Elatostema lui W. T. Wang, Y. G. Wei & A. K. Monro 2011, sp. nov.

Elatostema lui W.T.Wang, Y.G.Wei & A.K.Monro, sp. nov. (Fig. 6 & 7)

Elatostemo platycerati similis sed caulibus minoribus decumbentibus, foliorum lamina super sparse pubescenti, bracteus receptaculi staminalis principalis inconspicua, differt.

Type:— CHINA. Guangxi: cliff wall of gorge close to waterfall, N 23°00'53.8" E 106° 39'39.2", 350 m, 18 May 2010, A. K. Monro, Y. G. Wei & S. N. Lu 6781 (holotype IBK, isotypes BM, MO, PE).

Perennial herb, epipetric, dioecious? Not tuber forming. Stems 200–300 × 1–2 mm, decumbent, subsucculent, green, drying smooth or weakly sulcate, densely pubescent, 0.5 mm, weakly curved, strongly appressed, ascendent, internodes 10–46 mm. Stipules 2, interpetiolar at each node, caducous, internodes 9–13 mm, oblanceolate, glabrous. Leaves distichous, alternate, subequal, the major leaves petiolate becoming subsessile towards the apex, petioles 1.00–1.75 × 1.00– 1.75 mm, pubescent, 0.5 mm, weakly curved, strongly appressed, ascendent; the major laminae 36–132 × 20–40 mm, length:width ratio 1:2.3–3.6, symmetrical to weakly asymmetrical, obovate, membranous, 3-nerved, the secondary nerves 4–6 pairs, 45° to the midrib; upper surface drying very dark grey-green, sparsely pubescent, the hairs 0.75–1.00 mm, weakly curved, appressed, ascendent, cystoliths mostly absent, on primary and secondary veins, bacilliform, 0.25 mm; lower surface drying very dark grey-green, pubescent, the hairs 0.5 mm, weakly curved, appressed, ascendent, cystoliths on all veins, parallel to veins, bacilliform, 0.250 –0.375; base asymmetrical, cuneate/obtuse or obtuse/decurrent; margins serrate, basal ≤1/4 entire, the teeth 4.5–7.0 mm; apex acuminate to subcaudate. Staminate and pistillate inflorescences not borne on the same stems. Staminate inflorescences solitary, 5–7 mm, bearing 8–16 flowers in a pedunculate receptacle; peduncle 1.75–2.00 × 1 mm, pubescent, subtended by bracts; bracts 0.5–1.5 mm, deltate; receptacle 4–5 × 8–11 mm, suborbicular, not lobed or inconspicuously so, glabrous, green and black, drying black above, green drying black below, subtended by marginal bracts, bracts borne perpendicular to the receptacle, the bracts unequal, major bract 1, 6 mm, 9–lobed, the lobes auriculate, green, minor bracts 20, 3.5–4.0 mm, obtuse deltate, black. Staminate flowers 1.5 × 1.5 mm immediately prior to anthesis, white, pedciellate, bracteolate; pedicel 1.5–2.0 mm, glabrous; bracteoles 2, equal, 2.5–3.0 mm, obovate or elliptic; tepals 4, the subapical appendage 0.25–0.50 mm, corniculate. Pistillate inflorescence solitary, 2–3 mm, bearing 60–120 flowers in a pedunculate receptacle; peduncle 1.0–1.5 × 1 mm, glabrous, bracteate; bracts 0.50–0.75 mm, deltate; receptacle 2 × 4–5 mm, subquadrate, not lobed, sparsely pubescent, green, drying near black above, green, drying near black below, subtended by marginal bracts, the bracts unequal, green, drying dark grey-green to black, major bracts 2, 2.5–3.0 mm, corniculate, minor bracts 4, 2.5 mm, auriculate, subminor bracts 18, 2 mm, deltate and corniculate. Pistillate flowers not seen. Infructescence, pedicellate; pedicel 0.25 mm; bracteoles 2, equal, 0.75–1.25 mm, oblanceolate or narrow deltate; achenes 60– 120 per infructescence, 0.75 × 0.375 mm, narrowly ovoid, pale brown.

Distribution:—Known only from the type locality, the Gulong gorge in Jingxi County, Guangxi, Southwest China at an elevation of ca 350 m. This species is epipetric, growing on limestone cliffs in relatively shaded humid conditions close to the river’s edge.

Etymology:—This species is named after Shi Nian Lu, an amateur botanist who has shown us many interesting localities and interesting plants.

Discussion:— Elatostema lui is most similar to Elatostema platyceras Wang (1988) from which it can be distinguished based on stem, leaf and staminate inflorescence and flower morphology as summarised in the table below:

Conservation status:—A Global Conservation Assessment is presented here based on IUCN methodology (2001, version 3.1). Elatostema lui is known from a single locality (IUCN criteria D2). This locality is a gorge ca 4 km in length running through relatively undisturbed vegetation that was logged in the 1950s. The species was relatively common at the locality but the population is likely to number less than 500 mature individuals (IUCN criteria D1). Using the IUCN methodology our Global Conservation Assessment for Elatostema lui is Vulnerable (VU) based on criteria D1 and D2: population size and number of locations combined with a plausible future threat that could drive this taxon to Critically Endangered or Extinct in a very short time. Future threats include damming of the Gulong River for irrigation or hydroelectricity generation, local tourism or mining.

Figure 6. Elatostema lui. A. Habit with stipules and staminate inflorescences visible. B. Staminate inflorescence viewed from the side with receptacle bracts visible. C. Stipule. D. Achene with bracteole. E. Staminate flower with bracteole. Monro, Wei & Lu 6781, IBK (Illustration by Sun Ying-Bao & Ruth Harker).