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]

Palo Verde

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One of the first plants I noticed upon arriving in the Sonoran Desert were these small spiny trees without any leaves. The reason they caught my eye was that every inch of them was bright green. It was impossible to miss against the rusty brown tones of the surrounding landscape. It didn’t take long to track down the identity of this tree. What I was looking at was none other than the palo verde (Parkinsonia florida).

Palo verde belong to a small genus of leguminous trees. Parkinsonia consists of roughly 12 species scattered about arid regions of Africa and the Americas. The common name of “palo verde” is Spanish for “green stick.” And green they are! Like I said, every inch of this tree gives off a pleasing green hue. Of course, this is a survival strategy to make the most of life in arid climates.

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Despite typically being found growing along creek beds, infrequent rainfall limits their access to regular water supplies. As such, these trees have adapted to preserve as much water as possible. One way they do this is via their deciduous habit. Unlike temperate deciduous trees which drop their leaves in response to the changing of the seasons, palo verde drop their leaves in response to drought. And, as one can expect from a denizen of the desert, drought is the norm. Leaves are also a conduit for moisture to move through the body of a plant. Tiny pours on the surface of the leaf called stomata allow water to evaporate out into the environment, which can be quite costly when water is in short supply.

The tiny pinnate leaves and pointy stems of the palo verde. 

The tiny pinnate leaves and pointy stems of the palo verde. 

Not having leaves for most of the year would be quite a detriment for most plant species. Leaves, after all, are where most of the photosynthesis takes place. That is, unless, you are talking about a palo verde tree. All of that green coloration in the trunk, stems, and branches is due to chlorophyll. In essence, the entire body of a palo verde is capable of performing photosynthesis. In fact, estimates show that even when the tiny pinnate leaves are produced, a majority of the photosynthetic needs of the tree are met by the green woody tissues.

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Flowering occurs whenever there is enough water to support their development, which usually means spring. They are small and bright yellow and a tree can quickly be converted into a lovely yellow puff ball seemingly overnight. Bees relish the flowers and the eventual seeds they produce are a boon for wildlife in need of an energy-rich meal.

However, it isn’t just wildlife that benefits from the presence of these trees. Other plants benefit from their presence as well. As you can probably imagine, germination and seedling survival can be a real challenge in any desert. Heat, sun, and drought exact a punishing toll. As such, any advantage, however slight, can be a boon for recruitment. Research has found that palo verde trees act as important nurse trees for plants like the saguaro cactus (Carnegiea gigantea). Seeds that germinate under the canopy of a palo verde receive just enough shade and moisture from the overstory to get them through their first few years of growth.

In total, palo verde are ecologically important trees wherever they are native. What’s more, their ability to tolerate drought coupled with their wonderful green coloration has made them into a popular tree for native landscaping. It is certainly a tree I won’t forget any time soon.

Further Reading: [1] [2]

Screw Pines, Volcanism, and Diamonds

The association between geology and botany has always fascinated me. The closer you look, the more you can't separate the two. Rocks and minerals influence soil characteristics, which in turn influences which plant species will grow and where, which in turn influences soil properties. Take for instance the case of kimberlite.

Kimberlite is a volcanic rock whose origin is quite intense. Kimberlite is found in the form of large vertical columns, often referred to as pipes. They are the result of some seriously explosive volcanism. Intense heat and pressure builds deep within the mantle until it explodes upward, forming a column of this igneous rock. 

Over long spans of time, these pipes begin to weather and erode. This results in soil that is rich in minerals like magnesium, potassium, and phosphorous. As anyone who gardens can tell you, these are the ingredients of many fertilizers. In Africa where these sorts of pipes are well known, there is a species of plant that seems to take advantage of these conditions. 

It has been coined Pandanus candelabrum and it belongs to a group of plants called the screw pines. They aren't true pines but are instead a type of angiosperm. Now, the taxonomy of the genus Pandanus is a bit shaky. Systematics within the family as a whole has largely been based on fragmentary materials such as fruits and flowers. What's more, for much of its taxonomic history, each new collection was largely regarded as a new species. You might be asking why this is important. The answer has something to do with the kimberlite P. candelabrum grows upon. 

There is something other than explosive volcanic activity that makes kimberlite famous. It is mostly known for containing diamonds. In a 2015 paper, geologist Stephen E. Haggerty made this connection between P. candelabrum and kimberlite. As far as anyone can tell, the plant is a specialist on this soil type. As such, prospectors are now using the presence of this plant as a sort of litmus test for finding diamond deposits. This is why I think taxonomy becomes important. 

If P. candelabrum turns out not to be a unique species but rather a variation then perhaps this discovery doesn't mean much for the genus as a whole. However, if it turns out that P. candelabrum is a truly unique species then this new-found association with diamond-rich rocks may spell disaster. Mining for diamonds is a destructive process and if every population of P. candelabrum signals the potential for diamonds, then the future of this species lies in the balance of how much our species loves clear, shiny chunks of carbon. A bit unsettling if you ask me. 

Photo Credit: to.pbs.org/1NQUXqU

Further Reading:
http://econgeol.geoscienceworld.org/content/110/4/851.full

The Smallest and Rarest Water Lily

Nymphaea thermarum is both the smallest and the rarest water lily in the world. It is so rare that it no longer exists in the wild. Back in 1987 it was discovered growing in the mud of a hot spring located in Rwanda, Africa. The botanist who discovered it, Eberhard Fischer, realized that it was quite rare and collected a few specimens to bring back to Germany. Indeed it has never been found growing anywhere else. This was a wise decision on his part because after decades of habitat degradation, the hot spring was destroyed by locals in order to divert water for laundry. 

For years, the original specimens were not doing so hot in captivity. It was looking like this species was going to be lost forever. That was until a handful of seedlings ended up in the hands of plant germination specialist Carlos Magdalena of the Royal Botanical Gardens at Kew. Carlos saw a challenge in this species and realized that his efforts could possibly be the last chance this species had at survival. 

Carlos tried many avenues of approach to growing this species and none seemed to be working. He messed with water chemistry, nutrients, and water depth, all the while the plants seemed to languish, never reaching maturity. In a final attempt to make things work, Carlos returned to the original literature. Here he found something interesting. Apparently, N. thermarum was not growing in water at all. Instead, it seemed to only grow in the wet mud surrounding the hot spring. 

This was the key that unlocked the door to propagating this species. Instead of growing this water lily submerged like every other water lily species, Carlos decided to grow the plants as they once grew in the wild, in mud. This was it! Carlos successfully grew 8 new plants to maturity. This may seem like a small amount but for the last remaining members of a species, every little bit counts. Recently in 2009, the first of Carlos's plants flowered. This marked a milestone for this species. While it has been wiped out in the wild, this species can still persist in cultivation until experts can decide on what the best course of action is for its future. 

Further Reading:
http://www.kew.org/science-conservation/plants-fungi/nymphaea-thermarum

Feed Me, Seymour!

In the spirit of spooky-ness, today I would like to introduce you to one of the creepiest plants that I know of. I spent a lot of time debating on which species could be considered the "creepiest" but after much deliberation I decided it was Hydnora africana.

This plant has no common name but regardless, the ecology of this species is quite fascinating. Hydnora africana is native to southern Africa and as you can probably tell from the picture, it produces no leaves and no chlorophyll. Instead of wasting energy on producing its own food, H. africana has resorted to parasitism. It is a root parasite on members of the family Euphorbiaceae. It taps into the roots of a host plant using specialized structures called "haustoria." In this way they are able to gather all their nutritional needs from their host. Once H. africana has obtained enough energy it will produce a flower.

The flower is all you will ever see of this plant. The strange, scaly structure emerges from the ground underneath its host. Three slits begin to form, each lined with white, hair-like structures. At first these structures remain intact. The spaces between are just big enough to allow entry of pollinators, which in this case are dung beetles. Once the flower opens these slits it begins to produce some heat, not unlike what we see in many aroids. The heat helps to spread the scent and the smell is what you would expect from a plant trying to attract dung beetles - it smells like feces.

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When a beetle arrives looking for some fresh poop, it enters the flower through those slits and falls down into the trap. The rest of the flower consists of a tube-like structure underground. To keep the beetles from escaping H. africana employs a trick used by many carnivorous pitcher plants. Lining the walls are downward pointing hairs that prevent the beetles from crawling out before their job is complete. Once inside, the beetles are drawn to the center where the smell is emitted. Here they are generously dusted with pollen. If the beetles have arrived after a previous H. africana visit then they will also deposit pollen and thus pollination is achieved. Once the plant releases pollen onto the beetles, the hairs lining the wall relax and the slits open completely, allowing the beetles to escape.

I hope some day to see this plant in person. To the best of my knowledge it has only been grown in captivity once. Seeds were sown in a pot containing a known host species of Euphorbia. It took a very long time for germination and even longer to mature and produce a flower. Either way this creepy species is actually quite fascinating.

Photo Credit: [1] [2]

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

A Strange Gymnosperm From Africa

What you are looking at here is not just a pile of discarded leaves. It is indeed a living plant. Would you believe me if I told you that it is a distant relative of pines, spruces, larches and firs? It's true! This right here is Welwitschia mirabilis, a representative of an ancient lineage of gymnosperm!

Welwitschia is endemic to the Namib Desert of Africa. It is hard to picture any plant living in such a dry area. In some years it never even rains. Welwitschia persists despite this fact. It tends to grow in watercourses and outcrops, thus enabling it to gather what precious little rain does fall. It has a deep taproot suggesting that it relies heavily on ground water. The leaves of Welwitschia also have high amounts of stomata on both surfaces enabling it to absorb water directly from the fog that regularly blows through when colder air currents mix with hot air from the desert.

For a long time it was believed that Welwitschia represented true neoteny, which is the retention of juvenile characteristics into adulthood. It was thought that Welwitschia was nothing more than a sexually mature seedling with exaggerated cotyledons. This idea was later abandoned when Martens showed that Welwitschia do develop further than the seedling stage. What really happens is the apical bud, which is responsible for vertical growth in plants, dies quite early on in development. In essence, Welwitschia has lost its "head."

I was not kidding when I said that Welwitschia is a gymnosperm. Once sexual maturity is reached, cones are produced. Individual plants are either male or female and unlike many of its relatives, Welwitschia is not wind pollenated. Instead it relies on insects to transfer pollen from male cones to female cones.

Probably the most remarkable aspect of Welwitschia ecology is its longevity. Individual plants can live well over 1000 years. Some individuals are estimated at around 2000 years old! In such a harsh desert environment, persistence is the key to survival for Welwitschia.

Photo Credit: Petr Kosina

Further Reading:
http://www.jstor.org/discover/10.2307/2442386…

http://www.plantzafrica.com/plantwxyz/welwitschia.htm