The Cypress-Knee Sedge

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Sedges (Carex spp.) simply do not get the attention they deserve. I am part of this problem because like so many others, I have breezed over them in vegetation surveys as “just another graminoid.” This is truly a shame because not only are sedges absolutely fascinating organisms, they are immensely important ecologically as well. I am working hard to get to know sedges better so that I too can fully appreciate their place in our ecosystems. One of the coolest specialist sedges I just recently learned about is the so-called cypress-knee sedge (Carex decomposita). For all intents and purposes, this sedge is considered something of an epiphyte!

The cypress-knee sedge has a fondness for growing on wood. Most often you will find it rooted to the buttresses and knees of bald cypress (Taxodium distichum) or the swollen trunk of a swamp tupelo (Nyssa aquatica). It can also be found growing out of rotting logs that float on the surface of the water. It is a long lived species, with individuals having records stretching back through decades of wetland plant surveys. When supplied with the conditions it likes, populations can thrive. That is not to say that it does well everywhere. In fact, it has declined quite a bit throughout its range.

Juvenile cypress-knee sedges establishing in moss along the water line of a bald cypress.

Juvenile cypress-knee sedges establishing in moss along the water line of a bald cypress.

One of the key wetland features that the cypress-knee sedge needs to survive and prosper is a stable water level. If water levels change too much, entire populations can be wiped out either by drowning or desiccation. Even before the sedge gets established, its seeds require stable water levels to even get to suitable germination sites. Each achene (fruit) comes complete with a tiny, corky area at its tip that allows the seeds to float. Floating seeds are how this species gets around. With any luck, some seeds will end up at the base of a tree or on a floating log where they can germinate and grow. If water levels fluctuate too much, the seeds simply can’t reach such locations.

Its dependence on high quality wetlands is one of the major reasons why the cypress-knee sedge has declined so much in recent decades. Aside from outright destruction of wetlands, changes in wetland hydrology can have dire consequences for its survival. One of the major issues for the cypress-knee sedge is boat traffic. Boat wakes create a lot of disturbance in the water that can literally scour away entire populations from the base of trees and logs. Another major threat are changes to upstream habitats. Any alteration to the watersheds of wetland habitats can spell disaster for the cypress-knee sedge. Alterations to creeks, streams, and rivers, as well as changes in ground water infiltration rates can severely alter the water levels in the swamps that this sedge depends on for survival.

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Closeups of the infructescence showing details of the perigynia (fruit).

Closeups of the infructescence showing details of the perigynia (fruit).

Less obvious threats also include changes in plant cover. If the wetlands in which it grows become too dense, the cypress-knee sedge quickly gets out-competed. To thrive, the cypress-knee sedge needs slightly more sunlight than a densely forested wetland can provide. In fact, some have even noted that cypress-knee sedge populations can explode after selective logging of such wetlands. Such explosions have been attributed to not only extra sunlight but also the addition of woody debris, which provides much needed germination sites. That being said, such explosions can only be maintained if woody debris is left in place and further wetland disturbances do not continue.

The plight of the cypress-knee sedge stands as a reminder of just how poorly we treat wetlands around the globe. Aside from providing valuable ecosystem services for the human environment (flood control, water filtration, etc.), wetlands are home to countless unique species. Only by treating wetlands betters and attempting to restore some of what has been lost will we ever do better by wetland species like the cypress-knee sedge. Hopefully by showcasing species like this, people will begin to feel a little more compassion towards the ecosystems on which they depend. Please consider supporting a wetland conservation and restoration initiative in your region!

Photo Credits : LDWF Natural Heritage Program [1] & Paul Marcum (Midwest Graminoides) [2] [3] [4]

Further Reading: [1] [2]


Pitcher Plants with a Taste for Salamanders?

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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!

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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 Dual Benefits of Smelling Like Frightened Aphids

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If you garden, you have probably dealt with aphids. These tiny sap-suckers not only drain the plant of valuable sap, they can also serve as vectors for disease. Plants must contend with the ever-present threat of aphid infestation throughout the growing season and have evolved some amazing defenses against these insects. Recently an incredible form of defense against aphids has been described in pyrethrum (Tanacetum cinerariifolium) and it involves smelling like a frightened aphid colony.

Aphids produce their own alarm pheromones when attacked. Because aphids form large, clonal colonies, these pheromones can help warn their kin of impending doom. Other aphids will also eavesdrop on these alarm signals and will avoid settling in on plants where aphids are being attacked. Aphids aren’t the only ones honing in on these scents either. Aphid predators and parasitoids will also use these compounds to locate aphid colonies. As such, these pheromones are helpful to the host plant because it can mean a reduction in aphid numbers.

An alate (winged) green peach aphid (Myzus persicae).

An alate (winged) green peach aphid (Myzus persicae).

The selection pressured imposed by aphids on plants is so strong that it appears that at least one species of pyrethrum has actually evolved a means of producing these pheromones themselves. Pyrethrum is a member of the aster family (Asteraceae) native to southern portions of Eurasia. Like all flowering plants, its flowers are the most precious organs. They are the key to getting their genes into the next generation and therefore protecting them from herbivore damage is of utmost importance.

It has been discovered that pyrethrums produce an aphid alarm pheromone called ( E )-β-farnesene or EβF for short. The pheromone is not produced in every tissue of the plant but rather it is concentrated near the inflorescence. What’s more, pheromone production is not constant throughout the duration of flowering. Researchers found that it production reaches its peak just before the inflorescence opens to reveal the flowers within.

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The production of EβF in pyrethrum appears to serve a dual function. For starters, it actually results in reduced aphid infestation during the early stages of flowering. When the initial aphid attack begins, these insects consume some of the EβF as they feed and release it as they excrete honeydew. Other aphids detect EβF within the honeydew and will actually avoid the plant, likely due to the perception that the aphids feeding there are already under attack.

That does not mean that predators are not to be found. In fact, the other benefit of producing EβF in the inflorescence is that it appears to lure in one of the most voracious aphid predators on the planet - ladybird beetles. The ladybird beetles are able to detect EβF in the air and will come from far and wide to investigate in hopes of finding a tasty aphid meal. The ladybird beetles were most frequently found on plants during the early stages of floral development, which suggests that EβF production in the floral tissues is the main attractant.

A 7-spot ladybird beetle (Coccinella septempunctata).

A 7-spot ladybird beetle (Coccinella septempunctata).

Interestingly, it has been found that constant production of EβF is less effective at deterring aphids than pulses of EβF. It is thought that just as humans can get used to certain background levels of scent, so too can aphids. If aphids are exposed to high levels of EβF for long periods of time, they simply recognize it as the safe background level and will continue to feed. This may explain why pyrethrum plants only produce EβF for a short period of time during the most crucial stages of floral development. Research like this not only improves our understanding of the myriad ways in which plants defend themselves, it also offers us new avenues for researching more natural ways of defending the plants we rely on from unwanted pests.

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

Further Reading: [1]


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]

A Palm With a Unique Pollination Syndrome

I would like to introduce you to the coligallo palm (Calyptrogyne ghiesbreghtiana). The coligallo palm is a modest palm, living out its life in the understory of wet, tropical forests from Mexico to Panama. To the casual observer, this species doesn’t present much of anything that would seem out of the ordinary. That is, until it flowers. Its spike-like inflorescence is covered in fleshy white flowers that smell of garlic and as far as we know, the coligallo palm is the only palm that requires bats for pollination.

Flowering for this palm occurs year round. At first glance, the inflorescence doesn’t appear out of the ordinary but that is where close observation comes in handy. The more scrutiny they are given, the more strange they appear. As mentioned, the flowers are bright white in color and they smell strongly of garlic. Also, they are protandrous, meaning the male flowers are produced before the female flowers.

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After the male flowers have shed their pollen, there is a period of a few days in which no flowers are produced. Then, after 3 to 4 nights of no flowers, female flowers emerge, ready to receive pollen. Each flower only opens at night and does not last for more than a single evening. Protandry is an excellent strategy to avoid self-pollination. By separating male and female flowers in time, each plant can assure that its own pollen will not be deposited back onto its own stigmas. The fact that the coligallo palm flowers year-round means that there is always a receptive plant somewhere in the forest.

The oddities do not end there. Both male and female flowers are covered in a fleshy tube that must be removed for pollination to occur successfully. Removal of the tube is what actually exposes the reproductive organs and allows pollen transfer to occur. Often times, the flowers of the coligallo palm are dined upon by katydids and other insect herbivores. This does not result in pollination as they completely destroy the flower as they eat. Considering the success of this plant across its range, it stands to reason that something else must provide ample pollination services.

Two species of bat visiting coligallo palm inflorescences: A) A perching  Artibeus  bat feeding on male flowers and B) a hovering  Glossophaga  bat feeding on female flowers.

Two species of bat visiting coligallo palm inflorescences: A) A perching Artibeus bat feeding on male flowers and B) a hovering Glossophaga bat feeding on female flowers.

As it turns out, bats are that pollinator. The job of pollination is not accomplished by a single species of bat either. A few species have been observed visiting the inflorescences. Apparently the bright color and strong odor of the flowers acts as a calling card for flower-feeding bats throughout these forests. Interestingly, the feeding mechanism of each species of bat differs as well. Some bats hover at the inflorescence like hummingbirds, chewing off the fleshy tube from individual flowers as they go. Other bats prefer to perch on the inflorescence itself, crawling all over it as they eat. These different feeding behaviors actually result in different levels of pollination. Though both forms do result in seed set, perching bats appear to be the most effective pollinators of the coligallo palm.

The reason for this is due to the fact that perching bats not only spend more time on the inflorescence, their bodies come into contact with far more flowers as they feed. Hovering bats, on the other hand, only manage to contact a few flowers with their snout at a time. So, despite the variety of bats recorded visiting coligallo palms, the perching bats appear to provide the best pollination services.

A coligallo palm infructescence showing signs of ample pollination.

A coligallo palm infructescence showing signs of ample pollination.

The role of perching bats in the ecology of this palm species does not end with pollination either. It turns out, they also play a crucial role in the dispersal of certain mites that live on the palm flowers. Flower mites live on plants and consume tiny amounts of pollen and nectar. As you can imagine, their small size makes it incredibly difficult for them to find new feeding grounds. This is where perching bats come into play.

It was discovered that besides pollen, perching bats also carried considerable loads of flower mites in their fur. The mites crawl onto the bat as they visit one inflorescence and climb off when they visit another. This is called phoresy. The bats are not harmed by these hitchhikers but are essential to the mite lifecycle. Thanks to their bat transports, the mites are able to make it to new feeding grounds far away from their original location. Though little is known about these mites, it has been suggested that the mites living on the coligallo palm are unique to that species and probably feed on no other plants.

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

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




Botanical Buoys

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American featherfoil (Hottonia inflata) is a fascinating aquatic plant. It can be found in wetlands ranging from the coastal plains of Texas all the way up into Maine. Though widespread, American featherfoil is by no means common. Today I would like to introduce you to this gorgeous member of the primrose family (Primulaceae).

American featherfoil may look like a floating plant but it is not. It roots itself firmly into the soil and spends much of its early days as a vegetative stem covered in wonderful feathery leaves. It may be hard to find during this period as no part of it sticks above the water. To find it, one must look in shallow waters of ponds, ditches, and swamps that have not experienced too much disturbance. More on this in a bit.

American featherfoil lives life in the fast lane. It is what we call a winter annual. Seeds germinate in the fall and by late October, juveniles can be seen sporting a few leaves. There it will remains throughout the winter months until early spring when warming waters signal the growth phase. Such growth is rapid. So rapid, in fact, that by mid to late April, plants are beginning to flower. To successfully reproduce, however, American featherfoil must get its flowers above water.

The need to flower out of water is exactly why this plant looks like it is free floating. The flower stalks certainly do float and they do so via specialized stems, hence the specific epithet “inflata.” Each plant grows a series of large, spongy flowering stalks that are filled with air. This helps buoy the stems up above the water line. It does not float about very much as its stem and roots still anchor it firmly into place. Each inflorescence consists of a series of whorled umbels that vary in color from white to yellow, and even violet. Following pollination, seeds are released into the water where they settle into the mud and await the coming fall.

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As I mentioned above, American featherfoil appreciates wetland habitats that haven’t experienced too much disturbance. Thanks to our wanton disregard for wetlands over the last century or so, American featherfoil (along with countless other species) has seen a decline in numbers. One of the biggest hits to this species came from the trapping of beavers. It turns out, beaver ponds offer some of the most ideal conditions for American featherfoil growth. Beaver ponds are relatively shallow and the water level does not change drastically from month to month.

Historically unsustainable levels of beaver trapping coupled with dam destruction, wetland draining, and agricultural runoff has removed so much suitable habitat and with it American featherfoil as well as numerous wetland constituents. Without habitat, species cannot persist. Because of this, American featherfoil has been placed on state threatened and endangered lists throughout the entirety of its range. With the return of the beaver to much of its former range, there is hope that at least some of the habitat will again be ready for American featherfoil. Still, our relationship with wetlands remains tenuous at best and until we do more to protect and restore such important ecosystems, species like American featherfoil will continue to suffer. This is why you must support wetland protection and restoration in your region!

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

Further Reading: [1] [2]

 

Twinspurs & Their Pollinators

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Garden centers and nurseries always have something to teach me. Though I am largely a native plant gardener, the diversity of plant life offered up for sale is always a bit mind boggling. Perusing the shelves and tables of myriad cultivars and varieties, I inevitably encounter something new and interesting to investigate. That is exactly how I came to learn about the twinspurs (Diascia spp.) and their peculiar floral morphology. Far from being simply beautiful, these herbaceous plants have evolved an interesting relationship with a small group of bees.

Diascia whiteheadii

Diascia whiteheadii

The genus Diascia comprises roughly 70 species and resides in the family Scrophulariaceae. They are native to a decent chunk of southern Africa and have adapted to a range of climate conditions. Most are annuals but some have evolved a perennial habit. The reason these plants caught my eye was not the bright pinks and oranges of their petals but rather the two spurs that hang off the back of each bloom. Those spurs felt like a bit of a departure from other single-spurred flowers that I am used to so I decided to do some research. I fully expected them to be a mutation that someone had selectively bred into these plants, however, that is not the case. It turns out, those two nectar spurs are completely natural and their function in the pollination ecology of these plants is absolutely fascinating.

Diascia rigescens

Diascia rigescens

Not all Diascia produce dual spurs on each flower but a majority of them do. The spurs themselves can vary in length from species to species, which has everything to do with their specific pollinator. The inside of each spur is not filled with nectar as one might expect. Instead, the walls are lined with strange trichomes and that secrete an oily substance. It’s this oily substance that is the sole reward for visiting Diascia flowers.

Diascia megathura  (a) inflorescenc with arrows indicating spurs and (b) cross sectioned spur showing the trichomes secreting oil (Photos: G. Gerlach).

Diascia megathura (a) inflorescenc with arrows indicating spurs and (b) cross sectioned spur showing the trichomes secreting oil (Photos: G. Gerlach).

If you find yourself looking at insects in southern Africa, you may run into a genus of bees called Rediviva whose females have oddly proportioned legs. The two front legs of Rediviva females are disproportionately long compared to the rest of their legs. They look a bit strange compared to other bees but see one in action and you will quickly understand what is going on. Rediviva bees are the sole pollinators of Diascia flowers. Attracted by the bright colors, the bees alight on the flower and begin probing those two nectar spurs with each of their long front legs.

A female  Rediviva longimanus  with its long forelegs.

A female Rediviva longimanus with its long forelegs.

If you look closely at each front leg, you will notice that they are covered in specialized hairs. Those hairs mop up the oily secretions from within each spur and the bee then transfers the oils to sacs on their hind legs. What is even more amazing is that each flower seems to have entered into a relationship with either a small handful or even a single species of Rediviva bee. That is why the spur lengths differ from species to species - each one caters to the front leg length of each species of Rediviva bee. It is worth noting that at least a few species of Diascia are generalists and are visited by at least a couple different bees. Still, the specificity of this relationship appears to have led to reproductive isolation among many populations of these plants, no doubt lending to the diversity of Diascia species we see today.

Diascia  'Coral Belle'

Diascia 'Coral Belle'

The female bees do not eat the oils they collect. Instead, they take them back to their brood chambers, feed them to their developing offspring, and use what remains to line their nests. At this point it goes without saying that if Diascia were to disappear, so too would these bees. It is incredible to think of the myriad ways that plants have tricked their pollinators into giving up most, if not all of their attention to a single type of flower. Also, I love the fact that a simple trip to a garden center unlocked a whole new world of appreciation for a group of pretty, little bedding plants. It just goes to show you that plants have so much more to offer than just their beauty.

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

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

The Wacky World of Whisk Ferns

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The whisk ferns (Psilotum spp.) are a peculiar group of plants. If you hang out in greenhouses long enough, you are most likely to encounter them as “weeds” growing in pots with other plants. Though they aren’t often put on display by themselves, the whisk ferns are certainly worth a closer look.

Psilotum comprises two species, the far more common Psilotum nudum and the lesser known P. complanatum. These two species will also hybridize, resulting in Psilotum × intermedium. Together, the whisk ferns make up one of only two genera in the family Psilotaceae (the other being Tmesipteris). They are strange plants to look at as there doesn’t appear to be much to them besides stems. Indeed, their peculiar morphology has earned them a fair share of taxonomic attention over the last century but before we get into that, it is a good idea to take a closer look at their anatomy.

Psilotum nudum  with yellow sporagia.

Psilotum nudum with yellow sporagia.

What we see when we are looking at a whisk fern is the sporophyte generation. Like all sporophytes, its job is to produce the spores that will go on to make new whisk ferns. This part of the whisk fern lifecycle is pretty much all stem. Though these are in fact vascular plants, they do not produce true leaves. Instead, the branching stem takes up all of the photosynthetic work. What looks like tiny leaf-like scales are actually referred to as ‘enations.’ These structures do not contain any vascular tissue of their own. Instead, they bear a type of fused sporangia that house the spores. When mature, these will turn a bright yellow.

Underground, things aren’t much different. Whisk ferns produce a branching rhizome that is covered in hair-like projections called rhizoids. These structures not only help anchor the plant in place, they also function in a similar way to roots. Rhizoids interface with the soil environment allowing the plant to absorb nutrients and water. However, they don’t do this alone. Like so many other plants, whisk ferns partner with mycorrhizal fungi, which vastly increases the amount of surface area these plants have for absorbing what they need. In return, whisk ferns provide the fungi with carbohydrates they produce through photosynthesis. As lovely as this mutualistic relationship sounds, it actually starts off as parasitism.

A  Psilotum  rhizome with hair-like rhizoids.

A Psilotum rhizome with hair-like rhizoids.

When the spores find a suitable place to germinate, they will grow into the other half of the whisk fern lifecycle, the gametophyte. These resemble tiny versions of the rhizome and contain male and female reproductive organs. Living underground, the gametophytes do not photosynthesize. Instead, they completely rely on mycorrhizal fungi for all of their nutritional needs. This can go on for some time until the gametophytes are fertilized and grow a new sporophyte. Then and only then will the plant actually start giving back to the fungi that their lives depend on.

Psilotum complanatum  with its flattened stems.

Psilotum complanatum with its flattened stems.

Because the overall form of the whisk ferns appears so “simplistic.,” many have hypothesized that the genus Psilotum is an evolutionary throwback to the early days of vascular plant evolution. On a superficial level, the whisk ferns do appear to have a lot in common with rhyniophytes, a group of plants that arose during the early Devonian, some 419 to 393 million years ago. A more detailed inspection of the anatomy of each group would reveal that there are some significant and fundamental differences between the two lineages, which I won’t go into here. Also, subsequent molecular work has shown that the whisk ferns reside quite comfortably within the fern lineage and likely represent a sister group to the order that gives us the adder’s tongue ferns (Ophioglossales). It would appear that whisk ferns more accurately represent a reduction in the more “traditional” fern form rather than a holdover from the early days of land plant evolution.

What the genus Psilotum lacks in number of species, it makes up for with its wide distribution. The whisk ferns seem to have conquered most of the tropical and subtropical landmasses on our planet. In fact, I found it incredibly difficult to discern much in the way of a native distribution for these plants. In some areas they are fairly common components of the local flora whereas in others they are considered rare or even threatened. I am sure that at least some of their expansive distribution can be attributed to human assistance as we move soils and plants around the world. To find them in nature, one must look in the cracks of rocks or on the trunks and branches of trees. Though both species can be found growing on trees, P. complanatum in particular seems to prefer an epiphytic lifestyle.

Psilotum complanatum  (left) and  Psilotum nudum  (right) growing epiphytically.

Psilotum complanatum (left) and Psilotum nudum (right) growing epiphytically.

Whether you grow them on purpose, fight them as a greenhouse “weed,” or track them down in the wild, I hope you take a moment to appreciate these oddball plants. The whisk ferns are intriguing to say the least and certainly offer up a unique conversation piece for anyone curious about the botanical world. They are a genus worth admiring.

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

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

A New Case of Lizard Pollination from South Africa

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With its compact growth habit and small, inconspicuous flowers tucked under its leaves, it seems like Guthriea capensis doesn’t want to be noticed. Indeed, it has earned itself the common name of '“hidden flower.” That’s not to say this plant is unsuccessful. In fact, it seems to do just fine tucked in among high-elevation rock crevices of its home range along the Drakensberg escarpment of South Africa. Despite its cryptic nature, something must be pollinating these plants and recent research has finally figured that out. It appears that the hidden flower has a friend in some local reptiles.

Lizard pollination is not unheard of ([1] & [2]), however, it is by no means a common pollination syndrome. This could have something to do with the fact that we haven’t been looking. Pollination studies are notoriously tricky. Just because something visits a flower does not mean its an effective pollinator. To investigate this properly, one needs ample hours of close observation and some manipulative experiments to get to the bottom of it. Before we get to that, however, its worth getting to know this strange plant in a little more detail.

The hidden flower is a member of an obscure family called Achariaceae. Though a few members have managed to catch our attention economically, most genera are poorly studied. The hidden flower itself appears to be adapted to high elevation environments, hence its compact growth form. By hugging the substrate, this little herb is able to avoid the punishing winds that characterize montane habitats. Plants are dioecious meaning individuals produce either male or female flowers, never both. The most interesting aspect of its flowers, however, are how inconspicuous they are.

The hidden flower ( Guthriea capensis )  in situ .

The hidden flower (Guthriea capensis) in situ.

Flowers are produced at the base of the plant, out of site from most organisms. They are small and mostly green in color except for the presence of a few bright orange glands near the base of the style, deep within the floral tube. What they lack in visibility, they make up for in nectar and smell. Each flower produced copious amounts of sticky, sugar-rich nectar. They are also scented. Taken together, these traits usually signal a pollination syndrome with tiny rodents but this assumption appears to be wrong.

Based on hours of video footage and a handful of clever experiments, a team of researchers from the University of KwaZulu-Natal and the University of the Free State have been able to demonstrate that lizards, not mammals, birds, or insects are the main pollinators of this cryptic plant. Two species of lizard native to this region, Pseudocordylus melanotus and Tropidosaura gularis, were the main floral visitors over the duration of the study period.

Pseudocordylus melanotus

Pseudocordylus melanotus

Tropidosaura gularis

Tropidosaura gularis

Visiting lizards would spend time lapping up nectar from several flowers before moving off and in doing so, picked up lots of pollen in the process. Being covered in scales means that pollen can have a difficult time sticking to the face of a reptile but the researchers believe that this is where the sticky pollen comes into play. It is clear that the pollen adheres to the lizards’ face thanks to the fact that they are usually covered in sticky nectar. By examining repeated feeding attempts on different flowers, they also observed that not only do the lizards pick up plenty of pollen, they deposit it in just the right spot on the stigma for pollination to be successful. Insect visitors, on the other hand, were not as effective at proper pollen transfer.

Conspicuously absent from the visitation roster were rodents. The reason for this could lie in some of the compounds produced within the nectar. The team found high levels of a chemical called safranal, which is responsible for the smell of the flowers. Safranal is also bitter to the taste and it could very well serve as a deterrent to rodents and shrews. More work will be needed to confirm this hypothesis. Whatever the case, safranal does not seem to deter lizards and may even be the initial cue that lures them to the plant in the first place. Tongue flicking was observed in visiting lizards, which is often associated with finding food in other reptiles.

Male flower (a) and female flower (b). Note the presence of the orange glands at the base.

Male flower (a) and female flower (b). Note the presence of the orange glands at the base.

Another interesting observation is that the color of the floral tube and the orange glands within appear to match the colors of one of the lizard pollinators (Pseudocordylus subviridis ). Is it possible that this is further entices the lizards to visit the flowers? Other reptile pollination systems have demonstrated that lizards appear to respond well to color patterns for which they already have some sort of sensory bias. Is it possible that these flowers evolved in response to such a bias? Again, more work will be needed to say for sure.

By excluding vertebrates from visiting the flowers, the team was able to show that indeed lizards appear to be the main pollinators of these plants. Without pollen transfer, seed set is reduced by 95% wheres the additional exclusion of insects only reduced reproductive success by a further 4%. Taken together, it is clear that lizards are the main pollinators of the enigmatic hidden flower. This discovery expands on our limited knowledge of lizard pollination syndromes and rises many interesting questions about how such relationships evolve.

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

Further Reading: [1] [2]

Gooey Seeds

Some seeds can get pretty sticky when water gets involved. Anyone that has ever tried to grow a Chia pet or put chia seeds into water will know what I mean. The seeds of chia (Salvia hispanica) are but one example of seeds that turn gooey with water. The question is, why do they do this? What role does sticky mucilage play in the reproductive cycle of plants around the globe?

It turns out that seed mucilage is an extremely useful trait for many plants. For starters, it can aid in dispersal of seeds. For some plants this simply means being sticky enough to attach to an animal that brushes up against ripe seeds. Mucilage can get stuck on everything from fur to feathers, and even scales. This is yet another form of seed dispersal known as epizoochory. Amazingly, mucilage has shown to be an effective trait for aiding in wind dispersal as well. Such is the case for a small mustard called Alyssum minus. This may seem counterintuitive as one would think that mucilage would weigh a seed down, not send it aloft. In this example, the mucilage forms a tiny wing that surrounds the seed after it has dried out. This wing made out of dried, papery mucilage significantly increased seed dispersal distances on windy days.

Chia seeds in water swell with mucilage, making them look more like frog eggs than seeds.

Chia seeds in water swell with mucilage, making them look more like frog eggs than seeds.

Following dispersal, the role of seed mucilage becomes even more important. Just as it can help seeds stick to potential seed dispersers, the mucilage can also help the seeds stick to the ground. This is especially useful for plants growing in sandy soils that move around a lot easier than more mesic soils. By sticking to the substrate, the mucilage helps the seed maintain good soil to seed contact, which is essential for successful germination. Without it, seeds would easily blow around and never rest in a place long enough to establish.

Adhering the soil also aids in water uptake for the seed. This is a prerequisite for any seed to successfully germinate. However, simply acting like a conduit for water to move from soil to seed isn’t the only advantage the mucilage provides. By swelling up with water, the mucilage acts as a tiny water reservoir, which buffers the seed from potential water stress. Again, this is especially useful for plants growing in xeric habitats. By keeping water around the seed longer than it would be if the seed was directly exposed to the environment, the mucilage speeds up germination and increases the chances of success for the resulting seedling.

Finally, seed mucilage can also protect seeds from predators. Seeds are tiny packets of concentrated nutrients and many animals don’t hesitate to gobble them up. By covering their seeds in sticky mucilage, plants are able to deter at least some potential seed predators like ants from moving and eating their seeds. Also, aside from gumming up the mouths of seed predators, the fact that the seeds stick to the substrate makes them difficult to move. With any luck, seed predators will tire of the chore and move on to easier meals.

Now if we think back to those Chia Pets, we can see why chia seeds are able to germinate on wet ceramic. Their mucilaginous coating not only enables them to adhear to the surface of the structure, it protects them from drying out by holding onto water. It kind of makes you look at those goofy gifts as a subtle way of displaying an interesting evolutionary mechanism in action. 

Photo Credit: [1]  [2]

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

An Intruiguing Relationship Between Ants and Cacti

The extrafloral nectaries of  Pachycereus gatesii  appear as tiny red bumps just below the areole.

The extrafloral nectaries of Pachycereus gatesii appear as tiny red bumps just below the areole.

It’s hard to think of a group of plants that are better defended than cacti. Frequently and often elaborately adorned with vicious spines, these succulents make any animal think twice about trying to take a bite. And yet, for some cacti, spines don’t seem to cut it. A surprising amount of species appear to have taken their defense system to a whole new level by recruiting nature’s most tenacious bodyguards, ants.

Plants frequently have a friend in ants. Spend some time observing ants at work and it’s east to see why. These social insects have numbers and strength on their side. Give ants a reason to be invested in your survival and they will certainly see to it that nothing threatens this partnership. For cacti, this involves the secretion of nectar from specialized tissues called extrafloral nectaries.

Extrafloral nectaries are not unique to cacti. A multitude of plant species produce them, often for similar reasons. Ants love a sugary food source and the more reliable that source becomes, the more adamant an ant colony will be at defending it. The odd thing about cacti is that they don’t seem to have settled on a single type of extrafloral nectary to do the trick. In fact, as many as four different types of extrafloral nectaries have been described in the cactus family.

Ants visiting the extrafloral nectaries covering the developing flowers of  Pilosocereus gounellei .

Ants visiting the extrafloral nectaries covering the developing flowers of Pilosocereus gounellei.

Some cacti secrete nectar from highly modified spines. A great example of this can be seen in genera such as Coryphantha, Cylindropuntia, Echinocactus, Ferocactus, Opuntia, Sclerocactus, and Thelocactus. Such spines are usually short and blunt, hardly resembling spines at all. Other cacti secrete nectar from regular looking spines. This adaptation is odd as there does not seem to be anything special about the anatomy of such spines. Examples of this can be seen in genera such as Brasiliopuntia, Calymmanthium, Harrisia, Opuntia, Pereskiopsis, and Quiabentia. Still others secrete nectar from highly reduced leaves that are found at the base of where the spines originate (the areole). Such leaves have been described in Acanthocereus, Leptocereus, Myrtillocactus, Pachycereus, and Stenocereus. They aren’t easy to recognize as leaves either. Most look like tiny scales. Finally, the fourth type of extrafloral nectary comes in the form of specialized regions of the stem tissue. This has been described in genera such as Armatocereus, Leptocereus, and Pachycereus.

Highly modified spines functioning as extrafloral nectaries in  Ferocactus emoryi.

Highly modified spines functioning as extrafloral nectaries in Ferocactus emoryi.

Seemingly normal spines of  Harrisia pomanensis  secreting nectar.

Seemingly normal spines of Harrisia pomanensis secreting nectar.

Regardless of where they form, their function remains much the same. They secrete a form of nectar which ants find irresistible. The more reliable this food source becomes, the more aggressive ant colonies will be in defending it. This is an especially useful form of defense when it comes to small insect herbivores. Whereas spines deter larger herbivores, they don’t do much to deter organisms that can just slip right through them unharmed. Ants also clean the cacti, potentially removing harmful microbes like fungi and bacteria. Though we are only just beginning to understand the depths of this cactus/ant mutualism, what we have discovered already suggests that the relationship between these types of organisms is far more complex than what I have just outlined above.

For instance, it may not just be sugar that the ants are looking for. In arid desert habitats, water may be the most limiting resource for an ant colony and large, succulent cacti are essentially giant water reservoirs. The key is getting to that water. One study that looked at a species of barrel cactus growing in Arizona called Ferocactus acanthodes found that as spring gives way to summer, the concentration of sugars secreted by the extrafloral nectaries decreases. As a result, the nectar becomes far more watery. Amazingly, ant densities on any given barrel cactus actually increased throughout the summer, despite the fact that the nectar was being watered down. Ants are notoriously prone to desiccation so it stands to reason that water, rather than sugar, is the real prize for colonies hanging out on cacti in such hot desert environments.

The incredible floral display of  Ferocactus wislizeni , a species whose reproductive efforts are affected by the types of ants they attract.

The incredible floral display of Ferocactus wislizeni, a species whose reproductive efforts are affected by the types of ants they attract.

Another interesting observation about the cactus/ant mutualism is that it appears that the identity of the ants truly matters. Though defense is the main benefit to the cactus, research suggests that there is a tipping point in how much such defenses benefit cacti. It has been found that although cacti initially benefit from anti-herbivore and cleaning services, extra aggressive ant species can actually drive off potential pollinators. At least one study has shown that when less aggressive ant species tend cacti, they produce more fruits and those fruits contain significantly more seeds than cacti that have been tended by extremely aggressive ant species. This is especially concerning when we think about the growing issue of invasive ants. As more and more non-native ant species displace native ants, this could really tip the balance for some cactus species.

Despite all of the interesting things we have learned about extrafloral nectaries in the family Cactaceae, there are so many questions yet to be answered. For starters, we still do not know how many different taxa produce them in one form or another. It is likely that closer inspection, especially of rare or poorly understood groups, will reveal that far more cacti produce some type of extrafloral nectary. Also, we know next to nothing about the anatomy of the different types of nectaries. How do they differ from one another and how do some, especially those derived from ordinary spines, actually function? Finally, do these nectaries function year round or is there some sort of seasonal pattern to their development and utility. How does this affect the types of ants they attract and how does that in turn affect the survival and reproduction of these cacti? For such a charismatic group of plants as cacti, we still have to much to learn.

Photo Credits: Thanks to Dr. Jim Mauseth and Dr. John Rebman and Dr. Silvia Rodriguez Machado for use of their photos [1] [2] [3]

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

The Prairie Peninsula

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North American prairies are some of the most endangered habitat types on the planet. Once covering vast swaths of the continent representing the arid rain shadow of the Rocky Mountains, the prairies now occupy only 1% of their former range. We have converted most of that land into agriculture and sub-developments. It may surprise many of you to learn that following the retreat of the Pleistocene glaciers, a subset of prairie ecosystem once stretched a lot further east than one would expect for a prairie. This grassland ecosystem ranged far up into the northeast and even met the Atlantic Coast in parts of New Jersey and Long Island. This was known as the prairie peninsula and today its remnants represent some of the rarest prairie ecosystems that North America has left. 

Ecologists believe that the prairie peninsula owed its existence to an intriguing quirk of the climate at that time. During interglacial periods, eastern North America’s climate was much warmer and drier than it is today. Because of this, prairie grasslands were hypothesized to have migrated east, following the recently exposed terminal moraines that the glaciers left in their wake. Moraine soils tend to be composed of unconsolidated till and are quick to drain water,  which provided perfect conditions for prairies to develop. This prairie peninsula preceded the invasion of trees, which now make up the forests that dominate eastern North America. Today we refer to the remnants of this prairie peninsula as "heaths" or "barrens." Despite their rarity, ecologists have long debated whether such habitats are truly echoes of our glacial past or products of a more recent, cultural clearing of the land.

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A relatively recent paper sheds some light on this debate using some pretty clever detective work. The author used a variety of insects, but mainly focused on spittlebugs, to show that these eastern prairies remnants are, indeed, relics of our glacial past. Apparently, insects like leafhoppers, froghoppers, and spittlebugs are often extremely specialized on specific species of plants, mainly grasses. They feed much like aphids do, by sucking the juices out of the plants vascular tissues. Many of these insects are flightless or at least do not travel great distances from where they were born. If one were to find certain species on the eastern prairies, it would provide strong evidence in support of prairie migration from west to east via the glacial moraines.

The evidence suggests exactly that. Eastern pockets of remnant heaths and barrens do in fact host many of these prairie specialists. What is more interesting is that this research has shown that we can track, with some certainty, the migrational patterns of these ecosystems. As expected, the prairies moved in from the west, during an interglacial period much warmer than now. As they moved across the eastern US, they ran into the Appalachian Mountains, which is a formidable barrier to say the least.

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How did the prairies circumvent this obstacle and end up in pockets along the Atlantic coast? Evidence points to sandy sediments in the numerous valleys along the spine of the Appalachians. Most of these sediments no longer exist due to erosion and out-crowding by forests, causing the current disjunction we see in these rare eastern prairie grasslands. It is amazing to me to think that these pockets of  habitat have existed for centuries, despite all the changes we have laid upon the land. These results are a wonderful example of the uniqueness of these habitats and, now more than ever, show us how much these deserve our attention so that maybe they can persist into the future. It also highlights just how special these ecosystems truly are. They are not something created by the hand of man. Instead, these habitats have survived the test of time. Now they must survive us. Support your local land conservancy today!


Map Credit: [1]

Further Reading: [1]

Meeting One of North America's Rarest Oaks

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A post (and photos) by Robbie Q. Telfer

“Every species is a masterpiece, exquisitely adapted to the particular environment in which it has survived.”

-- E.O. mothereffin Wilson

One of the perks of working at The Morton Arboretum is you get to see cool lectures on tree science for free. At one such program, Dr. Mary Ashley from the University of Illinois at Chicago was sharing her research on oak pollen and how far it can travel to fertilize female flowers (far). She looked at not only trees in the Chicago region, but also oaks off the coast of California and in the Chihuahuan Desert of west Texas, as well as throughout Mexico. That latter oak was a shrubby species called Quercus hinckleyi or Hinckley oak. It is able to spread pollen over far distances as well, despite the fact that there are only 123 individuals known to be left. IUCN lists it as Critically Endangered.

As she was telling us this, it occured to me that I would be in West Texas soon to visit my sister-in-law, so afterwards I approached Dr. Ashley and asked if there was any way I could have the coordinates of Q. hinckleyi so that I could visit it, take a selfie, and luxuriate in the presence of something so rare. I made it clear to her that I understood just how important it was to keep this information a secret, because the last thing this relict needs is to be uprooted by poachers. Which I wish wasn’t a concern, but it is.

Dr. Ashley put me in touch with her colleague Janet Backs who graciously shared the coordinates. I could see the plants from Google maps satellite view. There they were. I probably waved at the computer screen sheepishly.

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As I waited for my time to bask in the majesty of botanical greatness, I consulted my copy of Oaks of North America (1985) by Howard Miller and Samuel Lamb to see what the entry for hinckleyi said.

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Notably, it mentions that “This is another of the oaks with no specific value, except as a curiosity.” More on that later.

After much anticipation, the time was upon us. I decided to drive out to the plants in my rental first thing in the morning after getting to Texas. The Chihuahuan Desert is an astounding place that my Illinoisan eyes weren’t altogether prepared for. It is perhaps the most biodiverse desert in the world, and compared to our prairies, woodlands, and wetlands, it feels like a different planet. Some of the cooler plants I got to see were tree cholla (Cholla sp.), Havard’s century plant (Agave havardiana), Wright’s cliffbrake (Pellaea wrightiana), and little buckthorn (Condalia ericoides). And also a family of introduced aoudads with TWO adorable babies. I also got to see my first javelina (as roadkill) and all kinds of birds new to me.

Tree cholla ( Cholla  sp.)

Tree cholla (Cholla sp.)

Havard’s century plant ( Agave havardiana )

Havard’s century plant (Agave havardiana)

Wright’s cliffbrake ( Pellaea wrightiana )

Wright’s cliffbrake (Pellaea wrightiana)

Little buckthorn ( Condalia ericoides )

Little buckthorn (Condalia ericoides)

Aoudads in the distance.

Aoudads in the distance.

Finally I got to the coordinates - luckily google preloaded the directions on my phone because there was absolutely no cell service where I was. I parked and walked to the plants. And lo, I present to you, Quercus hinckleyi.

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It’s in the white oak family, which I guess means more than just “has round leaves.” These leaves look like holly, and even the shed ones on the ground still had some stabbiness left in them. It’s quite diminutive - certainly compared to any oak I’ve ever seen and even by shrub standards. I’d pinch its cheeks if that wouldn’t make my fingers bleed. After getting the pics I needed and doing the atheist’s version of saying a prayer over it, I floated back to my car like a cartoon cat in love.

The rest of the trip was great and I can’t wait to go back.

Since returning, I have shown several of my non-plant nerd friends the pics of hinckleyi and they seem politely impressed but not, like, actually impressed. This is totally understandable! If your experience with plants is on the order of what looks best in a planting or what tastes best in your tummy, this shrub is not for you. After all “it’s only value is as a curiosity.”

I don’t know about that. I feel like it’s value is greater than that for humans - it’s a window into the North American continent before the climate shifted 10,000 years ago, it’s an individual member of our vast botanical heritage, it is unique, it is adorbs, and it helped Dr. Ashley, and therefore us, understand more things about the movement of oak pollen.

But beyond what it does for US, what if, and hear me out, what if it has a right to existence on its own, without being displaced by pipelines or aoudads or poachers? It is a member of its ecological community, and just like I feel a loss when a member of my community passes, we don’t have the language to articulate what is felt when a member of an ecosystem winks out forever.

Janet Backs told me that she heard of someone who was trying to poach acorns from a subpopulation of hinckleyi and that the landowners where that shrub is actually chased those folks for miles and miles down the road. I love that. I wish every single threatened species/subpopulation had someone who understood its value beyond what it does for humans enough to chase people, possibly with a gun, for miles and miles.

I have had a paltry bucket list for most of my adult life - boring stuff like meeting my heroes or getting to a 7th bowl of never-ending-pasta. But despite their apparent lack of reverence for Q. hinckleyi I think a pretty good guiding list for me would be to visit each of the 77 oaks of North America in their native habitats. I know they won’t all be as special as this experience, but what better way to visit the corners of this continent and its myriad ecological communities, than by visiting each of its oaks? I currently can’t think of any, and would invite anyone to, if not fund me, join me.

An Iris With Multiple Parents

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The Abbeville iris (Iris nelsonii) is a very special plant. It is the rarest of the so-called “Louisiana Irises” and can only be found growing naturally in one small swamp in southern Louisiana. If you are lucky, you can catch it in flower during a few short weeks in spring. The blooms come in a range of colors from reddish-purple to nearly brown, an impressive sight to see siting atop tall, slender stems. However, the most incredible aspect of the biology of this species is its origin. The Abbeville iris is the result of hybridization between not two but three different iris species.

When I found out I would be heading to Louisiana in the spring of 2019, I made sure that seeing the Abbeville iris in person was near the top of my to-do list. How could a botany nut not want to see something so special? Iris nelsonii was only officially described as a species in 1966. Prior to that, many believed hybridization played a role in its origin. Multiple aspects of its anatomy appear intermediate between other native irises. It was not until proper molecular tests were done that the picture became clear.

The Abbeville iris genome contains bits and pieces of three other irises native to Louisiana. The most obvious parent was yet another red-flowering species - the copper iris (Iris fulva). It also contained DNA from the Dixie iris (Iris hexagona) and the zig-zag iris (Iris brevicaulis). If you had a similar childhood as I did, then you may have learned in grade school biology class that hybrids are usually biological dead ends. They may exhibit lots of beneficial traits but, like mules, they are often sterile. Certainly this is frequently the case, especially for hybrid animals, however, more and more we are finding that hybridization has resulted in multiple legitimate speciation events, especially in plants.

How exactly three species of iris managed to “come together” and produce a functional species like I. nelsonii is interesting to ponder. Its three parent species each prefers a different sort of habitat than the others. For instance, the copper iris is most often found in seasonally wet, shady bottomland hardwood forests as well as the occasional roadside ditch, whereas the Dixie iris is said to prefer more open habitats like wet prairies. In a few very specific locations, however, these types of habitats can be found within relatively short distances of eachother.

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Apparently at some point in the past, a few populations swapped pollen and the eventual result was a stable hybrid that would some day be named Iris nelsonii. As mentioned, this is a rare plant. Until it was introduced to other sites to ensure its ongoing existence in the wild, the Abbeville iris was only know to occur in any significant numbers at one single locality. This necessitates the question as to whether or not this “species” is truly unique in its ecology to warrant that status. It could very well be that that single locality just happens to produce a lot of one off hybrids.

In reality, the Abbeville iris does seem to “behave” differently from any of its parental stock. For starters, it seems to perform best in habitats that are intermediate of its parental species. This alone has managed to isolate it enough to keep the Abbeville from being reabsorbed genetically by subsequent back-crossing with its parents. Another mechanism of isolation has to do with its pollinators. The Abbeville iris is intermediate in its floral morphology as well, which means that pollen placement may not readily occur when pollinators visit different iris species in succession. Also, being largely red in coloration, the Abbeville iris receives a lot of attention from hummingbirds.

Although hummingbirds do not appear to show an initial preference when given the option to visit copper and Abbeville irises at a given location, research has found that once hummingbirds visit an Abbeville iris flower, they tend to stick to that species provided enough flowers are available. As such, the Abbeville iris likely gets the bulk of the attention from local hummingbirds while it is in bloom, ensuring that its pollen is being delivered to members of its own species and not any of its progenitors. For all intents and purposes, it would appear that this hybrid iris is behaving much like a true species.

As with any rare plant, its ongoing survival in the wild is always cause for concern. Certainly Louisiana is no stranger to habitat loss and an ever-increasing human population coupled with climate change are ongoing threats to the Abbeville iris. Changes in the natural hydrologic cycle of its swampy habitat appears to have already caused a shift in its distribution. Whereas it historically could be found in abundance in the interior of the swamp, reductions in water levels have seen it move out of the swamp and into ditches where water levels remain a bit more stable year round. Also, if its habitat were to become more fragmented, the reproductive barriers that have maintained this unique species may degrade to the point in which it is absorbed back into an unstable hybrid mix with one or a couple of its parent species. Luckily for the Abbeville, offspring have been planted into at least one other location, which helps to reduce the likelihood of extinction due to a single isolated event.


Photo Credit: [1]

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

The Succulent Passionflowers

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Succulent passionflowers?! It took me a minute to get my head wrapped around the idea. It wasn’t until I saw one in flower that I truly understood. The genus Adenia is found throughout east and west Africa, Southeast Asia, and hits its peak diversity in Madagascar. It comprises approximately 100 species and, as a whole, is poorly understood. Today I would like to introduce you to this bizarre genus within Passifloraceae.

Adenia glauca

Adenia glauca

Adenia is, to date, the second largest genus within the Passionflower family and yet delineating species has been something of a nightmare for botanists over the years. At least some of this confusion lies within the diversity of this odd group. It has been said that few angiosperm lineages surpass Adenia in the diversity of growth forms they exhibit. Though all could be considered succulent to some degree, Adenia runs the gamut from trees to vines, and even tuberous herbs.

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Even within individual species, the overall form of these plants can vary widely depending on the conditions under which they have been growing. Their succulent nature and that fact that many species can reach rather large proportions means that herbarium records for this group are scant at best. Many are only known from a single, incomplete collection of a few bits and pieces of plant. Also, juvenile plants often look very different from their adult forms, making timing of the collection crucial for proper analysis.

Adenia subsessilifolia

Adenia subsessilifolia

To complicate matters more, all Adenia are dioecious, meaning that individual plants are either male or female. Male and female flowers of individual species look pretty distinct and differ a bit from what we have come to expect out of the passionflower family. Often collections were made on only a single sex. This is further complicated by the fact that these plants often exhibit very short flowering seasons. Most come into bloom right before the onset of the rainy season and are entirely leafless at that point in time. Because of this, it has been extremely difficult to accurately match flowering collections to vegetative collections. As such, nearly 1/4 of all Adenia species are missing descriptions of either male or female flowers and their fruits.

Female flower of  Adenia reticulata

Female flower of Adenia reticulata

Male flowers of  Adenia digitata

Male flowers of Adenia digitata

Flowers of  Adenia firingalavensis

Flowers of Adenia firingalavensis

Fruits of  Adenia hondala

Fruits of Adenia hondala

Even genetic work has failed to clear up much of the mysteries that surround this group. Some studies suggest that Adenia is sister to all other genera within Passifloraceae whereas others have even suggested it to be nestled neatly within the genus Passiflora. The most recent work hints at a placement among the tribe Passifloreae. If this confuses you, you are certainly not alone. Until a more complete sampling effort is done on Adenia, I think it is safe to say that this genus will be holding onto its taxonomic mysteries for the foreseeable future.

Adenia globosa

Adenia globosa

All Adenia are perennial plants but how they manage this differs from species to species. Some put all of their energy into underground tubers, producing annual stems and leaves that die back each year. Others don’t produce any tubers and instead store all of their water and nutrients within thick stems. This has made at least a handful of species a hit with succulent growers around the world. It is always an interesting sight to see a giant caudiciform trunk or base with bunches of spindly stems spraying out from the top.

Leaves and fruit of  Adenia cissampeloides

Leaves and fruit of Adenia cissampeloides

Juvenile  Adenia glauca

Juvenile Adenia glauca

Adenia are also extremely toxic plants. The conditions under which these plants evolved are tough and it appears that this group doesn’t want to take any chances on losing any biomass to herbivores. The main class of compounds they produce are called lectins. These proteins cause myriad issues within animal bodies including rapid cell death, blood clotting, inhibition of protein synthesis, and a disruption of ribosome and DNA function. Needless to say, its in any critters best interest to avoid nibbling on any species of Adenia. Even handling and pruning of these plants merits caution.

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Whether you’re a botanist, taxonomist, gardener, or just curious about plant diversity, Adenia is a wonderful example of just how many unknowns are still out there. Regardless of their taxonomic status, these are fascinating species, each with a wonderful ecology and intriguing evolutionary history. These plants are hardy survivors and a great example of the lengths a genus can go to when presented with new opportunities. Undoubtedly many more species await description but the plants we currently know of are fascinating to say the least.

Adenia pechuelii

Adenia pechuelii

Photo Credits: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

Further Reading: [1] [2]

The Drought Alert System of Terrestrial Plants has an Underwater Origin

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For plants, the transition from water to land was a monumental achievement that changed our world forever. Such a transition was fraught with unique challenges, not the least of which being the ever present threat of desiccation. A new study now suggests that those early land plants already had the the tools to deal with drought and they have their aquatic algal ancestors to thank.

One of the keys to being able to survive drought is being able to detect it in the first place. Without some sort of signalling pathway, plants would not be able to close up stomata and channel vital water and nutrients to more important tissues and organs. As such, elucidating the origins and function of drought signalling pathways in plants has been of great interest to science.

One key set of pathways involved in plant drought response is collectively referred to as the “chloroplast retrograde signaling network.” I’m not even going to pretend that I understand how these pathways operate in any detail but there is one aspect of this network that is the key to this recent discovery. It involves the means by which drought and high-light conditions are sensed in one part of the plant and how that information is then communicated to the rest of the plant. When this signalling pathway is activated, the plant can then begin to produce enzymes that go on to activate defense strategies such as stomatal closure.

Chara braunii  - a modern day example of a streptophyte alga

Chara braunii - a modern day example of a streptophyte alga

The surprise came when researchers at the Australian National University, in collaboration with researchers at the University of Florida, decided to study the chloroplast retrograde signaling network in more detail. They were interested in the inner workings of this process in relation to stomata. Stomata are tiny pores on the leaves and stems of terrestrial plants that regulate the exchange of gases like CO2 and oxygen as well as water vapor. To add some controls to their experiment, the team added a few species of aquatic algae into the mix. Algae do not produce stomata and therefore they reasoned that no traces of chloroplast retrograde signaling network enzymes should be present.

This is not what happened. Instead, the team discovered that the enzymes in question also showed up in a group of algae known as the streptophytes. This was exciting because streptophyte algae hail from the lineage thought to be ancestral to all land plants. It appears that the tools necessary for terrestrial plants to survive drought were already in place before their ancestors ever left the water.

Why this is the case could have something to do with the streptophyte lifestyle. Today, these algae are known to tolerate very tough conditions. Though outright drought is rarely a threat for these aquatic algae, they nonetheless have to deal with scenarios that resemble drought such as high salinity. Streptophyte algae found growing in ephemeral pools must cope with ever increasing concentrations of salinity as the water around them evaporates. It is possible that this drought signalling pathway may have evolved as a response to hyper-saline conditions such as these. Regardless of what was going on during those early days of plant evolution, this research indicates that the ability for terrestrial plants to deal with drought evolved before their ancestors ever left the water.

The closer we look, the more we can appreciate that evolution of important traits isn’t always de novo. More often it appears that new innovations result from a retooling of of older genetic equipment. In the case of land plants, a signalling pathway that allowed their aquatic ancestors to deal with water loss was coopted later on by organs such as leaves and stems to deal with the stresses of life on land. As the old saying goes, “life uhhh… finds a way.”

Photo Credits: [1] [2]

Further Reading: [1] [2]

The Gravel Ghost

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Look closely or you might miss it. The gravel ghost (Atrichoseris platyphylla) is a master of disguise. At home in a small pocket of southwestern North America, this wonderful member of the aster family only puts on a show when rains offer the parched landscape a momentary reprieve.

The gravel ghost is the only member of the genus Atrichoseris. It is different enough from the rest of the chicory tribe (Cichorieae) to warrant its monotypic status. The gravel ghost is a winter annual meaning its seeds germinate at some point in the fall and the plant spends most of the winter putting on growth. As you can probably imagine, life in this corner of the world is pretty tough. Rain is sparse to non-existent and many plants teeter on the edge of desiccation. The fleshy, semi-succulent leaves of the gravel ghost likely store just enough water to offer some insurance against prolonged drought.

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As if drying up wasn’t enough for this plant, the desert’s compliment of hungry herbivores are constantly on the lookout for any plant remotely alive that can offer sustenance. All it takes is a few encounters with the gravel ghost to understand how this plant manages to avoid as much attention as possible. As its common name suggests, this species blends in with the surrounding soil to an extreme degree. From what I can gather, there appears to be a lot of variation in gravel ghost leaf color depending on where the population is growing.

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Some are mostly green whereas others take on a mottled grey hue. Still others seem to have settled on a mixture of browns. It seems that no matter the substrate, the gravel ghost will do its best to blend in. Personally, I would love to see someone investigate what kind of genetic or environmental controls dictate leaf color in this species. It is fascinating to think about how plants can disguise themselves against herbivores.

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Starting in late winter and early spring, the gravel ghost needs to complete its annual life cycle. When rains punctuate the drought, the gravel ghost sends up a spindly inflorescence tipped with a few flower heads. If they are lucky, some stalks will avoid being nipped off by sheep and rabbits. Those that do put on quite a floral display. Each head or ‘capitulum’ explodes with clusters of bright white ray flowers. Only at this point does its affinity with the chicory tribe become apparent.

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The need for such a high impact floral display has everything to do with being an annual. There is only limited time for pollination and seed set. Each gravel ghost must produce enough seeds to enure that at least some survive. They simply don’t have multiple seasons to reproduction. Luckily its a member of the aster family and the opportunity for seed production is usually relatively high. With any luck, plenty of pollinators will find these plants tucked in among rocks and gravel and the process will begin again come that fall.

Photo Credit: Joey (www.instagram.com/crime_pays_but_botany_doesnt)

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



A Hardy Tillandsia That Deserves Our Respect

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As epiphytes go, Tillandsia recuvata (a.k.a. ball moss) doesn’t have the best reputation. All too often it is seen as an unsightly pest of trees that needs to be removed. This could not be farther from the truth. This hardy air plant does no harm to the trees on which it grows. What’s more, its relationship with a specific group of bacteria means it is a major contributor to soil fertility. Today I would like to sing the praise of the indefatigable Tillandsia recuvata.

Tillandsia recuvata is native throughout an impressive chunk of the Americas, from the southern United States through to northern Argentina and Chile. Wherever temperatures rarely dip below freezing, T. recurvata can make an easy living. One of the most remarkable aspects of this species is the array of habitat types in which it grows. This hardy little air plant is equally at home in sub-tropical conditions as it is arid desert habitats. Its ability to tolerate heat, drought, and plenty of air pollution has led to its colonization of urban environments as well.

One of the keys to its success is the way in which T. recuvata handles photosynthesis. As is typical of the bromeliad family (Bromeliaceae), T. recuvata utilizes CAM photosynthesis. Instead of opening its stomata during the day, when high temperatures and baking sun would lead to unsustainable rates of water loss, T. recurvata opens its stomata at night, taking in CO2 while temperatures are more favorable. It then stores this CO2 as an organic acid that it can use later on the next day when the sun comes up. In doing so, T. recurvata can keep its stomata closed and save on water while still being able to synthesize the carbohydrates it needs.

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I think one of the main reasons T. recurvata doesn’t get the respect that many of its cousins receive is that it doesn’t put on a spectacular floral show when in bloom. Tiny purple to lavender petals just barely emerge from between bracts located a the tips of long flowers stalks. The flowers don’t last long and are quickly replaced by long, brown seed capsules. These capsules eventually burst open, releasing plenty of tiny seeds, each adorned with wispy filaments that help them take advantage of the slightest breeze. Though the seeds themselves are small and don’t show many adaptations for adhering to suitable substrates, I have found that those silky filaments tend to get matted up and stuck on whatever surface they land on. In this way, seeds at least have a chance to germinate on everything from twigs to power lines, and even other Tillandsias.

The reason this species earned the specific epithet ‘recurvata’ and the common name ‘ball moss’ has to do with both its growth habit and its propensity to grow on others of its own kind. Each leaf curls backward as it grows, giving individual plants a spherical shape. As more and more seedlings germinate on and around one another, these colonies can take on a massive, ball-like appearance. This has led many to classify this species as a parasite, however, this is not the case at all. It is wrongly assumed that these plants weaken the trees on which they grow and this is simply not the case.

Like many other epiphytes, T. recurvata likes a lot of sunlight. As such, plants tend to do better a the tops of trees or near the tips of branches. Certainly this can cause some degree of shading for the trees on which they grow, but this is insignificant considering how much a tree’s own branches and leaves shade those further down on the trunk. Also, T. recurvata are quick to move in on branches that have lost foliage or are already dead. This can often appear are is the plants have taken over the tree, causing it to die back. In reality, T. recurvata colonies are a merely a symptom of a tree already stressed by other factors. As the canopy starts to thin, more air plants are able to find suitable habitat for germination and growth. Trees covered in T. recurvata were already weak or dying, not the other way around.

In fact, evidence is showing that T. recurvata are actually an important source of nitrogen for the surrounding environment. Within their tissues, T. recurvata house specialized bacteria in the genus Pseudomonas, which are capable of fixing nitrogen directly from the atmosphere. In return for a place to live, these bacteria provide their air plant host with a nitrogen boost that would otherwise be unavailable. When T. recurvata detach from whatever they are growing on (something they frequently do in droves), they fall to the ground, rot, and enrich the soil with a shot of nitrogen. As such, these wonderful epiphytes are actually a boost to the growth of not only their hosts but many other plant species as well.

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Probably the most incredible feat of this species has been its conquest of the human environment. Throughout its range you can find T. recurvata thriving on man-made structures like power lines. For a species that gets all of its needs from the atmosphere, it is amazing how well T. recurvata is able to handle air pollution. Because it is so darn hardy, this air plant has caught the attention of more than one researcher. In fact, some are even looking at T. recurvata as a unique candidate for green roof construction in warmer climates.

All in all, this is one of the hardiest plants you are going to encounter in the Americas. One should look on at T. recurvata colonies with respect and admiration, not disgust and disdain. We fight species like this for all of the wrong reasons when in reality, we should be embracing them as both survivors and important components of ecosystem health. I hope this post has been able to do away with at least some of the misconceptions about this species. Three cheers for Tillandsia recurvata!

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

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

The Floating Bladderwort

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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.

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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.

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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: www.sarracenia.com, Dr. Mark Whitten, [3] [4]

Further Reading: [1] [2]

The Creeping Fuchsia

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Meet Fuchsia procumbens aka the creeping Fuchsia. This lovely plant is endemic to New Zealand where, sadly, it is threatened. In its native habitat, it is strictly a coastal species, prefering to grow in sandy soils. The  flowers are quite unlike most other members of the genus Fuchshia and they exhibit an interesting flowering strategy. 

Fuchsia procumbens produces 3 distinct flower forms, flowers with only  working male parts, flowers with only working female parts, and hermaphroditic flowers. One reason for this is to avoid self-pollination. The other reason may have something to do with energy costs. When growing conditions are less than stellar, the plant saves energy by producing male flowers. 

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Pollen is relatively cheap after all. When conditions improve, the plant may allocate more resources to female and hermaphroditic flowers. This strategy worries some botanists because it seems like some populations of F. procumbens only ever produce single sex flowers. After pollination, the flowers give way to bright red berries that are larger than the flowers themselves!

The most interesting thing about this species is, despite its apparent specificity in habitat preferences in the wild, it competes well with aggressive grasses, which has made it a very popular ground cover. As it turns out, its growing popularity in the garden trade may save this species from being placed on the endangered species list.

Photo Credits: [1] [2]

Further Reading: [1] [2]