Rare Species of ‘Falls Orchid’ Declared Extinct in the Wild

Saxicolella deniseae was discovered in 2018 by botanist Denise Molmou, endemic to a waterfall on the Konkouré River in the Republic of Guinea, West Africa. The only known location of the plant has since been flooded by water from a dam built about 30 to 40 km downstream. Credit: Denise Molmou

A team of botanists from Guinea and the Royal Botanic Gardens, Kew in the UK have sounded the death knell for a plant of the genus Saxicolella endemic to a single location in Guinea. The sad discovery was made by Kew botanist Dr Martin Cheek, who investigated the last known coordinates of the plant using Google Earth satellite scans, following a taxonomic review of the genus Saxicolella published this week in the scientific journal. Kew Bulletin.

The article presents several species new to science, one of which is Saxicolella deniseae, or ‘Denise’s Saxicolella’. Unfortunately, the most recent satellite images dated November 2021 reveal that the plant was submerged by reservoir waters from a hydroelectric dam just 30-40 km downstream. According to Dr. Cheek, this development effectively led to the extinction of the plant.

The eight-species genus Saxicolella belongs to the “falls orchid” family which has about 300 species mostly in the tropics. Although not orchids, they are all restricted to falls and rapids. Officially known as the Podostemaceae, they are a family of waterfall plants restricted to life in fast, aerated waters, many of which are only now being described to science. The plants featured prominently in an episode of BBC’s The Green Planet documentary series earlier this year when naturalist David Attenborough called the family ‘orchids of the falls’.

Saxicolella deniseae was thought to be endemic to a single location along the Konkouré River in the Republic of Guinea, West Africa, which is now home to several newly constructed hydroelectric dams providing power to the region. The only known specimen was collected by (and named after) botanist Denise Molmou in 2018 – the first and likely last scientist to see the species in the wild – as part of the Guinea Tropical Important Areas program (TIPAs) – an international effort to conserve tropical plant biodiversity in the wild.

Dr Martin Cheek, Senior Research Manager in RBG Kew’s Africa team, says, “We know that many plant species have become extinct recently, but this case shows how sudden and unexpected extinction can be. In Africa, the species of ‘waterfall orchids’ are often confined to a single waterfall, sometimes two, three or four on the same river. In this case, because of the dam, several waterfalls along the Konkouré where the species might also have been found are now under hydroelectric reservoirs, so it seems fairly certain that this species is extinct. This probably happened last year, unbeknownst to us until now, when we checked how far the tank had advanced to the site.

Using satellite images and the Google Earth platform, Kew scientists found the coordinates of the plant’s discovery and compared images over the years since its discovery in 2018. Images from November 2021 indicates the area was flooded. Credit: Google Earth

Unfortunately, botanists have been unable to collect and store viable seeds that could preserve the genetic material of S. deniseae. Experts faced travel restrictions between 2020 and 2021 due to the COVID pandemic and Kew’s partners at the National Herbarium of Guinea were hampered by internal unrest from a military coup in September 2021. According to Dr Cheek, attempts by local botanists to reach the plant would have been further hampered by the exceptionally poor condition of the surrounding roads.

Denise Molmou, botanist at the UGAN-Herbier national de Guinée, says that “although it is a great honor to have a species that I discovered in the wild bearing my name, it is really sad that is almost certainly extinct. I will see if he can be found in other waterfalls, although the chances of finding him alive are not very high.

The falls on a tributary of the Konkouré River where S. deniseae was found were targeted because there were no known collections of this plant on most of the river, despite the existence of multiple falls visible on Google Earth. This indicated that no one had studied the biodiversity of plant life on the falls of this river.

To avoid the extinction of biodiversity in the wild, it is essential that botanists carry out comprehensive studies of waterfall plants in tropical areas, especially before the establishment of hydroelectric projects. Kew botanists believe it only takes one or two hours to survey a waterfall for ‘falls orchid’ species, followed by additional time to determine if they are threatened with extinction , news for science or not. Unfortunately, formal studies are rarely conducted before such projects come to fruition.

Dr Cheek says that “there is still a very small chance that this species will survive somewhere, somehow. But since this hydroelectric project, and another upstream, flooded about 150 km in length of the Konkouré River, as well as the 30 km of the tributary on which this species was present, it seems extremely likely that this species will be lost to never. We will continue to search.

Newly described species have a higher risk of extinction

More information:

Cheek, M., Molmou, D., Magassouba, S. et al. Taxonomic revision of Saxicolella (Podostemaceae), African plants of waterfalls strongly threatened by hydroelectric projects. Kew Bulletin (2022). doi.org/10.1007/s12225-022-10019-2

Provided by
Royal Botanic Gardens, Kew

Rare Species of ‘Falls Orchid’ Declared Extinct in the Wild (June 1, 2022)
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