A New Species of Waterfall Specialist Has Been Discovered In Africa

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At first glance, this odd plant doesn’t look very special. However, it is the first new member of the family Podostemaceae to be found in Africa in over 30 years. It has been given the name Lebbiea grandiflora and it was discovered during a survey to assess the impacts of a proposed hydroelectric dam. By examining the specimen, Kew botanists quickly realized this plant was unique. Sadly, if all goes according to plan, this species may not be long for this world unless something is done to preserve it.

Members of the family Podostemaceae are strange plants. Despite how delicate they look, these plants specialize in growing submersed on rocks in waterfalls, rapids, and other fast flowing bodies of water. They are generally small plants, though some species can grow to lengths of 3 ft. (1 m) or more. The best generalization one can make about this group is that they like clean, fast-flowing water with plenty of available rock surfaces to grow on.

Lebbiea grandiflora certainly fits this description. It is native to a small portion of Sierra Leone and Guinea where it grows on slick rock surfaces only during the wet season. As the dry season approaches and the rivers shrink in size, L. grandiflora quickly sets seed and dies.

As mentioned, the area in which this plant was discovered is slated for the construction of a large hydroelectric dam. The building of this dam will most certainly destroy the entire population of this plant. As soon as water slows, becomes more turbid, and sediments build up, most Podostemaceae simply disappear. Unfortunately, I appears this plant was in trouble even before the dam came into the picture.

A. habit, whole plant, in fruit, showing the flat root, a pillar-like ‘haptera’, and a shoot with three inflorescences, B. detail of shoot with three branches, C. view of upper surface of a flattened root, with six short, erect shoots, each with 1–2 1-flowered inflorescences emerging from spathellum remains, D. side view of plant showing, on the lower surface of the flattened root, the pillar-like haptera, branched at base; upper surface of root with spathellum-sheathed inflorescence base, E. plant attached to rock by weft of thread-like root hairs (indicated with arrow) from base of pillar-like haptera; upper surface of flattened root with two shoots, F. side view of flower showing one of two tepals in full frontal view, G. as F. with tepal removed, exposing the gynoecium with, to left, the arched-over androecium, H. side view of flower with androecium in centre, two tepals flanking the gynoecium, I. androecium (leftmost of three anthers missing), J. transverse section of andropodium, K. view of gynoecium from above showing funneliform style-stigma base, L. fruit, dehisced, M. transverse section of bilocular fruit, showing septum and placentae, N. placentae with seeds, divided by septum, O. seeds, P. seed with mucilage outer layer. Drawn by Andrew Brown from  Lebbie  A2721  [SOURCE]

A. habit, whole plant, in fruit, showing the flat root, a pillar-like ‘haptera’, and a shoot with three inflorescences, B. detail of shoot with three branches, C. view of upper surface of a flattened root, with six short, erect shoots, each with 1–2 1-flowered inflorescences emerging from spathellum remains, D. side view of plant showing, on the lower surface of the flattened root, the pillar-like haptera, branched at base; upper surface of root with spathellum-sheathed inflorescence base, E. plant attached to rock by weft of thread-like root hairs (indicated with arrow) from base of pillar-like haptera; upper surface of flattened root with two shoots, F. side view of flower showing one of two tepals in full frontal view, G. as F. with tepal removed, exposing the gynoecium with, to left, the arched-over androecium, H. side view of flower with androecium in centre, two tepals flanking the gynoecium, I. androecium (leftmost of three anthers missing), J. transverse section of andropodium, K. view of gynoecium from above showing funneliform style-stigma base, L. fruit, dehisced, M. transverse section of bilocular fruit, showing septum and placentae, N. placentae with seeds, divided by septum, O. seeds, P. seed with mucilage outer layer. Drawn by Andrew Brown from Lebbie A2721 [SOURCE]

As mentioned, Podostemaceae need clean rock surfaces on which to germinate and grow. Without them, the seedlings simply can’t get established. Mining operations further upstream of the Sewa Rapids have been dumping mass quantities of sediment into the river for years. All of this sediment eventually makes it down into L. grandiflora territory and chokes out available germination sites.

Alarmed at the likely extinction of this new species, the Kew team wanted to try and find other populations of L. grandiflora. Amazingly, one other population was found growing in a river near Koukoutamba, Guinea. Sadly, the discovery of this additional population is bitter sweet as the World Bank is apparently backing another hydro-electric dam project on that river as well.

The only hope for the continuation of this species currently will be to (hopefully) find more populations and collect seed to establish ex situ populations both in other rivers as well as in captivity if possible. To date, no successful purposeful seeding of any Podostemaceae has been reported (if you know of any, please speak up!). Currently L. grandiflora has been given “Critically Endangered” status by the IUCN and the botanists responsible for its discovery hope that, coupled with the publication of this new species description, more can be done to protect this small rheophytic herb.

Photo Credit: [1] [2]

Further Reading: [1]

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]