Elatostema heterocladum W.T. Wang, A.K. Monro & Y.G. Wei, 2013

Wei, Yi-Gang, Monro, A. K. & Wang, Wen-Tsai, 2013, Additions to the Flora of China: three new species of Elatostema (Urticaceae) from Guangxi, Phytotaxa 147 (1), pp. 1-12 : 7-10

Elatostema heterocladum W.T. Wang, A.K. Monro & Y.G. Wei , sp. nov. ( Fig. 5 , A–G)

Most similar to E. androstachyum from which it can be distinguished by the stems maroon without scales; the inflorescence subtended by broad-ovate, staminate bracts two classes, major bracts 2, apex corniculate, minor bracts 4–6, with a truncate, erose apex and pistillate bracts ca. 6, with a cucullate apex, glabrous. Also most similar to E. luxiense from which it can be distinguished by the stems lacking small irregularly shaped brown scales, the possession of dwarf staminate stems which bear leaves that are strongly reduced in size and which lack cystoliths; the inflorescence subtended by broad-ovate bracts and staminate flowers subtended by linear bracteoles.

Type: — CHINA. Guangxi: Longlin county Dahongbao nature reserve , N 24°57′ 44" E105°09′35″, 1150 m, 27 March 2009, Y. G. Wei g086, (holotype PE!, isotype IBK!, BM!). Figure 6A–C .

Perennial herb, terrestrial, dioecious. Not tuber forming. Stems ca. 240–300 x 2.0– 2.5 mm, decumbent, maroon when fresh, branched, glabrous, internodes 5–9 mm. Stipules 2 at each node, caducous, 1.5–1.8 × 0.2–1 mm, narrowly linear, glabrous. Leaves distichous, alternate, the terminal pair of leaves subopposite, subsequent leaves subequal, petioles 0.5–1.5 mm, glabrous; laminae 50–140 × 20–44 mm, length: width ratio 1.5–3.18:1, asymmetrical, elliptic or oblong, chartaceous, 3-plinerved, the secondary nerves 2- 4, 60–90° to the midrib; upper surface drying dark green, glabrous, cystoliths densely or sparsely scattered, inconspicuous, bacilliform, 0.10–0.25 mm; lower surface drying brown-yellow, glabrous, cystoliths absent; base asymmetrical, cordiform/cuneate or obtuse/cuneate; margin serrate, the teeth spaced 5–9 mm apart; apex acuminate to caudate. Staminate and pistillate inflorescences borne on separate stems, modified staminate inflorescence bearing stems decumbent, simple or branched, with degenerate sessile or short petiolate leaves, 5–27 × 1.5–5 mm, oblong–linear, 1-nerved, cystoliths absent. Staminate inflorescences solitary, borne on modified stems, axillary, bearing 15–25 flowers in a pedunculate receptacle; peduncle 9–25 mm, glabrous, ebracteate?; receptacle 8–11 x 3–6 mm, discoid, not lobed, brown-yellow above, brown-yellow below, glabrous, subtended by marginal bracts, the bracts unequal, major bracts 2, borne opposite each other, at two sides of the receptacle, 3.8–5.0 × 2.4–4 mm, not erect, broadly ovate with a cucullate apex, the point of the apex corniculate, minor bracts 4-6, erect, 1.8–2.2 × 2.4-4 mm, broadly ovate with a truncate, erose apex. Staminate flowers ca. 5.0 x 3.0 mm at anthesis, white, pedicellate; pedicel ca. 2 mm, glabrous; bracteoles 2, unequal, major bracteole ca. 4.2 mm, linear, glabrous, minor bracteole ca. 2.0 mm, linear, glabrous; tepals 4, 3 × 1 mm, obovate-oblong, fused and connate towards the base, pale green, the subapical appendage 0.5-0.6 mm, corniculate, glabrous, stamens 4. Pistillate inflorescences axillary, solitary, pedunculate; peduncle ca. 0.6 mm, glabrous, ebracteate?; receptacle 2 mm in diameter, oblong, brown above, brown below, subtended by marginal bracts, the bracts equal, ca. 6, erect, broadly ovate with a cucullate apex terminating in a corniculate appendage, glabrous. Pistillate flowers immature; bracteoles 2 per flower, unequal, major bracteole 0.4 mm, broadly ovate, apically corniculate, glabrous or sparsely pubescent, where pubescent the hairs ca. 0.1 mm, minor bracteole 0.3 mm, broadly ovate. Infructescences not seen.

Distribution and ecology: Elatostema heterocladum is known only from the type locality growing on limestone hillsides in the shade of small trees and shrubs in disturbed vegetation. Mean annual rainfall at the type locality is ca 1100 mm. Ca. 90 individuals were seen growing in a single cluster.

Etymology: Elatostema heterocladum is named after staminate inflorescences borne on specialised stems which differ from those on which pistillate inflorescences are borne.

Vernacular name: Chinese (Mandarin): yijing louticao, meaning ‘different stem’, a reference to there being a modified staminate stem contrasting to a normally developed pistillate stem.

Discussion: Elatostema heterocladum may be easily distinguished from many other species in the genus, including those cited as most similar below by the delicate staminate inflorescence-bearing stems that bear greatly reduced leaves together with the discoid staminate receptacle. E. heterocladum is most similar to E. androstachyum and E. luxiense Wang (1982: 18) . It can be distinguished from E. androstachyum by stem, solitary staminate inflorescence, staminate bract and pistillate bract morphology as summarized in Table 3. It can be distinguished from E. luxiense W.T. Wang by leaf morphology and staminate inflorescence morphology as summarized in Table 4.

Conservation status:—A Global Conservation Assessment is presented here based on IUCN methodology (2001, version 3.1). Elatostema heterocladum is known from a single locality (criteria D2) where the population numbers ca 90 mature individuals (criteria D1 = <250). Plausible future threats that could drive this taxon to Critically Endangered or Extinct in a very short time are mining or conversion to agriculture of the limestone hills on which this species grow. Using the IUCN methodology the Global Conservation Assessment for E. heterocladum would be Critically Endangered (EN) according to criteria D. Much of the plant diversity of limestone karsts of Guangxi has been poorly documented and so it may be that future exploration and collecting in the area will encounter further populations. For this reason we downgrade the assessment to Vulnerable (VU) based on criteria D1 and D2.

Figures

FIGURE 5, A–F. Elatostema heterocladum W.T. Wang, Y.G. Wei & A. Monro: A, Staminate stem and pistillate stem; B, Staminate inflorescence; C, Staminate bracteoles; D, Young pistillate inflorescence; E, Pistillate bract; F, Two pistillate bracteoles; G, Staminate bract. (A–F Illustration by Ying-Bao Sun from holotype; G Illustration by Fang Wen from isotype).

FIGURE 6, A–C. Elatostema heterocladum W.T. Wang, Y.G. Wei & A. Monro: A, Habit and staminate inflorescences; B, Young pistillate inflorescence; C, Staminate inflorescences showing bracts, flowers and anthers. (A–C by Yi-Gang Wei from the isotype).