Let's Talk About Recruitment

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For any species to be considered successful, it must replace itself generation after generation. We call this process recruitment and it is very important. After all, reproduction is arguably the most fundamental aspect of life in a Darwinian sense. For plants, this can be done either vegetatively or sexually via seeds and spores. Though vegetative reproduction is a fundamental process for many plants around the globe, seed or spore germination is arguably the most important. To truly understand what a plant needs, we have to understand its germination requirements.

Recruitment is a considerable limiting factor for plant populations. In fact, it is the first major bottleneck plants must pass through. It is estimated that a majority of plant mortality occurs during the germination and seedling stages. However, not all plants are equal in this way. Some plants are considered seed or propagule limited whereas others are habitat limited.

If a plant is seed limited, it means that its ability to expand its population or colonize new habitats its limited by the ability of seeds (or spores) to make it to a new location. Once there, nature takes its course and germination occurs with little impediment. If a plant is habitat limited, however, things get a bit more tricky. For habitat limited plants, simply getting seeds to a new location is not enough. Some other aspect of the environment (soil moisture, texture, temperature, disturbance, etc.) limit successful germination. Only when the right conditions are present can habitat limited plants germinate and begin to grow.

Habitat limitation is probably the most common limit to plant establishment. Simply put, not all plants will be successful everywhere. Even the successful growth and persistence of adult plants can be poor predictors of seedling success. Many plants can live for decades or even centuries and the conditions that were present when they germinated may have long since changed. Even the presence of the adults themselves can make a site unsuitable for germination. Think of all of those fire adapted species out there that require the entire community to burn before their seeds will ever germinate.

In reality, it is likely that most plants are habitat limited to some degree. These are not binary categories after all, rather they are aligned along a spectrum of possibilities. The fact that most plants don’t completely take over an area once seeds or spores arrive is proof of the myriad limits to plant establishment. As such, recruitment limitation is extremely important to study. It can make a huge difference in the context of conservation and restoration. Even the successful establishment of adult plants is no guarantee that seedlings stand a chance. Without successful recruitment, all you have left is a nice garden that is doomed to run its course. By understanding the limits to plant recruitment, we can do much more than just improve on our ability to protect and bolster plant populations, we can also gain insights into why so many plants remain rare on the landscape and so few ever rise to dominance.

Photo Credits: [1]

Further Reading: [1] [2]

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]




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 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]

Maxipiñon: One of the Rarest Pines in the World

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The maxipiñon (Pinus maximartinezii) is one of the rarest pines on Earth. A native of southern Sierra Madre Occidental, Mexico, nearly all individuals of this species can be found scattered over an area that collectively spans only about 3 to 6 square miles (5 – 10 km²) in size. Needless to say, the maxipiñon teeters on the brink of extinction. As a result, a lot of effort has been put forward to better understand this species and to develop plans aimed at ensuring it is not lost forever.

The maxipiñon has only been known to science for a few decades. It was described back in 1964 after botanist Jerzy Rzedowski noted some exceptionally large pine seeds for sale at a local market. He named the species in honor of Maximino Martínez, who contributed greatly to our understanding of Mexican conifers. However, it was very obvious that the maxipiñon was well known among the residents of Zacatecas.

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The reason for this are its seeds. The maxipiñon is said to produce the largest and most nutritious seeds of all the pines. As such, it is a staple of the regional diet. Conversations with local farmers suggest that it was much more common as recent as 60 years ago. Since then, its numbers have been greatly reduced. It soon became apparent that in order to save this species, we had to learn a lot more about what threatens its survival.

The most obvious place to start was recruitment. If any species is to survive, reproduction must outpace death. A survey of local markets revealed that a lot of maxipiñon seeds were being harvest from the wild. This would be fine if maxipiñon were widespread but this is not the case. Over-harvesting of seeds could spell disaster for a species with such small population sizes.

Indeed, surveys of wild maxipiñon revealed there to be only 2,000 to 2,500 mature individuals and almost no seedlings. However, mature trees do produce a considerable amount of cones. Therefore, the conclusion was made that seed harvesting may be the single largest threat to this tree. Subsequent research has suggested that seed harvests actually may not be the cause of its rarity. It turns out, maxipiñon population growth appears to be rather insensitive to the number of seeds produced each year. Instead, juvenile tree survival seems to form the biggest bottleneck to population growth.

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You see, this tree appears to be more limited by suitable germination sites than it does seed numbers. It doesn’t matter if thousands of seeds are produced if very few of them ever find a good spot to grow. Because of this, scientists feel that there are other more serious threats to the maxipiñon than seed harvesting. However, humans are still not off the hook. Other human activities proved to be far more damaging.

About 50 years ago, big changes were made to local farming practices. More and more land was being cleared for cattle grazing. Much of that clearing was done by purposefully setting fires. The bark of the maxipiñon is very thin, which makes it highly susceptible to fire. As fires burn through its habitat, many trees are killed. Those that survive must then contend with relentless overgrazing by cattle. If that wasn’t enough, the cleared land also becomes highly eroded, thus further reducing its suitability for maxipiñon regeneration. Taken together, these are the biggest threats to the ongoing survival of this pine. Its highly fragmented habitat no longer offers suitable sites for seedling growth and survival.

As with any species this rare, issues of genetic diversity also come into play. Though molecular analyses have shown that maxipiñon does not currently suffer from inbreeding, it has revealed some interesting data that give us hints into the deeper history of this species. Written in maxipiñon DNA is evidence of an extreme population bottleneck that occurred somewhere between 400 and 1000 years ago. It appears that this is not the first time this tree has undergone population decline.

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There are a few ways in which these data can be interpreted. One is that the maxipiñon evolved relatively recently from a small number of unique and isolated individuals. Perhaps a hybridization event occurred between two closely related piñon species - the weeping piñon (Pinus pinceana) and Nelson piñon (Pinus nelsonii). Another possibility, which does not rule out hybridization, is that the maxipiñon may actually be the result of artificial selection by agriculturists of the region. Considering the value of its seeds today, it is not hard to imagine farmers selecting and breeding piñon for larger seeds. It goes without saying that these claims are largely unsubstantiated and would require much more evidence to say with any certainty, however, there is plenty of evidence that civilizations like the Mayans were conserving and propagation useful tree species much earlier than this.

Despite all we have learned about the maxipiñon over the last few decades, the fate of this tree is far from secure. Ex situ conservation efforts are well underway and you can now see maxipiñon specimens growing in arboreta and botanical gardens around the world. Seeds from these populations are being used for storage and to propagate more trees. Sadly, until something is done to protect the habitat on which it relies, there is no telling how long this species will last in the wild. This is why habitat conservation efforts are so important. Please support local land conservation efforts in your area because the maxipiñon is but one species facing the loss of its habitat.

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

Further Reading [1] [2] [3]

The Largest Mistletoe

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When we think of mistletoes, we generally think about those epiphytic parasites living on branches way up in the canopy. The mistletoe we are discussing in this post, however, is a decent sized tree. Nuytsia floribunda is a native of western Australia where it is known locally as moojar or the Christmas tree. To the best of our knowledge, it is the largest mistletoe known to science.

Nuytsia floribunda is a member of the so-called showy mistletoe family (Loranthaceae). It along with all of its mistletoe cousins reside in the order Santalales but from a phylogenetic standpoint, the family Loranthaceae is considered sister to all other mistletoes. This has excited my botanists as it allows us a chance to better understand how parasitism may have evolved in this group as a whole.

Speaking of parasitism, there are some incredible things going on with N. floribunda that are worth talking about. For starters, it is not fully parasitic but rather hemiparasitic. As you can tell by looking at the tree decked out in a full canopy of leaves, N. floribunda is entirely capable of photosynthesizing on its own. In fact, experts feel that it is fully capable of meeting all of its own carbohydrate needs. Instead, it parasitizes other plants in order to acquire water and minerals. How it manages this is remarkable to say the least.

Nuytsia floribunda is a root parasite. Its own roots fan out into the surrounding soil looking for other roots to parasitize. Amazingly, exploratory roots of individual N. floribunda have been found upwards of 110 meters (360 ft.) or more away from the tree. When N. floribunda do find a suitable host root, something incredible happens. It begins to form specialized roots called “haustoria”, which to form a collar-like structure around the host’s roots.

Whole haustoria of Nuytsia (white [ha]) and host root (dark brown). * indicates `gland' and developing `cutting device.

Whole haustoria of Nuytsia (white [ha]) and host root (dark brown). * indicates `gland' and developing `cutting device.

The collar gradually swells and a small horn forms on the inside of the haustoria. Swelling of the haustoria is the result of an influx of water and as the pressure around the host root builds, the haustorial horn of N. floribunda physically cuts into its victim. Once this cut is formed, the haustoria form balloon-like outgrowths which intrude into the xylem tissues of the host root, thus forming the connection that allows N. floribunda to start stealing the water and minerals it needs.

Even more amazing is the fact that roots aren’t the only thing that N. floribunda will attempt to exploit. Many inanimate objects have been found wrapped up in a haustorial embrace including dead twigs, rocks, fertilizer granuals, and even electric cables! Its non-selective parasitic nature appears to have left it open to exploring other, albeit dead end options. I don’t want to paint the picture that this tree as the enemy of surrounding vegetation. It is worth noting that N. floribunda extracts very little from any given host so its impact is spread out among the surrounding vegetation, making its overall impact on host plants minimal most of the time.

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Provided its needs have been met, N. floribunda puts on one heck of a show around December. In fact, the timing of its blooms is the reason it earned the common name of Christmas tree. Flowering for this species is not a modest affair. Each tree is capable of producing multiple meter-long inflorescences decked out in sprays of bright orange to yellow flowers. The flowers themselves produce copious amounts of pollen and nectar, making it an important food source for resident pollinators. Though many different species have been documented visiting the flowers, it is thought that beetles and wasps are the most effective at pollination.

Seed dispersal for N. floribunda is mainly via wind. Each fruit is adorned with three prominent wings. After they detach from the tree, the fruits usually break apart into three samaras, each with its own wing. The key for success of any propagule is ending up in a site suitable for germination. According to some, this can be a bit tricky and attempts at cultivating this plant in captivity have not been terribly successful. It would seem that nature knows best when it comes to reproductive success in N. floribunda. It may be worth trying to figure it out though because recent evidence suggests that this species is not faring well with human development. As the surrounding landscapes of western Australia become more and more urbanized, plants like N. floribunda seem to be on the decline. Perhaps renewed interest in growing this species could change the tide for it as well as others.

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

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

The Creeping Strawberry Pine

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With its small, creeping habit and bright red, fleshy female cones, it is easy to see how Microcachrys tetragona earned its common name “creeping strawberry pine.” This miniature conifer is as adorable as it is interesting. With a fossil history that spans 66 million years of Earth’s history, it also has a lot to teach us about biogeography.

Today, the creeping strawberry pine can only be found growing naturally in western Tasmania. It is an alpine species, growing best in what is commonly referred to as alpine dwarf scrubland, above 1000 m (3280 ft) in elevation. Like the rest of the plants in such habitats, the creeping strawberry pine does not grow very tall at all. Instead, it creeps along the ground with its prostrate branches that barely extend more than 30 cm (0.9 ft) above the soil. This, of course, is likely an adaptation to its alpine environment. Plants that grow too tall frequently get knocked back by brutal winds and freezing temperatures among other things.

The typical growth habit of the creeping strawberry pine.

The typical growth habit of the creeping strawberry pine.

The creeping strawberry pine is not a member of the pine family (Pinaceae) but rather the podocarp family (Podocarpaceae). This family is interesting for a lot of reasons but one of the coolest is the fact that they are charismatic representatives of the so-called Antarctic flora. Along with a handful of other plant lineages, it is thought that Podocarpaceae arose during a time when most of the southern continents were combined into a supercontinent called Gondwana. Subsequent tectonic drift has seen the surviving members of this flora largely divided among the continents of the Southern Hemisphere. By combining current day distributions with fossil evidence, researchers are able to use families such as Podocarpaceae to tell a clearer picture of the history of life on Earth.

What is remarkable is that among the various podocarps, the genus Microcachrys produces pollen with a unique morphology. When researchers look at pollen under the microscope, whether extant or fossilized, they can say with certainty if it belongs to a Microcachrys or not. The picture we get from fossil evidence paints an interesting picture for Microcachrys diversity compared to what we see today. It turns out, Microcachrys endemic status is a more recent occurrence.

This distinctive, small, trisaccate pollen grain is typical of what you find with  Microcachrys  whereas all other podocarps produce bisaccate pollen.

This distinctive, small, trisaccate pollen grain is typical of what you find with Microcachrys whereas all other podocarps produce bisaccate pollen.

The creeping strawberry pine is what we call a peloendemic, meaning it belongs to a lineage that was once far more widespread but today exists in a relatively small geographic location. Fossilized pollen from Microcachrys has been found across the Southern Hemisphere, from South America, India, southern Africa, and even Antarctica. It would appear that as the continents continued to separate and environmental conditions changed, the mountains of Tasmania offered a final refuge for the sole remaining species in this lineage.

Another reason this tiny conifer is so charming are its fruit-like female cones. As they mature, the scales around the cone swell and become fleshy. Over time, they start to resemble a strawberry more than anything a gymnosperm would produce. This is yet another case of convergent evolution on a seed dispersal mechanism among a gymnosperm lineage. Birds are thought to be the main seed dispersers of the creeping strawberry pine and those bright red cones certainly have what it takes to catch the eye of a hungry bird. It must be working well for it too. Despite how narrow its range is from a global perspective, the creeping strawberry pine is said to be locally abundant and does not face the same conservation issues that many other members of its family currently face. Also, its unique appearance has made it something of a horticultural curiosity, especially among those who like to dabble in rock gardening.

Mature female cones look more like angiosperm fruit than a conifer cone.

Mature female cones look more like angiosperm fruit than a conifer cone.

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

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

Meet the She-Oaks

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No, what you are looking at here is not a type of conifer. Nor is it an oak. This odd plant belongs in its own family - Casuarinaceae. Despite their gymnosperm appearance, this is in fact a family of flowering plants. Though the name “she-oak” does hint at their larger position within the order Fagales, it was actually given to these trees in reference to the density of their wood in comparison to more commonly harvested oak species. Other common names for trees in this group include ironwood, bull-oak, beefwood.

As a whole this family sorts out as sister to Myricaceae in the order Fagales. It' is comprised of 4 genera (Allocasuarina, Casuarina, Ceuthostoma, and Gymnostoma) and roughly 91 species spread among Australia, Malaysia, and much of Polynesia. It is extremely difficult to make generalizations across so many species but there is one aspect of this family that makes them stand out - their appearance.

Gymnostoma  sp.

Gymnostoma sp.

Gymnostoma nobile  in Sarawak, Malaysia.

Gymnostoma nobile in Sarawak, Malaysia.

Without close inspection, one could be forgiven for thinking the various Casuarinaceae were species of conifer. For starters, their leaves have been reduced to tiny whorls surrounding their photosynthetic stems. The stems themselves have taken up the role of photosynthetic organs, which is one of the reasons this family is known for its drought tolerance. Reducing the surface area available for gas exchange helps to reduce water loss in the process. The stems themselves are arranged with whorls around the branches, giving them a rather bunched appearance. The photosynthetic branches are sometimes referred to as being ‘equisetiform’ as they superficially resemble the stems of Equisetum. They do not shed their photosynthetic branches and are therefore evergreen.

As mentioned, these are flowering plants. Their flowers themselves are aggregated into spike-like inflorescences near the tips of branches. Clusters of male flowers resemble catkin-like strobili and are often brightly colored. Female flowers are clustered into a more ovoid shape, with long, filamentous pistils sticking out like fiery, red pompoms. After fertilization, bracts at the base of the female flowers swell and the whole inflorescence starts to look more like some sort of a conifer cone than anything floral. This may have to do with the fact that, like conifers, the various Casuarinaceae are wind pollinated. Therefore, their reproductive structures have had to deal with similar selective forces related to optimizing pollen dispersal and capture.

Casuarina equisetifolia  with catkin-like male flowers and smaller, red female flowers.

Casuarina equisetifolia with catkin-like male flowers and smaller, red female flowers.

Allocasuarina distyla  female flowers and infructescence.

Allocasuarina distyla female flowers and infructescence.

Another interesting trait common to Casuarinaceae is the ability to fix nitrogen. The plants themselves don’t do the fixing, rather they form specialized nodules on their roots that house nitrogen-fixing bacteria. Unlike perennial legumes that regrow their nodules year after year, the members of Casuarinaceae hold onto their nodules, which can grow into impressive structures over time. This ability to house nitrogen-fixing bacteria is also shared with other members of the order Fagales, including members of Betulaceae and Myricaceae.

Thanks to the fact that they can tolerate drought, fix nitrogen, and have high timber value, species of Casuarinaceae have been introduced far outside of their native ranges. This has created yet another invasive species issue. Various Casuarinaceae have become serious pests in places like Central and South America, the Carribbean, and the Middle East. Control of such hardy plants can be extremely difficult once they reach a critical mass that maintains them on the landscape. Keep you eye out for these species. Not only are they interesting in their own right, knowing them can help you better understand their role in ecosystems both native and not.

Allocasuarina decaisneana  (Desert Oaks), Central Australia

Allocasuarina decaisneana (Desert Oaks), Central Australia

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

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

Crab Spiders and Pitcher Plants: A Dynamic Duo

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

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

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

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

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

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

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

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

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

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

The Japanese Umbrella Pine

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My first impression of the Japanese umbrella pine was that I was looking at a species of yew (Taxus spp.). Sure, its features were a bit more exaggerated than I was used to but what do I know? Trying to understand tree diversity is a recent development in my botanical obsession so I don’t have much to base my opinions on. Regardless, I am glad I gave the little sapling I was looking at a closer inspection. Turns out, the Japanese umbrella pine is most definitely not a yew. It is actually unique in its taxonomic position as the only member of the family Sciadopityaceae.

The Japanese umbrella pine goes by the scientific name of Sciadopitys verticillata. Both common and scientific names hint at the whorled arrangements of its “leaves.” I place leaves in quotes because they are not leaves at all. One of the most remarkable features of this tree is the fact that those whorled leaves are actually thickened, photosynthetic extensions of the stem known as “cladodes.”

Those tiny bumps along the stems are actually highly reduced leaves whereas the whorls of photosynthetic “leaves” are actually modified extensions of the stem called “cladodes.”

Those tiny bumps along the stems are actually highly reduced leaves whereas the whorls of photosynthetic “leaves” are actually modified extensions of the stem called “cladodes.”

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It seems that the true leaves of the Japanese umbrella pine have, through evolutionary time, been reduced to tiny, brown scales that clasp the stems. I am not sure what evolutionary advantage(s) cladodes infer over leaves, however, at least one source suggested that cladodes may have fewer stomata and therefore can help to reduce water loss. Until someone looks deeper into this mystery, we cannot say for sure.

As a tree, the Japanese umbrella pine is slow growing. Records show that young trees can take upwards of a decade to reach average human height. However, given time, the Japanese umbrella pine can grow into an impressive specimen. In the forests of Japan, it is possible to come across trees that are 65 to 100 ft (20 – 35 m) tall. It was once wide spread throughout much of southern Japan, however, an ever-increasing human population has seen that range reduced.

A 49.5 million years old fossil of a  Sciadopitys  cladode.

A 49.5 million years old fossil of a Sciadopitys cladode.

The gradual reduction of this species is not solely the fault of humans. Fossil evidence shows that the genus Sciadopitys was once wide spread throughout parts of Europe and Asia as well. Whereas the current diversity of this genus is limited to a single species, fossils of at least three extinct species have been found in rocks dating back to the Triassic Period, some 230 million years ago. It would appear that this obscure conifer family, like so many other gymnosperm lineages, has been on the decline for quite some time.

Despite the obscure strangeness of the Japanese umbrella tree, it has gained considerable popularity as a unique landscape tree. Because it hails from a relatively cool regions of Japan, the Japanese umbrella tree adapts quite well to temperate climates around the globe. Enough people have grown this tree that some cultivars even exist. Whether you see it as a specimen in an arboretum or growing in the wild, know that you are looking at something quite special. The Japanese umbrella tree is a throwback to the days when gymnosperms were the dominant plants on the landscape and we are extremely lucky that it made it through to our time.

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

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

Resurrecting Café Marron

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Back in 1980, a school teacher on the island of Rodrigues sent his students out to look for plants. One of the students brought back a cutting of a shrub that astounded the botanical community. Ramosmania rodriguesii, more commonly known as café marron, was up until that point only known from one botanical description dating back to the 1800's. The shrub, which is a member of the coffee family, was thought to have been extinct due to pressures brought about during the colonization of the island (goats, invasive species, etc.). What the boy brought back was indeed a specimen of café marron but the individual he found turned out to be the only remaining plant on the island.

News of the plant quickly spread. It started to attract a lot of attention, not all of which was good. There is a belief among the locals that the plant is an herbal remedy for hangovers and venereal disease (hence its common name translates to ‘brown coffee’) and because of that, poaching was rampant. Branches and leaves were being hauled off at a rate that was sure to kill this single individual. It was so bad that multiple layers of fencing had to be erected to keep people away. It was clear that more was needed to save this shrub from certain extinction.

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Cuttings were taken and sent to Kew. After some trial and tribulation, a few of the cuttings successfully rooted. The clones grew and flourished. They even flowered on a regular basis. For a moment it looked like this plant had a chance. Unfortunately, café marron did not seem to want to self-pollinate. It was looking like this species was going to remain a so-called “living dead” representative of a species no longer able to live in the wild. That is until Carlos Magdalena (the man who saved the rarest water lily from extinction) got his hands on the plants.

The key to saving café marron was to somehow bypass its anti-selfing mechanism. Because so little was known about its biology, there was a lot of mystery surrounding its breeding mechanism. Though plenty of flowers were produced, it would appear that the only thing working on the plant were its anthers. They could get viable pollen but none of the stigmas appeared to be receptive. Could it be that the last remaining individual (and all of its subsequent clones) were males?

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This is where a little creativity and a lot of experience paid off. During some experiments with the flowers, it was discovered that by amputating the top of the stigma and placing pollen directly onto the wound one could coax fertilization ans fruiting. From that initial fruit, seven seeds were produced. These seeds were quickly sent to the propagation lab but unfortunately the seedlings were never able to establish. Still, this was the first indication that there was some hope left for the café marron.

After subsequent attempts at the stigma amputation method ended in failure, it was decided that perhaps something about the growing conditions of the first plant were the missing piece of this puzzle. Indeed, by repeating the same conditions the first individual was exposed to, Carlos and his team were able to coax some changes out of the flowering efforts of some clones. Plants growing in warmer conditions started to produce flowers of a slightly different morphology towards the end of the blooming cycle. After nearly 300 attempts at pollinating these flowers, a handful of fruits were formed!

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From these fruits, over 100 viable seeds were produced. What’s more, these seeds germinated and the seedlings successfully established. Even more exciting, the seedlings were a healthy mix of both male and female plants. Carlos and his team learned a lot about the biology of this species in the process. Thanks to their dedicated work, we now know that café marron is protandrous meaning its male flowers are produced before female flowers.

However, the story doesn’t end here. Something surprising happened as the seedlings continued to grow. The resulting offspring looked nothing like the adult plant. Whereas the adult plant has round, green leaves, the juveniles were brownish and lance shaped. This was quite a puzzle but not entirely surprising because the immature stage of this shrub was not known to science. Amazingly, as the plants matured they eventually morphed into the adult form. It would appear that there is more to the mystery of this species than botanists ever realized. The question remained, why go through such drastically different life stages?

A young café marron showing its brown, mottled, lance-shaped leaves.

A young café marron showing its brown, mottled, lance-shaped leaves.

The answer has to do with café marron's natural predator, a species of giant tortoise. The tortoises are attracted to the bright green leaves of the adult plant. By growing dull, brown, skinny leaves while it is still at convenient grazing height, the plant makes itself almost invisible to the tortoise. It is not until the plant is out of the range of this armoured herbivore that it morphs into its adult form. Essentially the young plants camouflage themselves from the most prominent herbivore on the island.

Thanks to the efforts of Carlos and his team at Kew, over 1000 seeds have been produced and half of those seeds were sent back to Rodrigues to be used in restoration efforts. As of 2010, 300 of those seed have been germinated, opening up many more opportunities for reintroduction into the wild. Those early trials will set the stage for more restoration efforts in the future. It is rare that we see such an amazing success story when it comes to such an endangered species. We must celebrate these efforts because they remind us to keep trying even if all hope seems to be lost. My hat is off to Carlos and the dedicated team of plant conservationists and growers at Kew.

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

Further Reading: [1] [2]

Meet the Pygmy Clubmoss

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No, these are not some sort of grass or rush. What you are looking at here is actually a member of the clubmoss family (Lycopodiaceae). Colloquially known as the pygmy clubmoss, this odd little plant is the only species in its genus - Phylloglossum drummondii. Despite its peculiar nature, very little is known about it.

The pygmy clubmoss is native to parts of Australia, Tasmania, and New Zealand but common it is not. From what I can gather, it grows in scattered coastal and lowland sites where regular fires clear the ground of competing vegetation. It is a perennial plant that makes its appearance around July and reaches reproductive size around August through to October.

Reproduction for the pygmy clubmoss is what you would expect from this family. In dividual plants will produce a reproductive stem that is tipped with a cone-like structure. This cone houses the spores, which are dispersed by wind. If a spore lands in a suitable spot, it germinates into a tiny gametophyte. As you can probably imagine, the gametophyte is small and hard to locate. As such, little is known about this part of its life cycle. Like all gametophytes, the end goal of this stage is sexual reproduction. Sperm are released and with any luck will find a female gametophyte and fertilize the ovules within. From the fertilized ovule emerges the sporophytes we see pictured above.

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As dormancy approaches, this strange clubmoss retreats underground where it persists as a tiny tuber-like stem. Though it is rather obscure no matter who you ask, there has been some scientific attention paid to this odd little plant, especially as it relates to its position on the tree of life. Since it was first described, its taxonomic affinity has moved around a bit. Early debates seemed to center around whether it belonged in Lycopodiaceae or its own family, Phylloglossaceae.

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Recent molecular work put this to rest showing that genetically the pygmy clubmoss is most closely related to another genus of clubmoss - Huperzia. This was bolstered by the fact that it shares a lot of features with this group such as spore morphology, phytochemistry, and chromosome number. The biggest difference between these two genera is the development of the pygmy clubmoss tuber, which is unique to this species. However, even this seems to have its roots in Lycopodiaceae.

If you look closely at the development of some lycopods, it becomes apparent that the pygmy clubmoss most closely resembles an early stage of development called the “protocorm.” Protocorms are a tuberous mass of cells that is the embryonic form of clubmosses (as well as orchids). Essentially, the pygmy clubmoss is so similar to the protocorm of some lycopods that some experts actually think of it as a permanent protocorm capable of sexual reproduction. Quite amazing if you ask me.

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Sadly, because of its obscurity, many feel this plant may be approaching endangered status. There have been notable declines in population size throughout its range thanks to things like conversion of its habitat to farmland, over-collection for both novelty and scientific purposes, and sequestration of life-giving fires. As mentioned, the pygmy clubmoss needs fire. Without it, natural vegetative succession quickly crowds out these delicate little plants. Hopefully more attention coupled with better land management can save this odd clubmoss from going the way of its Carboniferous relatives.

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

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

On the Flora of Antarctica

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Antarctica - the frozen continent. It is hard to think of a place on Earth that is less hospitable to life. Yet life does exist here and some of it is botanical. Though few in number, Anarctica’s diminutive flora is able to eke out an existence wherever the right conditions present themselves. It goes without saying that these plants are some of the hardiest around.

It is strange to think of Antarctica as having any flora at all. How many descriptions of plant families and genera say something to the effect of “found on nearly every continent except for Antarctica.” It didn’t always used to be this way though. Antarctica was once home to a diverse floral assemblage that rivaled anything we see in the tropics today. Millions upon millions of years of continental drift has seen this once lush landmass positioned squarely at Earth’s southern pole.

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Situated that far south, Antarctica has long since become a frozen wasteland of sorts. The landscape is essentially a desert. Instead of no precipitation, however, most water in this neck of the woods is completely locked up in ice for most of the year. This is one reason why plants have had such a hard time making a living here. That is not to say that some plants haven’t made it. In fact, a handful of species thrive under these conditions.

When anyone goes looking for plants in Antarctica, they must do so wherever conditions ease up enough for part of the year to allow terrestrial life to exist. In the case of this frozen continent, this means hanging out along the coast or one of handful of islands situated just off of the mainland. Here, enough land thaws during the brief summer months to allow a few plant species to take root and grow.

Antarctic hair grass ( Deschamsia antarctica )

Antarctic hair grass (Deschamsia antarctica)

The flora of Antarctica proper consists of 2 flowering plant species, about 100 species of mosses, and roughly 30 species of liverwort. The largest of these are the flowering plants - a grass known as Antarctic hair grass (Deschamsia antarctica), and member of the pink family with a cushion-like growth habit called Antarctic pearlwort (Colobanthus quitensis). Whereas the hair grass benefits from being wind pollinated, the Antarctic pearlwort has had to get creative with its reproductive needs. Instead of relying on pollinators, which simply aren’t present in any abundance on Antarctica, it appears that the pearlwort has shifted over to being entirely self-pollinated. This seems to work for it because if the mother plant is capable of living on Antarctica, so too will its clonal offspring.

By far the dominant plant life on the continent are the mosses. With 100 species known to live on Antarctica, it is hard to make generalizations about their habits other than to say they are pretty tough plants. Most live out their lives among the saturated rocks of the intertidal zones. What we can say about these mosses is that they support a bewildering array of microbial life, from fungi and lichens to protists and tardigrades. Even in this frozen corner of the world, plants form the foundation for all other forms of life.

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Antarctic pearlwort ( Colobanthus quitensis )

Antarctic pearlwort (Colobanthus quitensis)

The coastal plant communities of Antarctica represent hotbeds of biodiversity for this depauperate continent. They reach their highest densities on the Antarctic Peninsula as well as on coastal islands such as south Orkney Islands and the South Shetland Islands. Here, conditions are just mild enough among the various rocky crevices for germination and growth to occur. Still, life on Antarctica is no cake walk. A short growing season, punishing waves, blistering winds, and trampling by penguins and seals present quite a challenge to Antarctica’s botanical denizens. They are able to live here despite these challenges.

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Still, humans take their toll. The Antarctic Peninsula is experiencing some of the most rapid warming on the planet over the last century. As this region grows warmer and drier each year, plants are responding accordingly. Antarctic mosses along the peninsula are increasingly showing signs of stress. They are starting to prioritize the production of protective pigments in their tissues over growth and reproduction. Moreover, new species of moss are starting to take over. Rapid warming and drying of the Antarctic Peninsula appears to be favoring species that are more desiccation tolerant at the expense of the continents endemic moss species.

Changes in the structure and composition of Antarctica’s moss beds is far from being a scientific curiosity for only bryologists to ponder. It is a symptom of greater changes to come.

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

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

Hydrostachyaceae: Enigmatic Rheophytes

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Today I would like to introduce you to an enigmatic family of aquatic angiosperms called Hydrostachyaceae. Though they kind of look like strange aquatic ferns or perhaps even lycopods, they are actually strange flowering plants. To find them, you need to hang out around waterfalls and rapids in either Madagascar or southern Africa.

Hydrostachyaceae is made up of roughly 22 species. This is a poorly understood group of plants and there is always a chance that more species await discovery. The various members of Hydrostachyaceae all take on a similar appearance. For much of the year they exist as a set of feathery, fern-like leaves that grow surprisingly large and look quite delicate, especially considering the types of habitats in which they grow.

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Their delicate appearance is deceptive. In fact, the feathery structure of their leaves is an adaptation to the waters in which they grow. These are plants that require fast moving, clean, fresh water. If they were to produce flat, unbroken leaves, the fast currents would quickly rip them to shreds. By producing long, feathery leaves, water simply flows right over them with minimal disturbance. However, their preferred habitats also make them extremely difficult to study. Hence we know very little about their ecology.

What we do know about these plants is that they need clean rock surfaces and clear water for germination and subsequent growth. Dump too much sediment in the stream and you can kiss these plants goodbye. When they dry season approaches and water levels begin to drop, these oddball plants go into flowering mode. To the best of my knowledge, nearly all members of this family are dioecious, meaning individual plants are either male or female. When it comes time to flower, each plant produces modest sized spikes densely packed with flower.

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The spikes themselves sit up and above the water line, which is how this family and genus got its name. Hydrostachys is Greek and roughly translates to “water spike.” I have not been able to track down any solid information on what might be pollinating these blooms, however, given their small, dense nature, and the extreme places in which they live, my bet would be on wind.

The ecology of Hydrostachyaceae isn’t the only mystery about these plants. Their position on the tree of life has also been cause for confusion ever since they were discovered. Morphologically speaking, aquatic angiosperms can offer a lot of confusion to taxonomists. Like whales, the ancestors of aquatic angiosperms lived out their lives on land. Making the move back into water comes with a lot of extremely specialized adaptations that can cloud our morphological interpretations of things.

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Some authors have put forth the idea that these plants belong to another family of highly derived aquatic angiosperms - the Podostemaceae. However, genetic analyses paint a much different story. When the Angiosperm Phylogeny Group got a hold of specimens, their molecular work suggested the Hydrostachyaceae were nestled in Cornales, somewhere near the Hydrangea family (Hydrangeaceae). Exactly where Hydrostachyaceae fits into this new classification is still up for debate but it just goes to show you how messy things can get when plant lineages return to water.

Sadly, like so many other plants, the various members of Hydrostachyaceae are under a lot of pressure in the wild. Basically anything that threatens the quality of streams and rivers is a threat to the ongoing survival of these species. Runoff pouring into water ways from agriculture and mining cloud up the water and bury available germination sites under layers of sediment. Things only get worse when hydroelectric projects are installed. The fate of these plants is unequivocally tied to water quality.

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

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

A Relictual Palm in the American Southwest

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Scattered throughout hidden oases nestled in the southwest corner of North America grows a glorious species of palm known to science as Washingtonia filifera. This charismatic tree goes by a handful of common names such as the desert fan palm, petticoat palm, and California fan palm. No matter what you call it, there is no denying that this palm is both unique and important to this arid region.

Populations of the desert fan palm are few and far between, occurring in a few scattered locations throughout the Colorado and Mojave Deserts. This palm can’t grow just anywhere in these deserts either. Instead, its need for water restricts it to small oases where springs, streams, or a perched water table can keep them alive.

Fossil evidence from Wyoming suggests that the restricted distribution of this palm is a relatively recent occurrence. Though not without plenty of debate, our current understanding of the desert fan palm is that it could once be found growing throughout a significant portion of western North America but progressive drying has seen its numbers dwindle to the small pockets of trees we know today.

The good news is that, despite being on conservation lists for its rarity, the desert fan palm appears to be expanding its range ever so slightly. One major component of this range expansion has to do with human activity. The desert fan palm makes a gorgeous specimen plant for anyone looking to add a tropical feel to their landscape. As such, it has been used in plantings far outside of its current range. Some reports suggest that it is even becoming naturalized in places like Death Valley, Sonoran Mexico, and even as far away as Florida and Hawai’i.

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Other aspects contributing to its recent range expansion are also attributable to human activity, though indirectly. For one, with human settlement comes agriculture, and with agriculture comes wells and other forms of irrigation. It is likely that the seeds of the desert fan palm can now find suitably wet areas for germination where they simply couldn’t before. Also, humans have done a great job at providing habitat for potential seed dispersers, especially in the form of coyotes and fruit-eating birds.

It’s not just an increase in seed dispersers that may be helping the desert fan palm. Pollinators may be playing a role in its expansion as well, though in a way that may seem a bit counterintuitive. With humans comes a whole slew of new plants in the area. This greatly adds to the floral resources available for insect pollinators like bees.

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Historically it has been noted that bees, especially carpenter bees, tend to be rather aggressive with palm inflorescences as they gather pollen, which may actually reduce pollination success. It is possible that with so many new pollen sources on the landscape, carpenter bees are visiting palm flowers less often, which actually increases the amount of pollen available for fertilizing palm ovules. This means that the palms could be setting more seed than ever before. Far more work will be needed before this mechanism can be confirmed.

Aside from its unique distribution, the desert fan palm has an amazing ecology. Capable of reaching heights of 80 ft. (25 m) or more and decked out in a skirt of dead fronds, the desert fan palm is a colossus in the context of such arid landscapes. It goes without saying that such massive trees living in desert environments are going to attract their fair share of attention. The thick skirt of dead leaves that cloaks their trunks serve as vital refuges for everything from bats and birds, to reptiles and countless of insects. Fibers from its leaves are often used to build nests and line dens.

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And don’t forget the fruit! Desert fan palms can produce copious amount of hard fruits in good years. These fruits go on to feed many animals. Coupled with the fact that the desert fan palm always grows near a water source and you can begin to see why these palms are a cornerstone of desert oases. There has been some concern over the introduction of an invasive red palm weevil (Rhynchophorus ferrugineus), however, researchers were able to demonstrate that the desert fan palm has a trick up its sleeve (leaf skirt?) for dealing with these pests.

It turns out that desert fan palms are able to kill off any of these weevils as they try to burrow into its trunk. The desert fan palm secretes a gummy resin into damaged areas, which effectively dissuaded most adults and killed off developing beetle larvae. For now it seems that resistance is enough to protect this palm from this weevil scourge.

It is safe to say that regardless of its limited distribution, the desert fan palm is one tough plant. Its towering trunks and large, fan-like leaves stand as a testament to the wonderful ways in which natural selection shapes organisms. It is a survivor and one that has benefited a bit from our obsession with cultivating palms.

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

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


Are Packrats Fumigating Their Homes Using Plants?

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Any organism that lives in one place for a long enough time is going to have to deal with pests. For mammals, this often means fleas and ticks. Nests, dens, and other roosting spots tend to accumulate high numbers of these blood suckers the longer they are in use. As such, anything that can cut down on pest loads in and around the home has the potential to confer great advantages. Evidence from California suggests that wood rats may be using the leaves of a shrub to do just that.

Dusky-footed wood rats (A.K.A. packrats) build giant nests out of twigs and other plant debris. These nests serve to protect packrats from both the elements and hungry predators. Packrat nests can last for quite a long time and reach monumental proportions considering the size of the rat itself. Because they use these stick nests for long periods of time, it should come as no surprise that they can build up quite a pest load. Fleas are especially problematic for these rodents.

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A dusky-footed woodrat ( Neotoma fuscipes ) and its den.

A dusky-footed woodrat (Neotoma fuscipes) and its den.

When researchers took a closer look at what packrats were bringing into their nests, they realized that not all plant material was treated equally. Whereas packrats actively collect and feed on leaves from various oaks (Quercus spp.), conifers (Pinus spp., Juniperus spp., etc.), and toyon (Heteromeles arbutifolia), the packrats seemed to have a special affinity for the leaves of the California bay (Umbellularia californica). However, instead of taking huge bites out of bay leaves, the rats appear to nibble them along the margin and spread them throughout their nest. What’s more, fresh bay leaves are brought in every few days.

This led some researchers to suggest that, instead of packrats using bay leaves as food, they may be using them to fumigate their homes. Indeed, California bay is rather chemically active. It is an aromatic shrub noted for its resistance to insect infestation. Of special interest to the research team were a group of chemical compounds called monoterpenoids. They noted that bay leaves were especially high in two types of of these compounds - 1,8-cineole (which gives the shrub its characteristic odor), and umbellulone (which has shown to be quite toxic to rodents). Why else would packrats bring something potentially deadly into their home other than to drive off pests?

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Closer observation revealed that the packrats were in fact treating bay leaves differently than other leaves. For starters, bay leaves were disproportionately used to line the sleeping chambers within the stick nests. What’s more, the bay leaves were cycled out every 2 to 3 days. Even the nibbling patterns were significantly different. As mentioned above, bay leaves were merely nibbled along the leaf margins, which is an ideal place to nibble if releasing volatile compounds is the desired effect.

When researchers tested the effectiveness of a variety of leaves in the lab, their results added further evidence to the fumigation hypothesis. More than any other leaf found in packrat nests, bay leaves had clear negative effects on flea numbers. Flea survival in the lab was reduced by upwards of 75% when California bay leaves were present whereas flea survival was only reduced by less than 10% with all other leaves. It goes without saying that, whether they are conscious decisions or not, packrats definitely stand to benefit by decorating their homes with California bay leaves.

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

Further Reading: [1]

Arctic Vegetation is Growing Taller & Why That Matters

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The Arctic ecosystem is changing and it is doing so at an alarming rate. Indeed, the Arctic Circle is warming faster than most other ecosystems on this planet. All of this change has implications for the plant communities that call this region home. In a landmark study that incorporated thousands of data points from places like Alaska, Canada, Iceland, Scandinavia, and Russia, researchers have demonstrated that Arctic vegetation is, on average, getting taller.

Imagine what it is like to be a plant growing in the Arctic. Extreme winds, low temperatures, a short growing season, and plenty of snow are just some of the hardships that characterize life on the tundra. Such harsh conditions have shaped the plants of this region into what we know and love today. Arctic plants tend to hug the ground, hunkering down behind whatever nook or cranny offers the most respite from their surroundings. As such, plants of Arctic-type habitats tend to be pretty small in stature. As you can probably imagine, if these limits to plant growth become less severe, plants will respond accordingly.

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That is part of what makes this new paper so alarming. The vegetation that comprise these Arctic communities is nearly twice as tall today as it was 30 years ago. However, the increase in height is not because the plants that currently grow there are getting taller but rather because new plants are moving northwards into these Arctic regions. New players in the system are usually cause for concern. Other studies have shown that it isn’t warming necessarily that hurts Arctic and alpine plants but rather competition. They simply cannot compete as well with more aggressive plant species from lower latitudes.

Taller plants moving into the Arctic may have even larger consequences than just changes in species interactions. It can also change ecosystem processes, however, this is much harder to predict. One possible consequence of taller plants invading the Arctic involves carbon storage. It is possible that as conditions continue to favor taller and more woody vegetation, there could actually be more carbon storage in this system. Woody tissues tend to sequester more carbon and shading from taller vegetation may slow decomposition rates of debris in and around the soil.

Alopecurus alpinus  is one of the new tall plant species moving into the Arctic

Alopecurus alpinus is one of the new tall plant species moving into the Arctic

It is also possible that taller vegetation will alter snowpack, which is vital to the health and function of life in the Arctic. Taller plants with more leaf area could result in a reduced albedo in the surrounding area. Lowering the albedo means increased soil temperatures and reduced snowpack as a result. Alternatively, taller plants could also increase the amount of snowpack thanks to snow piling up among branches and leaves. This could very well lead (counterintuitively) to warmer soils and higher decomposition rates as snowpack acts like an insulating blanket, keeping the soil slightly above freezing throughout most of the winter.

It is difficult to make predictions on how a system is going to respond to massive changes in the average conditions. However, studies looking at how vegetation communities are responding to changes in their environment offer us one of the best windows we have into how ecosystems might change moving into the uncertain future we are creating for ourselves.

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

Further Reading: [1]

The Only True Cedars

Cedrus deodara

Cedrus deodara

The only true cedars on this planet can be found growing throughout mountainous regions of the western Himalayas and Mediterranean. All others are cedars by name only. The so-called “cedars” we encounter here in North America are not even in the same family as the true cedars. Instead, they belong to the Cypress family (Cupressaceae). The true cedars all belong to the genus Cedrus and are members of the family Pinaceae. They are remarkable trees with tons of ecological and cultural value.

J. White,1803-1824.

J. White,1803-1824.

The true cedars are stunning trees to say the least. They regularly reach heights of 100 ft. (30 m.) or more and can live for thousands of years. Cedars exhibit a dimorphic branching structure, with long shoots forming branches and smaller shoots carrying most of the needle load. The needles themselves are borne in dense, spiral clusters, giving the branches a rather aesthetic appearance. Each needle produces layers of wax, which vary in thickness depending on how exposed the tree is growing. This waxy layer helps protect the tree from sunburn and desiccation.

Cedrus libani

Cedrus libani

Cedrus libani

Cedrus libani

One of the easiest ways to identify a cedar is by checking out its cones. All members of the genus Cedrus produce upright, barrel-shaped cones. Male cones are smaller and don’t stay on the tree for very long. Female cones, on the other hand, are quite large and stay on the tree until the seeds are ripe. Upon ripening, the entire female cone disintegrates, releasing the seeds held within. Each seed comes complete with blisters full of distasteful resin, which is thought to deter seed predators.

Male cones of  Cedrus atlantica

Male cones of Cedrus atlantica

Female  Cedrus  cones.

Female Cedrus cones.

In total, there are only four recognized species of cedar - the Atlas cedar (Cedrus atlantica), the Cyprus cedar (C. brevifolia), the deodar cedar (C. deodara), and the Lebanon cedar (C. libani). I have heard arguments that C. brevifolia is no more than a variant of C. libani but I have yet to come across any source that can say this for certain. Much more work is needed to assess the genetic structure of these species. Even their place within Pinaceae is up for debate. Historically it seems that Cedrus has been allied with the firs (genus Abies), however, work done in the early 2000’s suggests that Cedrus may actually be sister to all other Pinaceae. We need more data before anything can be said with certainty.

Cedrus atlantica

Cedrus atlantica

Regardless, two of these cedars - C. atlantica & C. libani - are threatened with extinction. Centuries of over-harvesting, over-grazing, and unsustainable fire regimes have taken their toll on wild populations. Much of what remains is not considered old growth. Gone is the heyday of giant cedar forests. Luckily, many populations are now located in protected areas and reforestation efforts are being put into place throughout their range. Still, the ever present threat of climate change is causing massive pest outbreaks in these forests. The future for these trees hangs in the balance.

Photo Credit: Wikimedia Commons

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