. Natural selection works like that. In the end, movement of the leaflets has certainly benefited the telegraph plant whether it be fore defense or just to take advantage of as much sun as possible. Despite centuries of popularity, this awesome little legume still has some secrets tucked away and I kind of like that about it.

Photo Credit: [1]

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

Staying Warm: An Alpine Plant Approach to Reproduction

Things are beginning to cool down throughout the northern hemisphere. As winter approaches, most plant species begin to enter their dormancy period. Very few plants risk wasting their reproductive efforts in the chill of late fall, having gotten most of it out of the way during the warm summer months. This is easy enough for low elevation (and low latitude) plants but what about species living in the high arctic or alpine habitats. Such habitats are faced with cold, harsh conditions year round. How do plants living in these zones deal with reproduction?

These limitations are overcome via physiology. For starters, plants living in such extreme habitats often self pollinate. Insects and other pollinators are too few and far between to rely solely upon them as a means of reproduction. Also, the flowers of most cold weather plants are heliocentric. This means that, as the sun moves across the sky, the flowers track its path so that they are constantly perpendicular to its rays. This maintains maximum exposure to this precious heat source. 

Additionally, many arctic and alpine plants have parabolically shaped flowers. This amplifies the incoming radiation being absorbed by the flower. Experiments have shown that flowers that have been shaded from the heat of the sun had a dismal seed set of only 8% whereas plants exposed to the sun had an elevated seed set of 60%. 

For plants in these habitats, its all about persistence. Low reproductive rates are often offset by extremes in longevity. This is one of the many reasons why hikers must remember to tread lightly in these habitats. Damages incurred by even a single careless hiker can take decades, if not centuries, to recover. 

Photo Credit: [1]

Further Reading: [1]