Elatostema (Urticaceae) comprises several hundred species of succulent herbs and subshrubs that grow in shade in forests, gorges, stream sides and caves. There are currently ca. 600 accepted names within the genus Elatostema (Urticaceae). The genus is mainly distributed in tropical and subtropical Africa, Asia, Australia and Oceania. The greatest species richness occurs on limestone karst in Southeast Asia. Taxonomic revisions of Elatostema are largely out of date and contradict each other with respect to the delimitation of Elatostema and Pellionia. Most herbaria in SE Asia and worldwide contain significant amounts of unidentified material.
The delimitation of Elatostema has been controversial with respect to Elatostematoides, Pellionia and Procris. Using reconstruction of molecular phylogeny and re-evaluation of morphological characters of leaves, inflorescences and flowers, the latest study (Tseng et al., 2019) demonstrates that Elatostema is a monophyletic group which includes Pellionia but excludes Procris, Elatostematoides and Pellionia repens.
The first checklist of Elatostema in Vietnam (Gagnepain, 1930) documented 34 species
(together with Pellionia). This was followed by two studies (Ho, 2003; Hiep, 2005) which
documented 35 species and 32 species (together with Pellionia) respectively. Since that time
further 27 species have been recorded from Vietnam in regional floras and checklists and
other works The generic placement of some species was also reevaluated.
As part of a broader revision of Elatostema in SE Asia, botanists from Vietnam National Museum of Nature, Vietnam Academy of Science and Technology, and Guangxi Institute of Botany, China presented an updated checklist for Vietnam based on numerous field work through Vietnam (from 2009-2018), a review of specimens in herbaria worldwide, a review of type material and nomenclature. We recognize 77 taxa (75 species and two infraspecific taxa) of Elatostema in Vietnam, 23 of which were previously ascribed to Pellionia. Nineteen of these are new records for the country, i.e., E. attenuatoides, E. austrosinense, E. backeri, E. brunneinerve,
E. crassiusculum, E. crenatum, E. fengshanense, E. glochidioides, E. malacotrichum, E.
nanchuanense, E. oblongifolium, E. obtusum, E. oppositum, E. pergameneum, E. prunifolium, E. pseudolongipes, E. pycnodontum, E. salvinioides and E. xichouense. We place E. baviensis in synonymy of E. platyphyllum, E. colaniae in synonymy of E. myrtillus, P. macroceras in synonymy of E. hookerianum, and P. tetramera in synonymy of E. dissectum for the first time. Fourteen taxa (18% of all the recognized taxa) are endemic to Vietnam, which makes Elatostema one of the richest genera for endemic species in this country. Our checklist suggests that the highest diversity and endemism of Elatostema occurs in northern Vietnam, and that there is the greatest floristic similarity of northern Vietnam to SW China. We could find no records of Elatostema for 33 out of 63 provincial units of Vietnam, majority are the southernmost provinces. We propose that further studies on the diversity of Elatostema in central and southern Vietnam are severely needed.
These results have just published on the journal PeerJ. For further information, please visit the link:https://peerj.com/articles/6188/?utm_source=TrendMD&utm_campaign=PeerJ_TrendMD_0&utm_medium=TrendMD
Do Van Truong, PhD
Vietnam National Museum of Nature, Vietnam Academy of Science and Technology
Figure: Some new records of Elatostema for Vietnam. (A), E. caulialatum; (B), E. radicans; (C), E. tsoongii; (D), E. sinense; (E), E. brevifolium; (F), E. macintyrei; (G), E. balansae; (H), E. myrtillus; (I) E. platyphyllum; (J) E. petelotii; (K) E. longistipulum; (L) E. pseudolongipes
(Fu et al. 2019)