Recently, a new species of Hydrostachys plants was identified by the Sino-Africa Joint Research Center. Based on detailed morphological and phylogenetic studies, the research results were published in the international journal of plant taxonomy: PhytoKeys, entitled "Hydrostachys Flabellifera (Hydrostachyaceae), a New Species from Madagascar". 

Madagascar is the fourth largest island in the world, and is famous for its exceptional biodiversity. This island has been recognized for many years as a unique centre of diversity and endemism. There are 243 families, 1730 genera and 11220 species of vascular plants distributed in Madagascar, among which, 10319 are indigenous angiosperms. Eighty-four percent of the indigenous angiosperms are endemic to Madagascar, and the rest are mostly confined to Africa as well. 

Hydrostachys is the sole genus in the family Hydrostachyaceae with about 22 known species, more than half of the species are endemic to Madagascar and the remaining species are native to Africa. Hydrostachys plants are often used in traditional medicine by local people and some researches have shown that it may have a therapeutic effect on cancer.  

The plants of Hydrostachys, which live in fast moving streams or rivers, are well adapted to turbulent aquatic environments with their roots and discoidal rhizome adhering to the rocks. Their leaves are simple or pinnate, emerging from the rhizome. Their petiole, rachis and subdivisions are often covered with diverse forms of emergences, including verrucae, scales and lobules. Spikes with only a few unisexual flowers are usually emerging from the rhizome as well, and the flowers are highly degraded without sepals and petals; the fruit is a capsule and a large number of tiny seeds grow in it. 

During a field investigation in Central Madagascar in 2017, a Hydrostachys population was found, which appeared similar to H. verruculosa and H. laciniata but can be clearly distinguished, and its unique individual morphological characteristics has caught the investigators’ attention.  

After careful specimen comparison and extensive literature review, it is found that its leaf structure is different from that of all known species in this genus, and it can also be easily distinguished from similar species by its short leaves (only 3-12 cm long) and rachis with spirally-arranged, flabelliform subdivisions.  

To determine its systematic position in the genus Hydrostachys, the authors sequenced internal transcribed spacer (ITS) gene from nine Hydrostachys species and selected three taxa from Nyssa and one from Triphyophyllum as outgroups to construct phylogenetic trees.  

The results of molecular systematics also support it as a new species of the genus. Therefore, this new species is named Hydrostachys flabellifera according to its obvious flabelliform subdivisions. 

Hydrostachys flabellifera G.W. Hu, Zhun Xu & Q.F. Wang A habit B emergences on rachis, cross-section C, D emergences E dorsal view of male bract F ventral view of male bract G top view of stamen (Image by Sino-Africa Joint Research Center )