Two new species of Elatostema (Urticaceae) from southeast Yunnan, China

Abstract Elatostema pleiophlebium and Elatostema malipoense, two endemic species from southeast Yunnan of China, are described and illustrated. Their diagnostic characters, description and relationship with morphologically similar species are also given. Elatostema pleiophlebium is easily recognised by its glabrous stem and leaf blade, and its longitudinally 1-ribbed outer staminate bracts. Elatostema malipoense is morphologically distinct for its tuberculate achene and pistillate receptacle which is puberulous. Both new species are known only from their type localities, and they are proposed to be classified as critically endangered.


Introduction
The genus Elatostema J. R. Forst. & G. Forst. is one of the largest genera of the family Urticaceae. This genus is characterized by the perianth lobes of female flowers being much shorter than the ovary or strongly reduced, and not corniculate at apex (Chen et al. 2003;Wang 1995). The staminate inflorescences play an important role in the delimitation of sections, but for delimiting series leaf venation, peduncle length, achene morphology and leaf reduction of staminate stem are used as main distinguishing characters (Wang 2011a).
Distribution and conservation status. Elatostema pleiophlebium is known only from the type locality near the Sanchahe river, Nanxi village, Hekou county, Yunnan. Consequently, it is probably an endemic species. A single population of a few hundred individuals was observed in an area of 1 km 2 . We believe therefore, that this new species is on the verge of extinction but we do not know if population size is stable or declining. Following the IUCN red list criteria (IUCN 2011), we propose to classify this species as critically endangered (CR B2ab (iii); C2b). Similar species. Elatostema pleiophlebium is a member of series Nanchuanensia W.T.Wang in sect. Elatostema (Wang 2011a). Elatostema pleiophlebium is similar to E. quinquecostatum W.T.Wang in having numerous lateral leaf nerves and a staminate capitulum involucre formed of six glabrous bracts. Elatostema quinquecostatum differs from E. pleiophlebium in having stems with strigose hairs, cuspidate leaf apices, hirsute adaxial leaf surface, strigose abaxial leaf surfaces, bearing ca. 12-14 nerves, the outer 2 staminate bracts abaxially longitudinally 5-ribbed and short coniculate below apex (Wang 1995).

Elatostema malipoense
Ecology. Elatostema malipoense is a scattered understory herb growing in moist clay soils in shady sites or near ravines at an altitude of ca. 1600 m, associated with Pilea insolens and some species of Ficus.
Distribution and conversation status. Elatostema malipoense is an endemic species and has only been collected from the type locality around Xiajinchang village Yunling, Malipo county, Yunnan, where a population of ca. 200 individuals was observed in an area of 1 km 2 . According to IUCN red list criteria (IUCN 2011), this new species should be classified as critically endangered (CR B2ab (iii); C2b). Similar species. Elatostema malipoense is a member of sect. Elatostema (Wang 2011a). In having penninerved leaves and a pistillate capitulum with numerous corniculate involucral bracts, E. malipoense resembles E. pseudobrachyodontum W.T.Wang. Elatostema pseudobrachyodontum differs from E. malipoense in having short-puberulous adaxial surface of the leaf blade, glabrous pistillate receptacles, pistillate bracts 1.5-2 mm long, and corniculate, pistillate bracteoles are green, 0.3-0.6 mm long, apex short-ciliate at the apex and achenes that are longitudinally 4-ribbed (Wang 1995).
Etymology. The species epithet 'malipoense' is derived from the name of the type locality, Malipo County, Yunnan Province, China.