Pitcher Plant Moths and their Pitcher Plant Homes

Discussions about pitcher plants usually revolve around the fact that they trap and eat insects and other animals. However, there are a handful of organisms out there that turn the table on pitcher plants, reminding us that these botanical carnivores can become food themselves. Spend any amount of time surveying pitcher plant populations in southeastern North America and you are likely to encounter at least one such species of pitcher plant eater.

There are three species of pitcher plant moths in the genus Exyra and all of them would not exist if it were not for pitcher plants in the genus Sarracenia. Whereas E. ridingsii and E. semicrocea are largely restricted to southeastern portions of North America, E. fax can be found as far north as Newfoundland. These three species also vary in their dietary specificity. As you can probably ascertain from its distribution, E. fax is a purple pitcher plant (S. purpurea) but will also feed on the southern pitcher plant (S. rosea) in the southern portions of its range. Exyra ridingsii is also a dietary specialist, feeding only on the pitchers of the yellow pitcher plant (Sarracenia flava). Alternatively, E. semicrocea is a generalist and can be found feeding on a variety of Sarracenia species.

An Exyra caterpillar busy feeding on a Sarracenia flava pitcher.

Both caterpillars and adult moths are physically adapted to living within the slippery interior of the pitcher walls. Microscopic analyses of their feet have revealed specialized morphological adaptations that allow them to cling to the waxy walls of the pitcher. The caterpillars may also benefit from their ability to spin silken lines. Interestingly, the moths are only ever found perched upright in the pitchers. Even when they mate (which also occurs within the pitcher), they do so at a 90 degree angle so that neither partner is facing downward. It is thought that they must remain mostly upright in order for their feet to properly cling to the waxy wall.

Regardless of which pitcher plant they are eating, these three moths all behave similarly throughout their lifecycle. The caterpillars are hatched within a pitcher. Immediately they begin feeding on the wall of the pitcher. They will only eat the interior cells of the pitcher wall, leaving a thin layer of tissue on the outside wall. This makes the pitcher look as if it is covered in translucent, brown windows. At some point in their development, the caterpillars will also spin a layer of silk over the mouth of the pitcher. This protects them from predators like lynx spiders and cuts off the pitchers ability to capture prey (more on this in a bit).

As the caterpillars grow, they will occasionally move to new pitchers. At larger sizes, their feeding damage can be quite extensive, damaging the walls of the pitcher to the point that it loses its structural integrity and folds over. This can also serve to protect the caterpillar from predators while similarly reducing the ability of the plant to capture food. After their fifth larval instar, the caterpillars will move to a new, usually undamaged pitcher. In many instances, they will crawl to the bottom and chew a small hole in the side, draining the pitcher of its digestive fluids. They will then pupate just above the drainage hole.

Signs of Exyra feeding damage.

After a period of time that varies between species, adult moths will emerge. The adults are adorable little critters dressed in shades of yellow and black. They are also very secretive and do not leave the pitchers until nightfall. Even then, they only do so to mate and lay eggs in new pitchers. After mating, the female will lay her eggs just below the mouth of a new pitcher and the cycle begins anew. Amazingly, it has been found that the only other stimulus besides the urge to mate that can coax the moths to leave their pitchers is smoke. This is especially true for the southern species as the bogs in which they live are subject to frequent fires. If they were to remain in the pitchers, it is likely that entire populations would be incinerated.

As terrifying as this sounds for the moths, fire is essential to their lifecycle. The pitcher plant bogs of southeastern North America could not persist without fire. When fires are suppressed, these bogs inevitably fill in with more aggressive vegetation such as swamp titi (Cyrilla racemiflora) or any of the myriad invasive species that grow in this region. As bogs become choked with woody shrubs and trees, pitcher plants and other bog species are choked out to the point that they can completely disappear. Fire in these habitats brings more life than it does death.

A population of Sarracenia flava var. rubricorpora showing signs of a thriving Exyra moth population in the form of damaged and bent over pitchers.

Given that the pitchers of pitcher plants function as both photosynthetic organs and a means to obtain nutrients like nitrogen and phosphorus, it stands to reason that damage from pitcher plant moths could harm the plants over the long term. Indeed, high densities of pitcher plant moths can exact quite a toll on pitcher plant individuals. Evidence from multiple sites has shown that heavily damaged pitcher plants can shrink in size over time, indicating loss of energy reserves. In support of this, some have also found that highly damaged pitcher plants go on to produce more pitchers, which indicates that such individuals are prioritizing more nutrient capture. In ecosystems already defined by nutrient scarcity, the effects of herbivory on these carnivorous plants are likely more severe than they are for plants growing in nutrient-rich environments. However, it should be noted that it is a rare case in which pitcher plant moths exact such a toll on plants as to completely kill the pitcher plants they rely on for survival.

That being said, there is plenty of room for concern over the future of both pitcher plants and moths. Only 3% of the bogs that once existed in southeastern North America remain today. Habitat loss means fewer populations of plants and thus less habitat for the moths (and myriad other lifeforms) that rely on them. For these reasons and more, habitat protection and restoration must be made a high priority moving into the future. Please consider supporting a land conservation/restoration organization in your area!

Further Reading: [1] [2] [3] [4] [5] [6] [7] [8]

Should We Be Calling Aquatic Bladderworts Omnivores Instead of Carnivores?

Photo by Leonhard Lenz licensed under CC BY-NC 2.0

As is so often the case in nature, the closer we start to look at things, the more interesting they become. Take, for instance, the diet of some carnivorous bladderworts (Utricularia spp.). These wonderful organisms cover their photosynthetic tissues in tiny bladder traps that rapidly spring open whenever a hapless invertebrate makes the mistake of coming too close to a trigger hair. The unlucky prey is quickly sucked into the trap and subsequently digested.

This is how most bladderworts supplement their growth. As cool as this mechanism truly is, our obsession with the idea that these plants are strict carnivores has historically biased the kinds of investigations scientists attempt with these plants. Over the last decade or so, closer inspection of the contents of aquatic bladderwort traps has revealed that a surprising amount of plant material gets trapped as well. Most of this material consists of single celled algae. Is it possible that at least some aquatic bladderworts also gain nutrients from all of that “vegetable” matter?

The answer to this question is a bit more nuanced than expected. Yes, it does appear that non-animal material frequently ends up in bladderwort traps. Much of this comes in the form of a wide variety of algae species. What’s more, it does appear that algae are broken down within the traps themselves, suggesting that the bladderworts are actively digesting this material. The main question that needs to be answered here is whether or not the bladderworts actually benefit from the breakdown of algae.

Evidence of a nutritive benefit from algae digestion is mixed. Some studies have found that the bladderworts don’t appear to benefit at all from the breakdown of algae within their traps. Alternatively, others have found that bladderworts may benefit from digesting at least some types of algae. These authors noted that there doesn’t seem to be any benefit in terms of additional nitrogen for the bladderwort but instead suggest that other trace nutrients might be obtained in this way.

One of the biggest hurdles in this line of research arises from the fact that we still don’t fully understand the digestive mechanisms of bladderworts. It is possible that some of the algal degradation within bladderwort traps has nothing to do with digestion at all. Instead, it could simply be that algae stuck in the traps eventually dies and rots away. Another major question raised by these observations is how tiny organisms like single celled algae even make it into the traps in the first place. What we can say for sure is most algae are far too small to actually trigger the bladder traps. As such, algae is either getting into the traps passively via some form of diffusion or they are sucked in when other, larger prey is captured.

Some research has even suggested that the benefit of trapping algae may depend on the habitats in which bladderworts are growing. Bladderworts living in more acidic water have shown to capture far more algae than bladderworts in more neutral or alkaline water. This has to do with acidity. Numerically speaking, there is far less zooplankton living in acidic water than algae, which means algae is more likely to end up in the bladders. It could be that the benefits of algae are thus greater for plants living in places where little zooplankton is available. Certainly more work will be needed before we can call bladderworts omnivores but the idea itself is exciting.

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

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

A Sundew with Catapults

Photo by Mike Bayly licensed by CC BY-NC-SA 2.0

The pimpernel sundew (Drosera glanduligera) is a very special sundew. It is native to parts of southern Australia as well as Tasmania. With a rosette diameter of only 2.5–6 cm (1–2 in), it is a tiny plant. It is also very short lived, living out its entire lifecycle within the span of winter. However, these facts are not what make this species so interesting. This little sundew grows its own catapults that help it capture prey.

Sundews are incredible carnivores. Each of their leaves are decked out in “tentacles” whose tips secrete sticky mucilage. Whether attracted to the leaves on purpose or simply brushing by them on accident, insects find themselves mired down by the mucilage. To make matters worse, the leaves of many sundew species are capable of movement. As the insects struggle, the tentacles bend inwards and the leaves begin to roll up, thus securing the fate of the hapless victim.

Photo by Peterbest1954 licensed by CC BY-SA 4.0

For small sundews, prey capture is a bit tricky. Whereas smaller arthropods like springtails and isopods are easily captured, larger arthropods are often able to wriggle their way free of the leaves of all but the largest species of sundew. Drosera glanduligera is by no means large and that may be why it utilizes a unique method of trapping larger prey.

Along the outside of each leaf are tentacles that are much longer than the rest. They also differ from the typical sundew tentacle in that they are not tipped with sticky mucilage. However, they are more deadly than they look. Each of these long tentacles is essentially a mini catapult lying in wait. Anything unfortunate enough to brush across one of those tentacles is in for a rude awakening.

(A) Each step between 1 and 10 depicts a 5 ms time interval. (B) Speed (blue) and acceleration (red) of the tentacle head during the bending motion.

Withing only a few miliseconds, the tentacle bends upward, catapulting the prey towards the center of the leaf. Each leaf on D. glanduligera is shaped like a spoon with the highest concentration of sticky hairs at the center. By catapulting arthropods into the center of the leaf, they are far less likely to escape. Once immobilized, the plant can go about the digestion process.

It is amazing just how fast these tentacles can move. To see this happen in any detail, one needs a high speed camera. The amazing thing is that experts still aren’t 100% certain how such rapid movement is possible. The leading hypothesis involves a change in water pressure within specific cells at the base of the tentacles. When triggered, water is rapidly transported out of the cells on the surface of the tentacle base. With stress coming from water-filled cells underneath, the base of the tentacle bends quickly.

Amazingly, the cells often rupture after the tentacle is triggered. What’s more, they do not reset. Each tentacle is only good for one catapult. This may seem wasteful for such a short-lived species but D. glanduligera produces leaves throughout the entirety of its short life. Therefore, there are always new traps waiting to be triggered. Also, provided arthropods are caught with enough frequency, the plant is sure to obtain enough nutrients from each meal to fuel flowering and seed set. Pretty remarkable for such a tiny carnivore!

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

Further Reading: [1]

Of Bladderworts & Birds

Photo by Jean and Fred licensed by CC BY 2.0

Bladderworts are as beautiful as they are deadly. Though they are known the world over for their carnivorous bladder traps, their flowers are something to marvel at as well. Bladderworts flower in a range of colors from yellows to whites, purples to reds. What’s more, the variety of shapes and sizes among bladderwort flowers are incredible. Though the vast majority of bladderwort species rely on insects for pollination, at least one species appears to have co-opted a bird for its reproductive needs.

Red coats (Utricularia menziesii) are endemic to a few coastal regions of western Australia. They are not floating aquatic plants like many of their North American cousins, nor do they grow epiphytically like many tropical bladderworts. Red coats are terrestrial in their habit. Moreover, they live in habitats that dry up for good portions of the year. As the soils dry out, red coats die back into tiny corms in which they store energy during their dry dormancy that will fuel growth as soon as rains return and the surrounding soils are once again saturated.

Photo by Jean and Fred licensed by CC BY 2.0

When conditions are right, red coats produce some of the most spectacular flowers of the entire genus. Though other species also produce red flowers, few produce such outlandishly bright blossoms. Moreover, the flowers themselves are rather robust structures complete with a long, tough nectar spur. Their color, form, and proximity to the ground has led more than one author to suggest that birds, not insects, are the main pollinators of this species.

Indeed, it appears that birds are what these flowers are attracting. Not just any bird will do either. It seems that the western spinebill (Acanthorhynchus superciliosus) is wonderfully primed to pollinate this lovely little carnivore. Red is a major attractant for birds and the fact that red coat flowers are presented so close to ground level places at the perfect height for ground-foraging spinebills. Also, the length, curvature, and nectar content of the nectar spur fits the spinebill beak nicely. Birds approach the plants on the ground and dip their long, curved beaks into the flower, picking up and depositing pollen as they go.

The western spinebill (Acanthorhynchus superciliosus). Note the curved beak. Photo by Jean and Fred licensed by CC BY 2.0

This isn’t the only bladderwort to be suspected of bird pollination. At least two others (Utricularia quelchii & Utricularia campbelliana) have been hypothesized to utilize hummingbirds for pollination. However, there is scant evidence for this. Pollination studies can be tricky like that. Without proper observation and study, one simply can’t confirm a particular pollination syndrome.

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

Further Reading: [1]

Encounters With a Rare White-Topped Carnivore

I am not a list maker. Never have been and never will be. That being said, there are always going to be certain plants that I feel I need to see in the wild before I die. The white-topped pitcher plant (Sarracenia leucophylla) was one such plant.

I will never forget the first time I laid eyes on one of these plants. It was at a carnivorous plant club meeting in which the theme had been “show and tell.” Local growers were proudly showcasing select plants from their collections and it was a great introduction to many groups which, at the time, I was unfamiliar with. Such was the case for the taller pitcher plants in the genus Sarracenia. Up until that point, I had only ever encountered the squat purple pitcher plant (S. purpurea).

I rounded the corner to a row of display tables and was greeted with a line of stunning botanical pitfall traps. Nestled in among the greens, reds, and yellows was a single pot full of tremendously white, green, and red pitcher plants. I picked my jaw up off the floor and inquired. This was the first time I had seen Sarracenia leucophylla. At that point I knew I had to see such a beauty in the wild.

More like white and red top…

It would be nearly a decade before that dream came true. On my recent trip to the Florida panhandle, I learned that there may be a chance to see this species in situ. Needless to say, this plant nerd was feeling pretty ecstatic. Between survey sites, we pulled down a long road and parked our vehicle. I could tell that there was a large clearing just beyond the ditch, on the other side of the trees.

The clearing turned out to be an old logging site. Apparently the site was not damaged too severely during the process as the plant diversity was pretty impressive. We put on our boots and slogged our way down an old two track nearly knee deep in dark, tanic water. All around us we could see amazing species of Sabatia, Lycopodiella, Drosera, and so much more. We didn’t walk far before something white caught my eye.

There to the left of me was a small patch of S. leucophylla. I had a hard time keeping it together. I wanted to jump up and down, run around, and let off all of the excited energy that had built up that morning. I decided to reign it in, however, as I had to be extra careful not to trample any of the other incredible plants growing near by. It is always sad to see the complete disregard even seasoned botanists have for plants that are unlucky enough to be growing next door to a species deemed “more exciting,” but I digress.

Sarracenia leucophylla flower. Photo by Noah Elhardt licensed by GNU Free Documentation License [SOURCE]

This was truly a moment I needed to savor. I took a few pictures and then put my camera away to simply enjoyed being in the presence of such an evolutionary marvel. If you know how pitcher plants work then you will be familiar with S. leucophylla. Its brightly colored pitchers are pitfall traps. Insects lured in by the bright colors, sweet smell, and tasty extrafloral nectar eventually lose their footing and fall down into the mouth of the pitcher. Once they have passed the rim, escape is unlikely. Downward pointing hairs and slippery walls ensure that few, if any, insects can crawl back out.

What makes this species so precious (other than its amazing appearance) is just how rare it has become. Sarracenia leucophylla is a poster child for the impact humans are having on this entire ecosystem. It can only be found in a few scattered locations along the Gulf Coast of North America. The main threat to this species is, of course, loss of habitat.

A large conservation population growing ex situ at the Atlanta Botanical Garden.

Southeastern North America has seen an explosion in its human population over the last few decades and that has come at great cost to wild spaces. Destruction from human development, agriculture, and timber production have seen much of its wetland habitats disappear. What is left has been severely degraded by a loss of fire. Fires act as a sort of reset button on the vegetation dynamics of fire-prone habitats by clearing the area of vegetation. Without fires, species like S. leucophylla are quickly out-competed by more aggressive plants, especially woody shrubs like titi (Cyrilla racemiflora).

Another major threat to this species is poaching, though the main reasons may surprise you. Though S. leucophylla is a highly sought-after species by carnivorous plant growers, its ease of propagation means seed grown plants are usually readily available. That is not to say poaching for the plant trade doesn’t happen. It does and the locations of wild populations are best kept secret.

Sarracenia leucophylla habitat. Photo by Brad Adler licensed by CC BY-SA 2.5 [SOURCE]

The main issue with poaching involves the cut flower trade. Florists looking to add something exotic to their floral displays have taken to using the brightly colored pitchers of various Sarracenia species. One or two pitchers from a population probably doesn’t hurt the plants very much but reports of entire populations having their pitchers removed are not uncommon to hear about. It is important to realize that not only do the pitchers provide these plants with much-needed nutrients, they are also the main photosynthetic organs. Without them, plants will starve and die.

I think at this point my reasons for excitement are pretty obvious. Wandering around we found a handful more plants and a few even had ripening seed pods. By far the coolest part of the encounter came when I noticed a couple damaged pitchers. I bent down and noticed that they had holes chewed out of the pitcher walls and all were positioned about half way up the pitcher.

I peered down into one of these damaged pitchers and was greeted by two tiny moths. Each moth was yellow with a black head and thick black bands on each wing. A quick internet search revealed that these were very special moths indeed. What we had found was a species of moth called the pitcher plant mining moth (Exyra semicrocea).

An adult pitcher plant mining moth (Exyra semicrocea) sitting within a pitcher!

Amazingly, the lives of these moths are completely tied to the lives of the pitcher plants. Their larvae feed on nothing else. As if seeing this rare plant wasn’t incredible enough, I was witnessing such a wonderfully specific symbiotic relationship right before my very eyes.

Fortunately, the plight of S. leucophylla has not gone unnoticed by conservationists. Lots of attention is being paid to protecting remaining populations, collecting seeds, and reintroducing plants to part of their former range. For instance, it has been estimated that efforts to protect this species by the Atlanta Botanical Garden have safeguarded most of the genetic diversity that remains for S. leucophylla. Outside of direct conservation efforts, many agencies both public and private are bringing fire back into the ecology of these systems. Fires benefit so much more than S. leucophylla. They are restoring the integrity and resiliency of these biodiverse wetland habitats.

LEARN MORE ABOUT WHAT PLACES LIKE THE ATLANTA BOTANICAL GARDEN ARE DOING TO PROTECT IMPORTANT PLANT HABITATS THROUGHOUT THE SOUTHEAST AND MORE.

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

A Poop-Loving Moss Discovered Living on Poop-Eating Pitcher Plants

Poop mosses are strange to say the least. They hail from the family Splachnaceae and most live out their entire (short) lives growing on poop. Needless to say, they are fascinating plants. Recently, one species of poop moss known to science as Tayloria octoblepharum was discovered growing in Borneo for the first time. As if this range expansion wasn’t exciting enough, their growing location was very surprising. Populations of this poop-loving moss were found growing in the pitchers of two species of poop-eating pitcher plants in the genus Nepenthes!

The pitcher of Nepenthes lowii both look and function like a toilet bowl. Photo by JeremiahsCPs licensed under the GNU Free Documentation License

The wide pitcher mouth of Nepenthes macrophylla offer a nice seating area for visiting tree shrews.

The pitchers of both Nepenthes lowii and N. macrophylla get a majority of their nutrient needs not by trapping and digesting arthropods but instead from the feces of tree shrews. They have been coined toilet pitchers as they exhibit specialized adaptations that allow them to collect feces. Tree shrews sit on the mouth of the pitcher and lap up sugary secretions from the lid. As they eat, they poop down into the pitcher, providing the plant with ample food rich in nitrogen. Digestion is a relatively slow process so much of the poop that enters the pitcher sticks around for a bit.

During a 2013 bryophyte survey in Borneo, a small colony of poop moss was discovered growing in the pitcher of a N. lowii. This obviously fascinated botanists who quickly made the connection between the coprophagous habits of these two species. On a return trip, more poop moss was discovered growing in a N. macrophylla pitcher. This population was fertile, indicating that it was able to successfully complete its life cycle within the pitcher environment. It appears that these two toilet pitchers offer ample niche space for this tiny, poop-loving moss. If this doesn’t convince you of just how incredible and complex the botanical world is, I don’t know what will!

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

Further Reading: [1]

Pitcher Plants with a Taste for Salamanders?

Photo by Chris Moody licensed under CC BY-NC 2.0

The thought of a carnivorous plant trapping and digesting a vertebrate may seem more like fiction than reality. Though rumors have circulated over the years that some pitcher plants have a taste for animals larger than an insect, this has been hard to prove as evidence has been notoriously lacking. That is not to say it does not happen from time to time. Small mammals have indeed been found in the pitchers of some of the larger tropical pitcher plants in the genus Nepenthes. Still, these seem more incidental than regular. However, recent observations from Canada suggest that vertebrates may actually make up a bigger part of the menu of some pitcher plants than we previously thought at least under certain circumstances.

The observations were made in Algonquin Provincial Park, Ontario. The carnivore responsible is North America’s most abundant pitcher plant - the purple pitcher plant (Sarracenia purpurea). In late summer of 2017, researchers discovered that some pitchers contained recently metamorphosed salamanders. Some of the salamanders were alive but a few others were dead and undergoing digestion. This was very exciting because despite plenty of study, there has been almost no substantiated evidence of vertebrate prey capture in the purple pitcher plant.

Subsequent surveys were done to figure out if the purple pitcher plants were indeed capturing salamanders on a regular basis or if the salamanders were one-off events. It turns out that, at least for the pitcher plants growing in this bog, salamanders may make up a considerable proportion of their prey! Researchers found that recently metamorphosed spotted salamanders were present in nearly 20% of the pitcher plants they surveyed!

Not all of the salamanders they found were dead. Some were found in a relatively lively state, retreating down into the bottom of the pitcher whenever they were disturbed. Some of the larger dead specimens showed signs of putrefaction, which is probably because they were simply too large to be properly digested. Still, many of the dead salamanders showed signs of digestion, which suggests that the plants are in fact benefiting from salamander capture. In fact, it has been estimated that a single salamander could contribute as much nitrogen to the pitcher plant as the entire contents of three pitchers combined.

Taken together, the team found enough evidence to suggest that salamanders not only make up a portion of the pitcher plants’ diet in this bog, but also that pitcher plants are a significant source of mortality for young salamanders in this system. How the salamanders are caught is up for some debate. It could be that the salamanders are looking for a safe, wet place to hide, however, the complexity of the bog habitat means that there is no shortage of safe places for a young salamander to hide that won’t end in death.

It could also be that salamanders are attracted to all of the invertebrates that these plants capture or that salamanders are accidental victims, having fallen into the trap randomly as they explore their habitat. However, some pitchers not only contained more than one salamander, the plants position and stature within the bog means that most salamanders would have had to actively climb up and into the pitcher in order to end up inside. It very well may not be random chance after all. Certainly this will require more tests to say for sure.

What we can say for now is that within the confines of this Algonquin bog, salamanders are being trapped and digested by the purple pitcher plant. How much of this is unique to the circumstances of this particular bog and how much of this is something going on in other areas within the range of the purple pitcher plant is a subject for future research. It is possible that vertebrate prey may be more common among carnivorous plants than we ever thought!

Photo Credits: [1] [2]

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

The Floating Bladderwort

A carnivorous plant species that uses its radially arranged stolons like tiny pontoons to float at the waters surface may sound like something out of a science fiction novel. However, it is a very real strategy  adopted by one of the coolest carnivorous plants in North America. Utricularia inflata is one of the largest species of floating bladderwort on this continent and it is a species worth knowing.

Sometimes referred to as the swollen bladderwort, this species enjoys a native range that extends through much of the southeastern United States. For most of the year it exists in a state quite similar to other aquatic bladderworts. It has no true roots or leaves. Instead it produces a long, filiform stolon covered in tiny filaments that act as leaves with bladder traps situated at their tips. It sits in the water  column, gobbling up anything small and unfortunate enough to stumble into it.

Photo by Daiju Azuma licensed under CC BY-SA 2.5

When flowering time approaches, these aquatic carnivores begin producing a different kind of stolon. Arranged like spokes on a wheel, the plant puts out swollen, air-filled stolons that float at the waters surface. These structures support the inflorescence. Flowers are bright yellow and resemble those of many other bladderwort species. Entire bodies of water can literally erupt in a sea of yellow bladderwort flowers when the right conditions present themselves.

View fullsize

Photo by Adam Arendell licensed under CC BY-NC 2.0

As mentioned, this species is carnivorous. It uses tiny bladder traps to suck in unsuspecting prey. Their diet is varied and includes pretty much anything that can fit into its bladder traps. One research paper reports both animal (rotifers, cladocerans, copepods, annelids, rhizopodeans, as well as small insects) and "plant" (Bacillariophyta, Chlorophyta, Cyanophyta, and Euglenophyta) prey.

Unfortunately these plants have been introduced far outside of their native range. In many areas they are becoming prevalent enough to be considered invasive. For instance, research done in the Adirondack Mountains of New York found that the presence of introduced populations of U. inflata caused significant changes in nutrient cycling, sediment chemistry, and overall net primary productivity.

This is a very neat species well worth a closer look. That being said, if you are a hobbyist such as myself, it is very important to remember that we should never release a species (no matter how cool it is) into areas where it isn't native.

Photo Credit: Dr. Mark Whitten, [3] [4]

Further Reading: [1] [2]

Gooey Pitcher Fluids

Photo by Shawn Mayes licensed under CC BY-SA 3.0

There seems to be no end to the diversity of colors, shapes, and sizes exhibited by Nepenthes and their pitchers. These wonderful carnivorous plants grow these pitchers as a means of supplementing their nutritional needs as the habitats in which Nepenthes are found are lacking in vital nutrients like nitrogen. There are as many variations on the pitcher theme as there are Nepenthes but all function as traps in one form or another. How they trap insects is another topic entirely and some species have evolved incredible means of making sure prey does not escape. Some of my favorites belong to those species that employ sticky mucilage.

Arguably one of the most iconic of this type is Nepenthes inermis. This species is endemic to a small region of Sumatra and, to date, has only been found growing on a handful of mountain peaks in the western part of the country. The specific epithet ‘inermis’ is Latin for ‘unarmed’ as was given in reference to the bizarre upper pitchers of this plant. They look more like toilet bowls than anything carnivorous and indeed, they lack many of the features characteristic of other Nepenthes pitchers such as a peristome and a slippery, waxy coating on the inside of the pitcher walls.

Photo by Alfindra Primaldhi licensed under CC BY 2.0

These may seem like minor details but consider the role these features play in other Nepenthes. A peristome is essentially a brightly colored, slippery lip that lines the outer rim of the pitcher mouth. Not only does this serve in attracting insect prey, it also aids in their capture. As mentioned, the peristome can be extremely slippery (especially when wet) so that any insect stumbling around on the rim is much more likely to fall in. Once inside, a waxy coating on the inside of some pitchers aids in keeping insects down. They simply cannot get purchase on the waxy walls and therefore cannot climb back out. So, for N. inermis to lack both features is a bit strange.

Another interesting feature of N. inermis pitchers is the highly reduced pitcher lid. It hasn’t disappeared completely but compared with other Nepenthes, this pitcher lid barely registers as one. For most Nepenthes, pitcher lids serve multiple functions. For starters, they keep the rain out. Nepenthes are most at home in humid, tropical climates where rain is a daily force to be reckoned with. For many Nepenthes, rain not only dilutes the valuable digestive soup brewing within each pitcher, it can also cause them to overflow and dump their nutritious contents. Pitcher lids can also help in attracting prey. Like the peristome, they are often brightly colored but many also secrete nectar, which insects find irresistible. Lured in by the promise of food, some insects inevitably fall down into the pitcher below.

Looking into the pitcher of Nepenthes inermis. Photo by Shawn Mayes licensed under CC BY-SA 3.0

Considering the importance of such structures, it becomes a little bit confusing why some Nepenthes have evolved away from this anatomy. The question then remains, why would a species like N. inermis no longer produce pitchers with these features? Amazingly, the answer actually lies within the pitcher fluid itself.

Tip over the upper pitchers of N. inermis and you will soon discover that they are filled with an extremely viscous mucilage. It is so viscous that some have reported that when the pitchers are held upside down, the mucilage within can form an unbroken stream of considerable length. Its the viscosity of this fluid that is the real reason that N. inermis is able to capture prey so easily. Insects lured to the traps can catch a drink of the nectar on the tiny lid. In doing so, some inevitably fall down into the pitcher itself.

The upper pitcher of the closely related Nepenthes dubia. Photo by Alfindra Primaldhi licensed under CC BY 2.0

Instead of slippery walls or downward pointing hairs keeping the insects in, the viscous pitcher fluid quickly engulfs the struggling prey. Some have even suggested that the nectar secreted by the tiny lid has narcotic effects on visiting insects, however, I have not seen any data demonstrating this. Once caught in the fluid, insects easily slide their way down into the depths of the pitcher where they can be digested. This is probably why the pitchers are shaped like tiny toilet bowls; their shape allows for a large sticky surface area for insects to get stuck while prey that has already been captured is funneled down to where digestion and absorption takes place. In a way, these types of pitchers behave surprisngly similar to the sticky traps utilized by other carnivorous plants like sundews (Drosera spp.).

The viscous fluid also comes in handy during the frequent rains that blanket these mountains. As mentioned above, rain would quickly dilute most pitcher fluids but not when the pitcher fluid itself is more dense. Water sits on top of the viscous mucilage and when the pitchers become too heavy, they tip over. The water readily pours out but little if any of the pitcher fluid is lost in the process. It seems that species like N. inermis no longer fight the elements but rather have adapted to meet them head on. As such, they no longer have a need for a large pitcher lid.

Nepenthes jamban takes the toilet bowl shape to the extreme. Photo by Alfindra Primaldhi licensed under CC BY 3.0

Nepenthes inermis is not alone in having evolved pitchers like this. Viscous pitcher mucilage is a trait shared by its closest relatives - N. dubia, N. flava, N. jacquelineae, N. jamban, N. talangensis, and N. tenuis, as well as even more distantly related species such as N. rafflesiana. Because prey capture is so important for the fitness of individuals, it is no wonder that so many different forms have evolved within this genus. In fact, many experts believe that variations in the way in which prey is captured and utilized is one of the main reasons why Nepenthes have undergone such a dramatic adaptive radiation.

Sadly, the uniqueness in form and function of these pitchers has landed many of these species on the endangered species list. As if habitat destruction wasn’t already pushing some to the brink, species like N. inermis are being poached at alarmingly unsustainable rates. Due to their limited distributions, most populations simply cannot recover from even moderate levels of harvesting. The silver lining in all of this is that many Nepenthes are extremely easy to grow and propagate provided their basic needs are met. As more and more folks enter into the carnivorous plant hobby, hopefully more and more people will be sharing seeds, cuttings, and tissue cultured materials. In doing so, we can hopefully reduce some of the pressures placed on wild populations.

Photos via Wikimedia Commons

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

Crab Spiders and Pitcher Plants: A Dynamic Duo

Most pitcher plants in the genus Nepenthes seem pretty adept at catching prey. These plants specialize in nutrient-poor soils and their carnivorous habit evolved as a means of supplementing their nutritional needs. Despite the highly evolved nature of their pitfall traps (which are actually modified leaves), Nepenthes aren’t perfect killing machines. In fact, some get a helping hand from seemingly unlikely partners.

Spend enough time reading about Nepenthes in the wild and you will see countless mentions of arthropods hanging around their pitchers. Some of these inevitably become prey, however, there are others that appear to be taking advantage of the plant. Nepenthes don’t passively trap arthropods. Instead, they lure them in with bright colors and the promise of tasty treats like nectar. This is not lost on predators like spiders, who are frequent denizens of pitcher mouths.

Most notable to Nepenthes specialists are some of the crab spiders that frequently haunt Nepenthes traps. These wonderful arachnids sit at the mouth of the pitcher and ambush any insects that try to pay it a visit. Often times both predator and prey fall down into the pitcher, however, thanks to a strand of silk, the spiders easily climb back out with their meal. This may seem like bad news for the pitcher, however, recent research based out of the National University of Singapore has shown that this relationship is not entirely one sided.

By studying the interactions between spiders and pitcher plants both in the lab and in the field, ecologists discovered that at least one species of pitcher plant (Nepenthes gracilis) appears to benefit greatly from the presence of crab spiders. The key to understanding this relationship lies in the types of prey N. gracilis is able to capture when crab spiders are and are not present.

Not only did the presence of a resident crab spider increase the amount of prey in each Nepenthes pitcher, it also changed the types of insects that were being captured. Crab spiders are ambush predators that frequently attack prey much larger than themselves. It may seem as if this is a form of food robbery on the part of the crab spider but the spiders can’t eat everything. When they have eaten their fill, the spiders discard the carcass into the pitcher where the plant can make quick work digesting it for its own benefit.

Over time, simply having a spider hunting on the trap led to a marked increase in the number of insects in each pitcher compared to those without a spider. Even if these meals are already half eaten, the plant still gains nutrients. Additionally, the types of prey captured by pitchers with and without crab spiders changed. The spiders were able to capture and subdue insects like flesh flies, which normally aren’t captured by Nepenthes pitchers. As such, the resident crab spiders make available a larger suite of potential prey than would be available if they weren’t using the pitchers as hunting grounds.

The crab spiders may benefit the pitcher plant in other ways as well. Research on crab spiders has shown that their bodies are covered in pigments that register high in the UV spectrum. Insects can see UV light and often use it as a means of finding flowers as plants often produce UV-specific pigments in their floral tissues. The wide array of UV patterns on flowers are there to guide their pollinators into position. Researchers have documented that insects are actually more likely to visit flowers with crab spiders than those without, which has led to the idea that UV pigments in crab spiders actually act as insect attractants. Visiting insects simply cannot resist the UV stimulus and quickly fall victim to the resident crab spider.

Could it be that by taking up residence on a Nepenthes pitcher, the crab spiders are increasing the likelihood of insects visiting the traps? This remains to be seen as such questions did not fall under the scope of this investigation. That being said, it certainly offers tantalizing evidence that there is more to the Nepenthes-crab spider relationship. More work is needed to say for sure but the closer we look at such interactions, the more spectacular they become!

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

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

A Passionflower With a Taste for Insects?

Photo by B.navez licensed under the GNU Free Documentation License.

For a plant to be considered carnivorous, it must possess one or more traits unequivocally adapted for attracting, capturing, and/or digesting prey. It also helps to demonstrate that the absorption of nutrients has a clear positive impact on growth or reproductive effort. For plants like the Venus fly trap or any of the various pitcher plants out there, this distinction is pretty straight forward. For many other species, the line between carnivorous or not can be a little blurry. Take, for instance, the case of the stinking passionflower (Passiflora foetida).

At first glance, P. foetida seems par for the course as far as passionflowers are concerned. It is a vining species native from the southwestern United States all the way down into South America. It enjoys edge habitats where it can scramble up and over neighboring vegetation. It produces large, showy flowers followed by edible fruits. When the foliage is damaged, it emits a strong odor, earning it the specific epithet “foetida.”

Not until you inspect the developing floral buds of this passionflower will the question of carnivory enter into your mind. Covering the developing flowers and eventually the fruit are a series of feathery bracts, which are covered in glandular hairs. The hairs themselves are quite sticky thanks to the secretion of fluids. As insects crawl across the hairs, they become hopelessly entangled and eventually die. So, does this make P. foetida a carnivore?

Photo by B.navez licensed under the GNU Free Documentation License.

Many different plants produce sticky hairs or glands on their tissues. Often this is a form of defense. Herbivorous insects looking to take a bite out of such a plant either get stuck outright or have their mouth parts completely gummed up in the process. This form of defense seems to work quite well for such plant species so simply trapping insects doesn’t mean the plant is a carnivore. Worth noting, however, is the fact that it appears that many carnivorous plant traits have simply been retooled from defense traits.

The question remains as to what happens to the trapped insects after they are ensnared by P. foetida. Observations in the field suggest that there is more to these sticky hairs than simply defense. This led a team of researchers to look closer at the interactions between P. foetida and insects. What they found is rather fascinating.

It turns out that most of the insects captured by P. foetida bracts are herbivores that would have made an easy meal of the flowers and fruits. However, after getting stuck, the insect bodies quickly decay. Laboratory analyses revealed that indeed, the fluids secreted by the sticky hairs contained lots of digestive enzymes, mainly proteases and acid phosphatases. Still, this does not mean the plant is eating the insects. It makes sense from a defensive standpoint that a plant would not benefit from having lots of rotting corpses stuck to its buds. As such, digesting them removes the possibility of fungal or bacterial attack. To investigate whether P. foetida benefits from trapping insects beyond simply avoiding herbivory, the team needed to know if any nutritional benefit was being had.

Photo by Vvenka1 licensed under CC BY-SA 2.5

The team took amino acids marked with a special carbon isotope and smeared it onto the bracts. Then they waited to see if any of the labelled amino acids showed up in the plant tissues. Indeed they did. The amino acids were absorbed by the bracts and translocated to the  calyx, corolla, anthers, and finally to the developing ovules. This is probably not too surprising  to those of us that spend time growing plants as numerous plant species can uptake at least some nutrients through their leaves. This is why foliar feeding can work as a means of fertilizing potted plants. Nonetheless, these results are enticing as it shows that P. foetida is not only capturing and dissolving insects, it also seems capable of absorbing at least some amino acids from its victims.

So, should we call P. foetida a carnivore? To be honest, I am not sure. Certainly all of the evidence suggests there is more going on than simply defense. However, does garnering the attention of hungry herbivores constitute prey attraction? Certainly other carnivores utilize food deception as a means of prey capture. Does simply being a palatable plant count as a lure? Does absorbing nutrients constitute carnivory? In some instances, yes, however, as mentioned, plenty of plant species can absorb nutrients from organs other than their roots.

I think the main question is whether P. foetida sees a marked increase in growth or reproduction due to the addition of the dead herbivores. What I think we can say is that the sticky bracts surrounding the flowers and fruits serve a dual purpose - defense against herbivores and potentially a nutrient boost as well. If anything, I think this should qualify as a form of protocarnivory.

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

Further Reading: [1] [2]  

The Carnivorous Dewy Pine

Photo by David Eickhoff licensed under CC BY-NC-SA 2.0

The dewy pine is definitely not a pine, however, it is quite dewy. Known scientifically as Drosophyllum lusitanicum, this carnivore is odd in more ways than one. It is also growing more and more rare each year.

One of the strangest aspects of dewy pine ecology is its habitat preferences. Whereas most carnivorous plants enjoy growing in saturated soils or even floating in water, the dewy pine's preferred habitats dry up completely for a considerably portion of the year. Its entire distribution consists of scattered populations throughout the western Iberian Peninsula and northwest Morocco.

Photo by Javier martin licensed under CC BY-SA 3.0

Its ability to thrive in such xeric conditions is a bit of a conundrum. Plants stay green throughout the year and produce copious amounts of sticky mucilage as a means of catching prey. During the summer months, both air and soil temperatures can skyrocket to well over 100°F (37 °C). Though they possess a rather robust rooting system, dewy pines don't appear to produce much in the way of fine roots. Because of this, any ground water presence deeper in the soil is out of their reach. How then do these plants manage to function throughout the driest parts of the year?

During the hottest months, the only regular supply of water comes in the form of dew. Throughout the night and into early morning, temperatures cool enough for water to condense out of air. Dew covers anything with enough surface area to promote condensation. Thanks to all of those sticky glands on its leaves, the dewy pine possesses plenty of surface area for dew to collect. It is believed that, coupled with the rather porous cuticle of the surface of its leaves, the dewy pine is able to obtain water and reduce evapotranspiration enough to keep itself going throughout the hottest months. 

Dewy pine leaves unfurl like fern fiddle heads as they grow. Photo by Mark Freeth licensed under CC BY 2.0

As you have probably guessed at this point, those dewy leaves do more than photosynthesize and collect water. They also capture prey. Carnivory in this species evolved in response to the extremely poor conditions of their native soils. Nutrients and minerals are extremely low, thus selecting for species that can acquire these necessities via other means. Each dewy pine leaf is covered in two types of glands: stalked glands that produce sticky mucilage, and sessile glands that secrete digestive enzymes and absorb nutrients.

Their ability to capture insects far larger than one would expect is quite remarkable. The more an insect struggles, the more it becomes ensnared. The strength of the dewy pines mucilage likely stems from the fact that the leaves do not move like those of sundews (Drosera spp.). Once an insect is stuck, there is not much hope for its survival. Living in an environment as extreme as this, the dewy pine takes no chances.

Photo by Strombus72 licensed under CC BY-SA 4.0

The taxonomic affinity of the dewy pine has been a source of confusion as well. Because of its obvious similarity to the sundews, the dewy pine has long been considered a member of the family Droseraceae. However, although recent genetic work does suggest a distant relationship with Droseraceae and Nepenthaceae, experts now believe that the dewy pine is unique enough to warrant its own family. Thus, it is now the sole species of the family Drosophyllaceae.

Sadly, the dewy pine is losing ground fast. From industrialization and farming to fire suppression, dewy pines are running out of habitat. It is odd to think of a plant capable of living in such extreme conditions as being overly sensitive but that is the conundrum faced by more plants than just the dewy pine. Without regular levels of intermediate disturbance that clear the landscape of vegetation, plants like the dewy pine quickly get outcompeted by more aggressive plant species. Its the fact that dewy pine can live in such hostile environments that, historically, has kept its populations alive and well.

Photo by Javier martin licensed under Public Domain

What's more, it appears that dewy pines have trouble getting their seeds into new habitats. Low seed dispersal ability means populations can be cut off from suitable habitats that are only modest distances away. Without a helping hand, small, localized populations can disappear alarmingly fast. The good news is, conservationists are working hard on identifying what must be done to ensure the dewy pine is around for future generations to enjoy.

Changes in land use practices, prescribed fires, wild land conservation, and incentives for cattle farmers to adopt more traditional rather than industrial grazing practices may turn the table on dewy pine extinction. Additionally, dewy pines have become a sort of horticultural oddity over the last decade or so. As dedicated growers perfect germination and growing techniques, ex situ conservation can help maintain stocks of genetic material around the globe.

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

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

The Bladderwort Microbiome Revealed

Photo by Stefan.lefnaer licensed under CC BY-SA 3.0

The bladderworts (Utricularia spp.) are among the most cosmopolitan groups of carnivorous plants on this planet. Despite their popularity, their carnivorous habits have been subject to some debate. Close observation reveals that prey capture rates are surprisingly low for most species. This has led some to suggest that the bladderworts may be benefiting from more passive forms of nutrient acquisition. To better understand how these plants utilize their traps, a team of researchers decided to take a closer look at the microbiome living within. 

The team analyzed the trap fluid of a handful of floating aquatic bladderwort species - U. vulgaris, U. australis, and U reflexa. In doing so, they uncovered a bewildering variety of microorganisms perfectly at home within the bladderwort traps. Thanks to sophisticated genetic tools, they were able to classify these microbes in order to investigate what exactly they might be doing inside the traps. 

Their findings were quite astonishing to say the least. The traps of these plants harbor extremely rich microbial communities, far richer than the microbial diversity of other carnivorous plant traps. In fact, the richness of these microbial communities were more akin to the richness seen in the rooting zone of terrestrial plants or the gut of a cow. In terms of the species present, the microbial communities of bladderwort traps most closely resembled that of the pitchers of Sarracenia species as well as the guts of herbivorous iguanas.

Photo by Michal Rubeš - http://www.darwiniana.cz/vamr/?page=obrazek&id=914 licensed under CC BY 4.0

The similarities with herbivore guts is quite remarkable. Its not just coincidental either. The types of microbes they found weren't new to science but their function was a bit of a surprise. A large percentage of the bacteria living within the fluid are famously known for producing enzymes that digest complex plant tissues. Similarly, the team found related microbe groups that specialize on anaerobic fermentation. These types of microbes in particular are largely responsible for the breakdown of plant materials in the rumen of cattle.

As it turns out, the microbes living within the traps of these bladderworts are serving a very important purpose for the plant - they are breaking down plant and algae cells that find their way into the traps each time they open and close. In doing so, they give off valuable nutrients that the bladderworts can then absorb and utilize. Let me say that again, the bacteria living in bladderwort traps are digesting algae and other plant materials that these carnivorous plants can then absorb.

Now these bacteria are also responsible for producing a lot of methane in the process. Interestingly enough, the team was not able to detect measurable levels of methane leaving the traps. This would be odd if it wasn't for the community of methane-feeding microbes also discovered living within the traps. The team believes that these organisms metabolize all of the methane being produced before it can escape the traps. 

As remarkable as these findings are, I don't want to give the impression that these carnivorous plants have taken up a strict vegetarian lifestyle. The team also found myriad other microorganisms within the bladder traps, many of them being carnivores themselves. The team also found a rich protist community. A majority of these were euglenids and ciliates. 

These sorts of protists are important microbial predators and the numbers recorded within the traps suggest that they are a rather significant component of these trap communities. As they chase down and consume bacteria and other protists, they release valuable nutrients that the plants can absorb and utilize. Numbers of these predatory protists were much higher in older traps, which have had much more time to accumulate a diverse microbiome. Astonishingly, it is estimated that the protist communities can cycle the entire contents of the bladderwort traps upwards of 4 or 5 times in a 24 hour period. That is some serious turnover of nutrients!

The protists weren't the only predators found within the traps either. There are also a considerable amount of bacterial predators living there as well. These not only cycle nutrients in similar ways to the protist community, it is likely they also exhibit strong controls on the biodiversity within this miniature ecosystem. In other words, they are considered keystone predators of these microcosms.

Also present within the traps were large amounts of fungal DNA. None of the species they found are thought to actually live within the traps. Rather, it is thought that they are taken up as spores blown in from the surrounding environment. Exactly how these organisms find themselves living inside bladderwort traps is something worth considering. The plants themselves are known for being covered in biomfilms. It is likely that many of the organisms living within the traps were those found living on the plants originally. 

Taken together, the remarkable discovery of such complex microbial communities living on and within these carnivorous plants shows just how complex the ecology of such systems really are. Far from the active predators we like to think of them as, the bladderworts nonetheless rely on a mixture of symbiotic orgnaisms to provide them with the nutrients that they need. The fact that these plants are in large part digesting plant and algae materials is what I find most astonishing.

Essentially, one can almost think of bladderworts as plants adorned with tiny, complex cow stomachs, each utilizing their microbial community to gain as much nutrients as they can from their living environment. The bladderworts gain access to nutrients and the microbes get a place to live. The bladderworts really do seem to be cultivating a favorable habitat for these organisms as well. Analysis of the bladder fluid demonstrated that the plants actively regulate the pH of the fluid to maintain their living community of digestive assistants. In doing so, they are able to offset the relative rarity of prey capture. Keep in mind that this research was performed on only three species of bladderwort originating from similar habitats. Imagine what we will find in the traps of the multitude of other Utricularia species.

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

Further Reading: [1]

Evidence Of Carnivory In Teasel

Photo by Isidre blanc licensed under CC BY-SA 4.0

As far as carnivorous plants are concerned, the common teasel (Dipsacus fullonum) seems like a strange fit. Observe this plant up close, however, and you might notice something interesting. Its leaves are perfoliate and form a cup-like depression where they attach to the main stem. Not only does this cup regularly fill with water, it also frequently traps small insects.

Many have speculated over the function of this anatomical trap. Much of this speculation has centered around the idea that it may serve as a form of protection for the flowers located above. Insect herbivores climbing up the stem in search of food instead find a moat of water. Some inevitably fall in and drown in the process. Other hypotheses have been put forward as well including the possibility of something approaching carnivory. 

The idea that common teasel could be, to some degree, carnivorous never really went away. For most of this time it has remained entirely theoretical. There simply was no empirical evidence available to say otherwise. All of that changed with a 2011 study published in PLOS. A research duo finally put this theory to the test in the first ever experiment to see if teasel gains any sort of nutrient benefit from its insect victims.

Dipsacus fullonum (Wild Teasel, Common Teasel). Rainwater is held back in leaves. Photo by Björn Appel licensed under CC BY-SA 3.0

By systematically supplying teasel plants with insect prey, the team was able to look at how plants responded to the addition of a potential meal. They added various levels of insect larvae to some plants and removed them from others. For their study, evidence would come in the form of some sort of physiological response to the feeding treatments. If teasel really is obtaining nutrients from its insect victims, it stands to reason that those nutrients would be allocated to either growth or reproduction.

The resulting data offers the first evidence that teasel may in fact be benefiting from the insect carcasses. Although the team found no evidence that plants supplemented with insects were increasing in overall biomass, they did see a positive effect on not only the number of seeds produced but also their size. In other words, when fed a diet of insects, the plants weren't growing any larger but they were producing larger amounts of heavier seeds. This is a real boon for a plant with a biennial life cycle like teasel. The more healthy seeds they can produce, the better.

As exciting as these finds are, one must temper their expectations. As the authors themselves state in their paper, these findings must be replicated in order to say for certain that the effects they measured were due to the addition of insect prey. Second, no chemical analyses were made to determine if the plants are actively digesting these insects or even how available nutrients may be absorbed. Simply put, more work is needed. Perhaps teasel is a species that, evolutionary speaking, is on its way to becoming a true carnivore. We still can't say for sure. Nonetheless, they have given us the first evidence in support of a theory that went more than a century without testing. It is interesting to think that there is a strong possibility that if someone wants to see a carnivorous plant, they need go no further than a fallow field.

Photo Credits: [1] [2]

Further Reading: [1]

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

Source

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. 

Source

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.

Source

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

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

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]

Convergent Carnivores

Photo by Natalie McNear licensed under CC BY-NC 2.0

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.

[SOURCE]

By examining the digestive fluids produced by Cepholotus as well as many other unrelated carnivorous plant species from around the world, researchers 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]

Bacteria Help the Cobra Lily Subdue Prey

Photo by David Berry licensed under CC BY 2.0

The cobra lily (Darlingtonia californica) is one of North America's most stunning pitcher plants. Native to a small region between northern California and southwestern Oregon, this bizarrely beautiful carnivore lives out its life in nutrient poor, cold water bogs and seeps. Although it resides in the same family as our other North American pitcher plants, Sarraceniaceae, the cobra lily has a unique taxonomic position as the only member of its genus.

It doesn't take much familiarity with this plant to guess that it is carnivorous. Its highly modified leaves function as superb insect traps. Lured in by the brightly colored, tongue-like protrusions near the front tip of the hood, insects find a sweet surprise. These tongue-like structures secrete nectar. As insects gradually make their way up the tongue, they inevitably find themselves within the downward pointing mouth of the pitcher. This is where those translucent spots on the top of the hood come in.

Those translucent spots trick the insects into flying upwards into the light. Instead of a clean getaway, insects crash into the inside of the hood and fall down within the trap. The slippery walls of the pitcher interior make escape nearly impossible but that isn't the only thing keeping insects inside. Research has shown that the cobra lily gets a helping hand from bacteria living within the pitcher fluid.

Unlike other pitcher plants, the cobra lily does not fill its traps with rain water. The downward pointing mouth prevents that from happening. Instead, the pitchers secrete their own fluid by pumping water up from the roots. Although there is evidence that the cobra lily does produce at least some of its own digestive enzymes, it is largely believed that this species relies heavily on a robust microbial community living within its pitchers to do most of the digesting for it. This mutualistic community of microbes saves the plant a lot of energy while also providing it with essential nutrients like nitrogen in return for a safe place to live.

That isn't all the bacteria are doing for this pitcher plant either. As it turns out, the pitchers' microbial community may also be helping the plant capture and subdue its prey. A study based out of UC Berkeley demonstrated that the presence of these microbes helps lower the surface tension of the water, effectively drowning any insect almost immediately.

Some members of the microbial community release special compounds called biosurfactants. Through an interesting chemical/physical process that I won't go into here, this keeps insects from using the surface tension of the water to keep them afloat, not unlike a water strider on a pond. Instead, as soon as insects hit the bacteria infested waters, they break the surface tension and sink down to the bottom of the pitcher where they quickly drown. There is little chance of escape for a hapless insect unlucky enough to fall into a cobra lily trap.

Although plant-microbe interactions are nothing new to science, this example is the first of its kind. Although this prey capture role is very likely a secondary benefit of the microbial community within the pitchers, it certainly makes a big difference for these carnivores living in such nutrient poor conditions.

Read more about the amazing world of carnivorous plants by picking up a copy of my book!

Photo Credit: [1] [2]

Further Reading: [1]

A Digestive "On" Switch

Photo by Luiz licensed under CC BY-NC-ND 2.0

A common thread throughout the world of carnivorous plants is that all hail from nutrient poor environments. That is why they evolved carnivory in the first place, as a way of supplementing their nitrogen and phosphorous needs. For as amazing as their various adaptations are, the evolutionary histories of the world's carnivorous plants are still largely shrouded in mystery. A recent paper published in the Annals of Botany takes a closer look at what goes on inside the pitchers of the tropical pitcher plant Nepenthes alata. What they found is quite amazing.

As it turns out, N. alata seems to be able to regulate the amount of digestive enzymes within its pitchers based on prey availability. This makes a lot of sense. Since these species live in nutrient poor conditions, it would be very wasteful to continuously produce digestive fluids. Instead, the research team found that the genes responsible for the productive of digestive enzymes turn on in response to certain cues. In this case, its the presence of insect tissues, specifically chitin. The addition of insect prey coincided with a 24 to 48 hour burst in digestive enzyme production followed by a gradual decrease as the insects were digested. As interesting as this is, these were not the only findings to come out of this research.

When the researchers looked closely at what kinds of enzymes N. alata were producing, they discovered evidence in support of a long-held hypothesis regarding the evolution of carnivory in plants. The genetic pathways induced by the addition of insect chitin are nearly identical to those seen in plant defense pathways. These pathways also induced the production of a series of proteins known to play a role in plant defense reactions against microbial pathogens. What's more, many of the enzymes N. alata were producing inside their pitchers are classified as defense-related proteins. Taken together, this is strong evidence in support of the hypothesis that carnivory in plants evolved from defense reactions already in place.

This finding comes in the wake of an earlier discovery that showed similar pathways in the traps of the Venus fly trap. This is yet more evidence for the fact that evolution does not always occur via novel pathways. Instead, systems that are already in place are retooled to fit a new set of challenges.

Photo Credit: [1]

Further Reading: [1]

On Lynx Spiders and Pitcher Plants

On the coastal plains of southeastern North America, there exists a wide variety of pitcher plant species in the genus Sarracenia. These plants are the objects of desire for photographers, botanists, ecologists, gardeners, and unfortunately poachers. Far from simply being beautiful, these carnivores are marvels of evolution, each with their own unique ecology.

Pitcher plants are most famous for capturing and digesting insect prey but their interactions with arthropods aren't always in their favor. Browse the internet long enough and you will inevitably find photographs like this one above in which a green lynx spider (Peucetia viridans) can be seen haunting the traps of a pitcher plant. Instead of becoming prey, this is a spider that uses the pitchers to hunt.

I should start by saying this is not an obligate relationship. Lynx spiders can be found hunting on a variety of plant species. Instead, they are more accurately opportunistic robbers, stealing potential meals from the pitcher plants they hunt upon. However, what this relationship lacks in specificity, it makes up for in being really interesting. Sarracenia are not passive hunters. They do not sit and wait for insects to blindly stumble into their traps. Instead, they utilize bright colors and tasty nectar to lure insects to their demise. This is exactly what the lynx spider is using to its benefit. 

The green lynx spider does not spin a web like an orb weaver. It is an ambush predator. They have keen eyesight and will quickly pounce on any insect unfortunate enough to get too close. The reason the spider itself does not become yet another meal for the pitcher plant is because they utilize their silk as an anchor. By attaching one end to the outside of the pitcher, the can safely hunt on the trap without the risk of become prey themselves. In fact, spiders hunting on traps even go as far as to retreat down into the trap if threatened.

Photo Credit: Zachary Ambrose - nccarnivores

Further Reading:

http://bit.ly/2cyXlvS

http://bit.ly/2cyWTxT

The Mountain Sweet Pitcher Plant

I am fascinated by pitcher plants. The myriad shapes, sizes, and colors make them quite a spectacle. Add to that their carnivorous habit and what is not to love? I am used to having to visit bogs or coastlines to see them in person so you can imagine my surprise to learn that a small handful of pitcher plants haunt the mountains of Southern Appalachia.

Sarracenia jonesii is a recent acquaintance of mine. I never knew this species existed until 2016. It is a slender pitcher plant whose traps grow taller and narrower than the purple pitcher plant (S. purpurea) but not nearly as tall and robust as species like S. leucophylla. Regardless of its size, this one interesting carnivore. One unique aspect of its ecology is the habitats in which it grows. What could be more strange than a pitcher plant clinging to sloping granite slabs?

Most mountainous areas don't hold water for very long. Aside from bowls and the occasional lake, gravity makes short work of standing water. In southern Appalachia, this often results in impressive cascades where sheets of water flow over granite outcrops and balds. Where water moves slow enough to not wash soil and moss away, cataract bogs can form. Soils are so thin in these areas that trees and shrubs can't take root, thus keeping competition to a minimum. Because granite is rather inert, nutrients are scarce. All of these factors combine to make prime carnivorous plant habitat.

A cataract bog clinging to the side of a waterfall.

Along the edges of these cataract bogs, anywhere sphagnum and other mosses grow is where S. jonesii finds a home. One would think that growing in such hard-to-reach places would protect this interesting and unique carnivore. Sadly, that is not the case. To start with, S. jonesii was never common to begin with. Native to a small region of North and South Carolina, it is now only found in about 10 locations. 

Habitat destruction both direct and indirect (alterations in hydrology) has taken its toll on its numbers in the wild. To add insult to injury, poaching has become a serious issue. In fact, an all green population of this species was completely wiped out by greedy collectors looking to add something rare to their collection. The good news is that there are dedicated folks working on conserving and reintroducing this plant into the wild. In 2007, conservationists at Meadowview Biological Research Station, with help from the National Fish and Wildlife Foundation Grant, successfully reintroduced a population of S. jonesii to its former range.

Although the future remains uncertain for this species, it nonetheless has captured hearts and minds alike. Hopefully the charismatic nature of this species is enough to save it from extinction. I only wish such dedicated conservation efforts were directed at more imperiled plant species, both charismatic and not. 

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