China. Yunnan, Hekou county, Nanxi village, Sanchahe river, 22°41'4"N, 103°59'26"E, 388 m, 01 Aug. 2010, Z. Y. Wu 10181 (Holotype: PE!; Isotype: PE!); the same locality, 01 Aug. 2010, Z. Y. Wu 10186 (Paratype: KUN!).

Perennial herb. Stems erect, 30-50 cm tall, glabrous, unbranched. Stipules narrowly lanceolate or lanceolate, 5–14 × 1.5–3 mm, with cystoliths 0.5–0.7 mm long, apex pungent; leaves shortly petiolate, glabrous, petioles 3–17 mm long; leaf blade chartaceous, obliquely narrowly ovate, broadly oblong or elliptic, 10–20 × 4.5–7.2 cm, glabrous, adaxial surface with 1 broad, interrupted, white stripe along the mid vein, adaxial surface with dense cystoliths, conspicuous, bacilliform, 0.25–0.8 mm long, penninerved, narrow side with (4-) 7–10 lateral nerves, broad side with (5-) 7–11 lateral nerves, base obliquely cuneate, margin denticulate, apex acuminate, shortly acuminate or obtuse. Staminate capitula solitarily axillary, glabrous; peduncle ca. 1.5 mm long; receptacle broadly oblong, ca. 8 × 6 mm; bracts 6, 2-seriate, ovate or narrowly ovate, abaxially above longitudinally 1-ribbed, with rib apex extended into subulate horn-like projections, outer 2 opposite, larger, 4–5 × 9 mm, with apex projection 3 mm long, inner 4 smaller, 4–5 × 5–7 mm, apex projection 1–1.5 mm long; bracteoles membranous, numerous, semihyaline, above brownish, obtrapezoid or navicular, 2–3.2 × 0.6–2 mm, above slightly conduplicate, apex cucullate. Staminate flower buds subsessile, broadly obovoid, ca. 2 mm long, glabrous, apex 4-corniculate. Female flowers and achenes not known.

Elatostema pleiophlebium is a forest understory herb. In the type locality, it occurs on wet ground in forest close to a river where it is associated with Elatostema alnifolium and some species of Musa, Ficus andPiperaceae.

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 km2. 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).

Elatostema pleiophlebium is a member of series Nanchuanensia W.T.Wang in sect. Elatostema (Wang 2011a). Elatostema pleiophlebium is similar to Elatostema quinquecostatum W.T.Wang in having numerous lateral leaf nerves and a staminate capitulum involucre formed of six glabrous bracts. Elatostema quinquecostatum differs from Elatostema 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).

The epithet ‘pleiophlebium' refers to the numerous lateral nerves characteristic of the leaves of this species.

China. Yunnan, Malipo county, Xiajinchang village Yunling, 23°10'6"N, 104°49'50"E, 1613 m, 05 Aug. 2010, Z. Y. Wu 10347 (Holotype: PE!; Isotype: KUN!).

Perennial herb. Stems erect, 30-50 cm tall, above sparsely short- puberulous near the node, unbranched. Stipules subulate or narrowly triangular, 0.1–0.2 mm long; leaves shortly petiolate, glabrous, petioles 1–6 mm long; leaf blade subchartaceous, obliquely oblong or narrowly obovate-oblong, 11–15 × 3–3.5 cm, both surfaces densely short strigose, cystoliths conspicuous, dense, bacilliform, 0.1–0.2 mm long, penninerved, lateral nerves 5–7-paired, base obliquely cuneate, apex cuspidate (entire), margin denticulate. Pistillate capitula solitarily axillary; peduncle ca. 8 mm long, short-puberulous; receptacle subquadrate or broadly oblong, 10–15 × 10–15 mm, 4-lobulate or irregularly 4–6-lobulate, short-puberulous; bracts ca. 75, deltoid or depressed-deltoid, 0.5–0.6 × 0.5–0.7 mm, ciliate, abaxial surface short-puberulous, apex with a subulate horn-like projections, 0.7–1 mm long; bracteoles membranous, whitish, semihyaline, narrowly obovate or oblanceolate, 0.5–1 mm long, apically long ciliate. Pistillate flower subsessile, tepals absent; pistil 0.8 mm long, ovary green, 3.5 mm long, stigma penicillate, ca. 4.5 mm long. Achenes ovoid, 0.6–0.7 × 0.4 mm, densely tuberculate. Staminate capitula not seen.

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.

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 km2. According to IUCN red list criteria (IUCN 2011), this new species should be classified as critically endangered (CR B2ab (iii); C2b).

Elatostema malipoense is a member of sect. Elatostema (Wang 2011a). In having penninerved leaves and a pistillate capitulum with numerous corniculate involucral bracts, Elatostema malipoense resembles Elatostema pseudobrachyodontum W.T.Wang. Elatostema pseudobrachyodontum differs from Elatostema 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).

The species epithet ‘malipoense' is derived from the name of the type locality, Malipo County, Yunnan Province, China.