Checklist to the Elatostema (Urticaceae) of Vietnam including 19 new records, ten new combinations, two new names and four new synonyms

Abstract

Elatostema (Urticaceae) comprises several hundred herbaceous species 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 Taxonomic revisions of Elatostema are largely out of date and contradict each other with respect to the delimitation of Elatostema and Pellionia.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. As part of a broader revision of Elatostema in SE Asia, we present an updated checklist for Vietnam based on field visits, 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; this level of endemism is comparable to levels observed in Orchidaceae. 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. The relationship among floristic regions is also investigated. We could find no records of Elatostema for 33 out of 63 provincial units of Vietnam, including all the southernmost provinces. We propose that further studies on the diversity of Elatostema in central and southern Vietnam are severely needed.

Keywords: Begonia; Elatostemateae; Flora of Vietnam; Indochina; Karst; Lectotypification; Limestone; Orchidaceae; Pellionia; Taxonomy.

Figure 1. Climate map of Vietnam.

The data based on Nguyen et al. (2000) showing seven types of climate in Vietnam.

Figure 2. Map of floristic regions in Vietnam.

The data modified from Averyanov et al. (2003c) showing six floristic regions in Vietnam.

Figure 3. Plate I of representative Elatostema species in Vietnam: (A) E. crassiusculum; (B) E. glochidioides; (C) E. hookerianum; (D) E. prunifolium; (E), E. arcuatobracteatum; (F), E. retrohirtum; (G), E. obtusum; (H) E. ramosum; (I) E. integrifolium; (J) E. fengshanense; (K) E. austrosinense; (L) E. malacotrichum.

Figure 4. Plate II of representative Elatostema species in Vietnam: (A) E. heterolobum; (B), E. atroviride; (C) E. tenuicaudatum; (D) E. nasutum; (E) E. cyrtandrifolium; (F) E. backeri; (G), E. veronicoides; (H) E. dissectum; (I) E. atropurpureum; (J) E. paucidentatum; (K) E. lineolatum; (L) E. xanthophyllum.

Figure 5. Plate III of representative Elatostema species in 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.

Figure 6. Variation in Elatostema species richness and endemism across provinces of Vietnam.

The tones of green indicate number of species per province. The red figures in brackets indicate number of national endemic species recorded for a province where it is non-zero.

Figure 7. Proportion of diversity and endemism and the relationship of the floristic regions.

Large circles designate floristic regions. Percentage numbers above the line in the large circles indicate the relative proportion of diversity occurring in a certain region (within Vietnam); percentage numbers below the line indicate the relative proportion of national endemics occurring in a certain region; percentage numbers in the small circles indicate the relative proportion of co-exsisted species occurring in the pairs of region connected by the line and show their relative floristic relationships.