The Fungus-Mimicking Mouse Plant

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The mouse plant (Arisarum proboscideum) is, to me, one of the most charming aroids in existence. Its small stature and unique inflorescence are a joy to observe. It is no wonder that this species has attained a level of popularity among those of us who enjoy growing oddball plants. Its unique appearance may be reason enough to appreciate this little aroid but its pollination strategy is sure to seal the deal.

The mouse plant is native to shaded woodlands in parts of Italy and Spain. It is a spring bloomer, hitting peak flowering around April. It has earned the name “mouse plant” thanks to the long, tail-like appendage that forms at the end of the spathe. That “tail” is the only part of the inflorescence that sticks up above the arrow-shaped leaves. The rest of the structure is presented down near ground level. From its stature and position, to its color, texture, and even smell, everything about the inflorescence is geared around fungal mimicry.

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The mouse plant is pollinated by fungus gnats. However, it doesn’t offer them any rewards. Instead, it has evolved a deceptive pollination syndrome that takes advantage of a need that all living things strive to attain - reproduction. To draw fungus gnats in, the mouse plant inflorescence produces compounds that are said to smell like fungi. Lured by the scent, the insects utilize the tail-like projection of the spathe as a sort of highway that leads them to the source.

Once the fungus gnats locate the inflorescence, they are presented with something incredibly mushroom-like in color and appearance. The only opening in the protective spathe surrounding the spadix and flowers is a tiny, dark hole that opens downward towards the ground. This is akin to what a fungus-loving insect would come to expect from a tiny mushroom cap. Upon entering, the fungus gnats are greeted with the tip of the spadix, which has come to resemble the texture and microclimate of the underside of a mushroom.

Anatomy of a mouse plant inflorescence  [SOURCE]

Anatomy of a mouse plant inflorescence [SOURCE]

This is exactly what the fungus gnats are looking for. After a round of courtship and mating, the fungus gnats set to work laying eggs on the tip of the spadix. Apparently the tactile cues are so similar to that of a mushroom that the fungus gnats simply don’t realize that they are falling victim to a ruse. Upon hatching, the fungus gnat larvae will not be greeted with a mushroomy meal. Instead, they will starve and die within the wilting inflorescence. The job of the adult fungus gnats is not over at this point. To achieve pollination, the plant must trick them into contacting the flowers themselves.

Both male and female flowers are located down at the base of the structure. As you can see in the pictures, the inflorescence is two-toned - dark brown on top and translucent white on the bottom. The flowers just so happen to sit nicely within the part of the spathe that is white in coloration. In making a bid to escape post-mating, the fungus gnats crawl/fly towards the light. However, because the opening in the spathe points downward, the lighted portion of the structure is down at the bottom with the flowers.

The leaves are the best way to locate these plants.

The leaves are the best way to locate these plants.

Confused by this, the fungus gnats dive deeper into the inflorescence and that is when they come into contact with the flowers. Male and female flowers of the mouse plants mature at the exact same time. That way, if visiting fungus gnats happen to be carrying pollen from a previous encounter, they will deposit it on the female flowers and pick up pollen from the male flowers all at once. It has been noted that very few fungus gnats have ever been observed within the flower at any given time so it stands to reason that with a little extra effort, they are able to escape and with any luck (for the plant at least) will repeat the process again with neighboring individuals.

The mouse plant does not appear to be self-fertile so only pollen from unrelated individuals will successfully pollinate the female flowers. This can be a bit of an issue thanks to the fact that plants also reproduce vegetatively. Large mouse plant populations are often made up of clones of a single individual. This may be why rates of sexual reproduction in the wild are often as low as 10 - 20%. Still, it must work some of the time otherwise how would such a sophisticated form of pollination syndrome evolve in the first place.

Photo Credit: [1] [2] [3]

Further Reading: [1] [2]

Raphides: A Gnarly Form of Plant Defense

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Take a bite out of a dumbcane (Dieffenbachia spp.) or a pothos (Philodendron spp.) and it won’t be long before your mouth and throat start to burn (please don’t actually do that). Eat enough of it and your symptoms may also include intense numbing, oral irritation, excessive drooling, localized swelling, and possibly even kidney and liver failure (again, please don’t). What you are experiencing is a brutal form of plant defense caused by tiny crystals called raphides.

Raphides are tiny, needle-shaped crystals made up of calcium oxalate. A lot of plants accumulate calcium oxalate. Research has shown that in doing so, plants are able to sequester excess calcium in their cells. Many plant lineages then use that calcium oxalate to make raphides. Not all raphides come in the form of needle-like crystals. Often they are ‘H’ shaped or even twinned. Others are blunt, kind of like tiny crystalline cigars.

Cigar-shaped raphides found in the tissues of the polka dot plant ( Hypoestes phyllostachya ).

Cigar-shaped raphides found in the tissues of the polka dot plant (Hypoestes phyllostachya).

How raphides form within the plant is rather fascinating. As far as we can discern, raphide crystals form in vacuoles of specialized cells called “idioblasts.” It is thought that an exquisitely controlled scaffolding or matrix shapes the biomineralization process. To the best of my knowledge, no one has been able to reproduce this process in a laboratory setting. For now, plants are the undeniable masters of raphide manufacturing.

Within the cells, raphides are often associated with acrid and toxic proteins. Together, they comprise one hell of a defense against herbivory. Raphides are only the first part of the defensive equation. When plant tissues containing raphides are damaged, usually by chewing, the raphides shoot out of the idioblasts and into the oral cavity of the herbivore. This is where their needle shape comes in.

Needle-like raphides extracted from the leaves of an  Epipremnum  species.

Needle-like raphides extracted from the leaves of an Epipremnum species.

Raphides wreak havoc on sensitive tissues. They literally act like tiny needles, cutting into and tearing the lining of the mouth, esophagus, and gut. This is only half of the story though. As mentioned, raphides are often packed in with acrid and toxic proteins. The laceration caused by the raphides allows these compounds to enter into the wounds. This is where things can get especially nasty. If the proteins are toxic enough, the herbivore now has far more to worry about than simply the burning sensation.

Raphides are not produced in equal amounts in all tissues. Stems tend to have more than leaves, but raphide content in leaves has also shown to be a function of leaf size. Raphides also differ from species to species. Not all plants that produce raphides produce them in the same shape and quantity. Still, more than 200 plant families contain species that have evolved this form of defense and many of our most prized houseplants fall into this category. However, this should not scare you away from these plants. Provided you or your loved ones don’t go nibbling on the leaves or stems, all will be fine. If anything, this remarkable form of plant defense should earn these plants even more respect than they already get.

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

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

Meet the Crypts

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If you have ever spent time in an aquarium store, you have undoubtedly come across a Cryptocoryne or two. Indeed, these plants are most famous for their indispensable role in aquascaping freshwater aquaria. As organisms, however, crypts receive considerably less attention. Nonetheless, a handful of dedicated botanists have devoted time and effort to understanding this wonderful genus of tropical Aroids. What follows is a brief introduction to the world of Cryptocoryne plants. 

Cryptocoryne is a genus that currently consists of around 60 - 65 species, all of which are native to tropical regions of Asia and New Guinea. Every few years it seems at least one or two new species are added to this list and without a doubt, more species await discovery. All crypts are considered aquatic to one degree or another. Ecologically speaking, however, species fall into four broad categories based on the types of habitats they prefer.

Cryptocoryne cognata in situ .

Cryptocoryne cognata in situ.

The most familiar crypts grow along the banks of slow-moving rivers and streams and find themselves submerged for a large portion of their life. Others grow in seasonally flooded habitats and experience a pronounced dry season. These species usually go dormant until flood waters return. Still others can be found growing in swampy forested habitats, often in acidic peat swamps. Finally, a few crypts have adapted to living in tidal zones in both fresh and brackish waters.

Like all aquatic plants, crypts face a lot of challenges living in water. One of the biggest challenges is reproduction. Despite their aquatic nature, crypts will not flower successfully underwater. If growing submerged, most crypt species reproduce vegetatively via a creeping rhizome. As such, crypts often form large, clonal colonies in both the wild and in aquaria, a fact that has made a few crypts aggressive invaders in places like Florida.

Cryptocoryne wendtii  is one of the most common species in the aquarium trade. Its textured leaves are thought to have a higher surface area, allowing this plant to thrive in shaded aquatic habitats.

Cryptocoryne wendtii is one of the most common species in the aquarium trade. Its textured leaves are thought to have a higher surface area, allowing this plant to thrive in shaded aquatic habitats.

Given proper hydrologic cycles, however, crypts will flower and when they do, it is truly a sight to behold. As is typical of aroids, crypts produce an inflorescence comprised of a spadix with whirls of male and female flowers covered by a decorative sheath called a spathe. This spathe is the key to successful flowering among the various crypt species.

Species like  C. becketti  have become invasive in places like Florida, no doubt thanks to aquarium hobbyists.

Species like C. becketti have become invasive in places like Florida, no doubt thanks to aquarium hobbyists.

If the spathe were to open underwater, the inflorescence would quickly rot. Instead, most crypts seem to have an uncanny ability to sense water levels. At early stages of development, the spathe completely encloses the developing spadix in a water tight package. The tubular spathe continues to grow upward until the top has breached the surface. Consequently, the overall length of a crypt inflorescence is highly variable depending on the water level of its habitat. Crypts living in tidal zones take this a step further. Somehow they are able to time their flowering events to the ebb and flow of the tides, only producing flowers during periods of the month when tides are at their lowest.

Cryptocoryne ligua

Cryptocoryne ligua

With the tip of the inflorescence safely above water, the spathe will finally open revealing their surprisingly complex anatomy and coloration. It is a shame that most crypt growers never get to see such floral splendor in person. The spathe of many crypt species emit a faint but unpleasant odor. Additionally, some species adorn the spathe with fringes that, coupled with stark coloration, is thought to improve the chances of pollinator visitation.

Pollinators are poorly studied among crypts, however, it is thought that small flies take up the bulk of the work. Lured in by the promise of a rotting meal on which they can feed and lay their eggs, the flies become trapped inside the long tube of the spathe. Like the pitfall traps of a pitcher plant, the inner walls of the spathe are coated in a waxy substance that keeps the insects from crawling out before they do their job.

In general, the female flowers mature first. If the insect inside has visited a crypt of the same species the day before, it is likely carrying pollen and thus deposits said pollen onto the stigmas of the current crypt. After the female flowers have had a chance at being fertilized, the male flowers then mature. The insects inside are then dusted with new pollen, the walls of the spathe lose their slippery properties, and the insects are released in hopes of repeated the process again.

The fruit of a  Cryptocoryne  is called a syncarp.

The fruit of a Cryptocoryne is called a syncarp.

To the best of my knowledge, most crypts are not self-compatible. Instead, plants must receive pollen from unrelated individuals to set seed. Because large crypt colonies are often made up of clones of a single mother plant, sexual reproduction can be rather infrequent among the various species. Nonetheless sexual reproduction does occur and the seeds are produced in a different way than most other aroids. Instead of berries, crypts produce their seeds in a aggregated collection of fruits called a syncarp. When ripe, the syncarp opens like a little star and the seeds float away on the current.

One species, Cryptocoryne ciliata, takes seed production to a whole different level by producing viviparous seeds. Before the syncarp even opens, the seeds actually germinate on the mother plant. In this way, tiny seedlings complete with roots and leaves are released instead of seeds. Seedlings have a much greater surface area than seeds and readily get stuck in mud as well as other aquatic vegetation. In this way, C. ciliata offspring get a jump start on the establishment process. It is no wonder then that C. ciliata has one of the widest distributions of any of the crypt species.

Cryptocoryne ciliata

Cryptocoryne ciliata

Despite plenty of overlap among the ranges of various crypt species, the genus displays an amazing array of variation. Some have likened crypts to Araceae's version of Darwin's finches in that the unique ecology of each species appears to have created barriers to species introgression. Though hybrids do occur, each crypt seems to maintain its own niche via a unique habitat requirement, differing flower phenology, or a specific set of pollinators. It would appear that much can be learned about the mechanics of speciation by studying the various Cryptocoryne and their habits.

Unfortunately, the limited geographic distribution and specific habitat requirements of crypt species is cause for concern. Many are growing more and more rare as human settlements expand and destroy valuable crypt habitat. As popular as some crypts may be in cultivation, many others have proven too idiosyncratic to grow on a commercial level. More work is certainly needed to properly assess populations and bring plants into cultivation as a form of ex situ conservation.

Cryptocoryne cordata  Var. Siamensis 'Rosanervig' is a contoversial variety names recognized by the stark patterns of venation on its leaves.

Cryptocoryne cordata Var. Siamensis 'Rosanervig' is a contoversial variety names recognized by the stark patterns of venation on its leaves.

Proper study is further complicated by the fact that many crypt species are highly plastic. They have to be in order to survive the rigors of their aquatic environment. True species identification can really only be assessed when flowers are present and some populations seem to prefer vegetative over sexual reproduction a majority of the time. A multitude of subspecies exist, though the degree to which they should be formally recognized is up for debate.

I think it is safe to say that Cryptocoryne is a genus worth far more attention than it currently receives. They are without a doubt important components of the ecology of their native habitats and humans would do well to understand them a bit better. With a bit more attention from botanical gardens and other conservation organizations, perhaps the future for many crypts does not have to be so bleak.

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

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

 

The Intriguing Pollination of a Central American Anthurium

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As an avid gardener of both indoors and out, there are few better experiences than getting to see familiar plants growing in the wild for the first time. That experience is made all the better when you find out new and interesting facts about their ecology. On a recent trip to Costa Rica, I was introduced to a wide variety of Anthurium species. I marveled at how amazing these plants look in situ and was taken aback to learn that many produce flowers with intoxicating aromas.

I was also extremely fortunate to be in the presence of some aroid experts during this trip and their knowledge fueled my interest in getting up close and personal with what little time I had with these plants. They were able to ID the plants and introduce me to their biology. One species in particular has been the subject of interest in an ongoing pollination study that has proven to be unique.

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The plant in question is known scientifically as Anthurium acutifolium and it is rather charming once you get to know it. It is a terrestrial plant with relatively large leaves for its overall size. Its range includes portions of lowland Costa Rica and Panama. Its flowers are typical of what one would expect out of this family. They are fused into a type of inflorescence known as a spadix and can range in color from white to green and occasionally red. If you are lucky to visit the spadix between roughly 8:00 AM and 12:30 PM, you may notice a rich scent that, to me, is impossible to describe in words.

It's this scent that sets the stage for pollination in this species. During some down time, University of Vienna grad student Florian Etl discovered that the spadix of A. acutifolium was getting a lot of attention from a particular species of small bee. Closer inspection revealed that they were all males of a species of oil-collecting bee known as Paratetrapedia chocoensis. Now, the females of these oil collecting bees are well known in the pollination literature. They visit flowers that secrete special oils that the females then use to build nests and feed their young. This is why the attention from male bees was so intriguing.

A: A male  P. chocoensis  bee approaching a scented spadix of an inflorescence of  A. acutifolium . B: The abdominal mopping behavior of male  P. chocoensis  oil bees on a spadix. C: Ventral side of the abdomen of a male  P.chocoensis  covered with pollen. D: A male  P. chocoensis  bee on a spadix of an inflorescence of  A. acutifolium , touching the pollen shedding anthers. E: Pubescent region pressed on the surface of  A. acutifolium  during the mopping behavior. F: A scented inflorescence of  A. acutifolium  with three male  P. chocoensis  individuals. G: Image of the abdomen of a male  P.chocensis  in lateral view showing the conspicuous pubescent region. ( SOURCE )

A: A male P. chocoensis bee approaching a scented spadix of an inflorescence of A. acutifolium. B: The abdominal mopping behavior of male P. chocoensis oil bees on a spadix. C: Ventral side of the abdomen of a male P.chocoensis covered with pollen. D: A male P. chocoensis bee on a spadix of an inflorescence of A. acutifolium, touching the pollen shedding anthers. E: Pubescent region pressed on the surface of A. acutifolium during the mopping behavior. F: A scented inflorescence of A. acutifolium with three male P. chocoensis individuals. G: Image of the abdomen of a male P.chocensis in lateral view showing the conspicuous pubescent region. (SOURCE)

Males would land on the spadix and begin rubbing the bottom of their abdomen along its surface. In doing so, they inevitably picked up and deposited pollen. To date, such behavior was unknown among male oil bees. What exactly were these male bees up to?

As it turns out, the males were collecting fragrances. Close inspection of their morphology revealed that each male has a small patch of dense hairs underneath their abdomen. The males are definitely not after fatty oils or nectar as A. acutifolium does not secrete either of these substances. Instead, it would appear that the male oil bees are there to collect scent, which is mopped up by that dense patch of hairs. Even more remarkable is the fact that in order to properly collect these fragrance compounds, the bees are likely using solvents that they have collected from other flowering plant species around the forest.

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What they are doing with these scent compounds remains a mystery but some potential clues lie in another scent/pollination system. Male orchid bees perform similar scent-collecting activities in order to procure unique scent bouquets. Though the exact function of their scent collecting is not known either, we do know that these scents are used in the process of finding and procuring mates. It is likely that these male oil bees are using them in a similar way.

Taken together, these data suggest that a very specific pollination syndrome involving A. acutifolium and male oil bees has evolved in Central American forests. No other insects were observed visiting the flowers of A. acutifolium and the scents only ever attracted males of these specific oil bees during the hours in which the spadix was actively producing the compounds. This is a remarkable pollination syndrome and one that encourages us to start looking elsewhere in the forest. This, my friends, is why there is no substitute for simply taking the time to observe nature. We must take the time to get outside and poke around because we stand to miss out on so much of what makes our world tick and without such knowledge, we risk losing so much. 

Photo Credits: Florian Etl [1]

Further Reading: [1]

This Isn't Even My Final Form! A Pothos Story

Pothos might be one of the most widely cultivated plants in modern history. These vining aroids are so common that I don't think I can name a single person in my life that hasn't had one in their house at some point or another. Renowned for their hardy disposition and ability to handle extremely low light conditions, they have become famous the world over. They are so common that it is all too easy to forget that they have a wild origin. What's more, few of us ever get to see a mature specimen. The plants living in our homes and offices are mere juveniles, struggling to hang on as they search for a canopy that isn't there.

Trying to find information on the progenitors of these ubiquitous houseplants can be a bit confusing. To do so, one must figure out which species they are talking about. Without a proper scientific name, it is nearly impossible to know which plant to refer to. Common names aside, pothos have also undergone a lot of taxonomic revisions since their introduction to the scientific community. Also, what was thought to be a single species is actually a couple.

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To start with, the plants you have growing in your home are no longer considered Pothos. The genus Pothos seemed to be a dumping ground for a lot of nondescript aroid vines throughout the last century. Many species were placed there until proper materials were thoroughly scrutinized. Today, what we know as a "Pothos" has been moved into the genus Epipremnum. This revision did not put all controversies to rest, however, as the morphological changes these plants go through as they age can make things quite tricky.

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As I mentioned, the plants we keep in our homes are still in their juvenile form. Like all plants, these vines start out small. When they find a solid structure in a decent location, they make their bid for the canopy. Up in a tree in reach of life giving sunlight, these vines really hit their stride. They quickly grow their own version of a canopy that consists of massive leaves nearing 2 feet in length! This is when these plants begin to flower. 

As is typical for the family, the inflorescence consists of a spadix covered by a leafy spathe. The spadix itself is covered in minute flowers and these are the key to properly identifying species. When pothos first made its way into the hands of botanists, all they had to go on were the small, juvenile leaves. This is why their taxonomy had been such a mess for so long. Materials obtained in 1880 were originally named Pothos aureus. It was then moved into the genus Scindapsus in 1908.

Controversy surrounding a proper generic placement continued throughout the 1900's. Then, in the early 1960's, an aroid expert was finally able to get their hands on an inflorescence. By 1964, it was established that these plants did indeed belong in the genus Epipremnum. Sadly, confusion did not end there. The plasticity in forms and colors these vines exhibit left many confusing a handful of species within the group. At various times since the late 1960's, E. aureum and E. pinnatum have been considered two forms of the same species as well as two distinct species. The latest evidence I am aware of is that these two vines are in fact distinct enough to warrant species status. 

The plant we most often encounter is E. aureum. Its long history of following humans wherever they go has led to it becoming an aggressive invader throughout many regions of the world. It is considered a noxious weed in places like Australia, Southeast Asia, India, Pakistan, and Hawai'i (just to name a few). It does so well in these places that it has been a little difficult to figure out where these plants originated. Thanks to some solid detective work, E. aureum is now believed to be native to Mo'orea Island off the west coast of French Polynesia. 

Epipremnum pinnatum  is similar until you see an adult plant

Epipremnum pinnatum is similar until you see an adult plant

It is unlikely that most folks have what it takes to grow this species to its full potential in their home. They are simply too large and require ample sunlight, nutrients, and humidity to hit their stride. Nonetheless there is something to be said for the familiarity we have with these plants. They have managed to enthrall us just enough to be a fixture in so many homes, offices, and shopping centers. It has also helped them conquer far more than the tiny Pacific island on which they evolved. Becoming an invasive species always seems to have a strong human element and this aroid is the perfect example.

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

Further Reading: [1] [2] [3] 

 

Arums, Orchids and Vines, Oh My!

This week we head into the forests of Illinois to see what late spring botany we can find. This is one of the coolest times of the year to look for plants in temperate North America. 

Producer, Writer, Creator, Host:
Matt Candeias (http://www.indefenseofplants.com)

Producer, Editor, Camera:
Grant Czadzeck (http://www.grantczadzeck.com)

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Artist: Lazy Legs
Track: Molasses
Album: Lazy Legs EP
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The Tiniest Flowers

It is easy to get caught up in grandeur. Finding the largest of something is always fun but what about the smallest? I have talked about the largest flowers in the world (http://on.fb.me/1bnfEbk) but how small can a flower get? The answer lies in one of the most common plants on earth, duckweed.

There are roughly 38 species of duckweed out there and all of them represent pretty much the epitome of flowering plant reductionism. They are little more than a pair or so of leaf-like structures that float at or near the waters surface and the occasional taproot. What is even more striking are the flowers. Whereas most duckweed will reproduce clonally, every once in a while a flower will be produced. One genus, Wolffia, produces the smallest flowers of any duckweed. They are also the smallest flowers known to science. As you can see from the picture, they are nothing more than a couple anthers (A1 and A2) and a pistil (Pi). What's more, the male parts mature and die before the female parts, thus limiting the chances of self fertilization. As one would expect, the fruits produced are also the smallest fruits in the world.

This is all quite interesting considering the fact that DNA analysis places duckweeds in the Araceae family, which is home to the largest single inflorescence in the world (http://on.fb.me/19i6XNX)! That's right, the arum family produces one of the largest groups of flowers in the world as well as the smallest flower and fruit in the world. Another cool fact about duckweed, specifically Wolffia, is that, gram for gram, it produces the same amount of protein as soy beans. Because of this, it is used as a food plant in many places around the world and more countries are waking up to its potential as both a food plant and a phytoremediation species. Pretty neat for such a small plant.

Photo Credit: Patrick Denny

Further Reading:

http://bit.ly/2c9smn9

http://bit.ly/2bPOMgX

http://bit.ly/2bPQw9A

http://bit.ly/2bzTL4I