Elatostema arcuatobracteatum L.F. Fu, V. T. Do & C.X. He, 2014

Fu, Long-Fei, Do, Van Truong, Wen, Fang & He, Cheng-Xin, 2014, Elatostema arcuatobracteatum (Urticaceae), a new species from Vietnam, Phytotaxa 174 (2), pp. 111-111 : 111

Elatostema arcuatobracteatum L.F. Fu, V. T. Do & C.X. He , sp. nov. ( Fig. 1 & 2 )

Most similar to Elatostema xanthophyllum from which it can be distinguished by the branching of the stem, pistillate bract and bracteole diameter and shape together with the presence of cystoliths.

Type:— VIETNAM. Ha Giang: Bac Me District, Bac Me Nature Reserve , 500 m, N 22.754167°, E 105.226667° ( WGS84 ). 16 June 2012, L. F . Fu , V. T . Do & F . Wen VMN_ CN219 (holotype VNMN!, isotypes IBK!) .

Perennial herb, terrestrial, dioecious. Not tuber forming. Stems 250–300 × 2.1–2.5 mm, erect, branched, green when fresh, with cystoliths, densely scattered, bacilliform, 0.5–1.0 mm, furfuraceous, glabrous, sulcate, internodes 9–30 mm; Stipules 2, interpetiolar at each node, lanceolate or lanceolate-triangular, persistent or caducous when inflorescences borne on this node, 8–18 × 2.0– 2.5 mm, with cystoliths, densely scattered, bacilliform, 0.3–0.5 mm, furfuraceous, apex puberulent. Leaves distichous, alternate, terminal pair of leaves subopposite, subsequent leaves subequal, short petiolate, petioles 2.5–8.0 mm, furfuraceous, glabrous; laminae 90–165 × 37–50 mm, length: width ratio 2.43–3.3:1, asymmetrically oblong, chartaceous, pinnately nerved, lateral veins 5–7 pairs, borne 45–60° to the midrib; upper surface drying yellow-green, glabrous, cystoliths densely scattered, bacilliform, 0.3–0.5 mm; lower surface drying brown-green, glabrous, cystoliths densely scattered, bacilliform, 0.3–0.5 mm; base asymmetrical, broader-half cuneate, rounded or auriculate, narrower-half cuneate; margin denticulate, the teeth spaced 6–15 mm apart, basal ≤1/3 entire; apex acuminate or long acuminate, entire. Staminate and pistillate inflorescences not borne on the same stems. Staminate inflorescences paired, axillary, capitate, bearing ca. 130 flowers in a pedunculate receptacle; peduncle ca. 1.0 × 2.2 mm, glabrous, ebracteate?; receptacle 16–19 × 8–10 mm, oblong, weakly divided into two lobes, yellow, with cystoliths below, cystoliths densely scattered, bacilliform, 0.3–0.5 mm, glabrous, subtended by marginal bracts; the bracts ca. 6, subequal, broadly ovate, abaxial surface with cystoliths, densely scattered, bacilliform, 0.3–0.5 mm. Staminate flowers 1.8–2.2 × 1.8–2.1 mm immediately prior to anthesis, pedicellate, bracteolate; pedicel ca. 1.1 mm, glabrous; bracteoles 2 per flower, equal, membranous, semitransparent, 0.9–1.3 × 0.3–0.4 mm, lanceolate or linear, apex pubescent, the hairs ca. 0.5 mm, abaxial surface with cystoliths, densely scattered, bacilliform, ca. 0.1 mm; tepals 5, broadly ovate, 0.9–1.2 × 1.0– 1.1 mm, subapical appendage ca. 0.5 mm, corniculate, pubescent, the hairs ca. 0.5 mm. Pistillate inflorescence paired, axillary, capitate, bearing ca. 50 flowers in a pedunculate receptacle; peduncle 2.0–5.5 × 0.8–1.2 mm, the junction of peduncle and receptacle with cystoliths, densely scattered, bacilliform, 0.3–0.5 mm, furfuraceous, glabrous, ebracteate?; receptacle subrounded, 7–9 mm in diam., weakly divided into two lobes, receptacle lower surface with cystoliths, densely scattered, bacilliform, 0.3–0.5 mm, glabrous, green, subtended by marginal bracts, the bracts 2, equal, arcuate, opposite to each other, 0.8–1.1 × 8–10 mm, abaxial surface with cystoliths, densely scattered, bacilliform, 0.3–0.5 mm. Pistillate flowers ca. 0.3 × 0.1 mm at anthesis, cream when fresh, pedicellate, bracteolate; pedicel ca. 0.25 mm; bracteoles 2 per flower, subequal, ca. 1.1 × 0.6 mm, ovate, apex cucullate, pubescent, abaxial surface with cystoliths, densely scattered, bacilliform, ca. 0.1 mm. Infructescences not seen.

Distribution:—Known only from the type locality in Bac Me Nature Reserve, Ha Giang Province, North Vietnam where Elatostema arcuatobracteatum is known growing in the shade of broad-leaved evergreen forest on limestone karst hillsides at an elevation of 500 m.

Etymology:— Elatostema arcuatobracteatum is named after the pistillate inflorescence with arcuate bract.

Vernacular name: VIETNAM: cao hùng lá bắc cung.

Discussion:—Species of Elatostema are difficult to distinguish due to their tiny flowers. Moreover, variation in staminate tepal number and the reduced nature of pistillate tepals reduce the number of characters available for species delimitation. Wang (2010) studied bract and bracteole morphology of Elatostema and concluded that their number, shape and size are constant within a species. Building on this conclusion we suggest that bract and bracteole morphology are more valuable for species classification in Elatostema than observing the flowers.

Elatostema arcuatobracteatum is unique amongst Vietnamese and Chinese Elatostema by its arcuate pistillate bract shape. Elatostema arcuatobracteatum is most similar to Elatostema xanthophyllum W.T. Wang (1982) from which it can be distinguished based on stem, pistillate bract and bracteole morphology as summarized in Table 1.

Conservation status:—A Global Conservation Assessment is presented here based on IUCN methodology (2001, version 3.1). Elatostema arcuatobracteatum is known from a single locality (IUCN criteria D2). At this locality the population of this species comprises ca. 350 individuals (IUCN criteria D1) growing in two populations within a nature reserve. Using the IUCN methodology the Conservation Assessment for E. arcuatobracteatum would be Vulnerable (VU), however no plausible threat could be found to confirm its status as the population is located within a protected area and not under threat in the near future, in addition, considering surrounding area has not been completely explored. For these reasons the Global Conservation Assessment for Elatostema arcuatobracteatum is Least Concern (LC).

Figures

FIGURE 1. Elatostema arcuatobracteatum. A. Habit with leaves, stipules and pistillate inflorescences visible. B. Staminate inflorescences from below with marginal receptacle bracts. C. Staminate bracteoles. D. Pistillate inflorescence viewed from below with marginal bracts visible. E. Pistillate bracteole. VMN_CN219, IBK (Illustration by Wen-Hong Lin).

FIGURE 2. Elatostema arcuatobracteatum. A. Habit. B. Staminate plant. C. Pistillate plant. D. Staminate inflorescences. E. Pistillate inflorescences. F. stipule. VMN_CN219 (Photo L.F. Fu).