Boehmeria hamiltoniana Wedd.

Wilmot-Dear, C. M. & Friis, I., 2013, The Old World species of Boehmeria (Urticaceae, tribus Boehmerieae). A taxonomic revision, Blumea 58 (2), pp. 85-216 : 125-127

12. Boehmeria hamiltoniana Wedd. — Fig. 10k–n ; Map 13

Boehmeria hamiltoniana Wedd.(1856) 371. ― Boehmeria platyphylla D.Don var. hamiltoniana (Wedd.) Wedd. (1869) 213. ― Type: Wallich 4590 (holo K-WALL), Nepal, 1821.

Boehmeria ingjiangensis W.T. Wang (1981b) 414,syn. nov. ― Type: G.D. Tao 13627 (holo KUN), China, Yunnan, Ingjiang, 4 Oct. 1974.

Shrub, up to 5 m tall; ultimate branches fairly slender, 0.8–1.2 mm diam, glabrous or with sparse fine hairs near apex, soon glabrescent. Stipules very narrowly triangular, 7 by 1.5 mm, robust, glabrescent, soon deciduous. Leaves opposite, slightly dimorphic in size and shape with ‘larger’ leaves c. 1.5 × length of ‘smaller’ leaves; asymmetrical or not, narrowly ovate-attenuate, fairly long, (6–)12–20 by (1.5–) 2–4.5 cm, length 3–6 × width; margin irregularly and often indistinctly serrate (rarely largest leaves crenate), teeth 20–30(–40) either side, shallow, 0.5–1 by (1.5–) 2–5 mm, their upper margin convex; leaf apex gradually tapering long-attenuate and sometimes slightly sideways-curved; base short-cuneate; basal veins usually extending almost to tip, upper lateral veins rather indistinct, unequally arranged 1–2 on one side with both arising near tip and 2(–3) on other side with lowermost arising in distal third or rarely near middle of lamina; venation inconspicuous adaxially, basal veins finely prominent abaxially, coarser tertiary venation somewhat scalariform often visible abaxially; texture membranous or very thin-chartaceous, drying light or deep dark green; adaxial surface glabrous and almost shiny with many prominent cystoliths; abaxial surface glabrous or with hairs on veins, these very sparse, adpressed; petiole 5–6 cm long, very variable, relative to lamina, often more than half of lamina length. Flower­clusters borne on leafless axes, these 1–several from each axil and each axis often forked once or twice near base, male inflorescence-bearing axes 4–9 cm long in lower axils, female ones ± pendulous, (7–) 10–20 cm long in upper axils, some axes with both sexes; clusters very crowded almost contiguous or spaced, up to 5 mm apart, male clusters 2–4(–5) mm diam, with c. 3–10 crowded flowers; female clusters 1.5–3 mm diam, with 15–30(–more than 50) flowers; bracts broadly triangular but minute, 0.5–0.8 mm long. Male flowers 4-merous, sessile, mature buds globose and slightly depressed, relatively large, 1.5 mm diam, tepals with prominent dorsal appendage, glabrous or very sparsely adpressed-hairy. Female flowers up to 0.8 mm long, sparsely fine-hairy; stigma only 0.7–0.8(–1) mm (– 1.2 mm in Thailand). Fruiting perianth only 0.6–1 by 0.3–0.4 mm, ellipsoid or obovoid, somewhat laterally flattened with marginal rim becoming ± wing-like in distal part, (sparsely-) abundantly hairy, hairs spreading, usually very short. Achene filling most of fruiting perianth.

Distribution ― Eastern Himalayas: north-eastern India (Sikkim, Meghalaya, Arunachal Pradesh, Nagaland), Nepal, Bangladesh, Bhutan, Burma, southern China, northern Thailand.The single record from Indonesia (Jawa) is presumed introduced, see discussion in Note 1.

Habitat & Ecology ― Steep valleys in subtropical forest, gallery forest, open limestone outcrops in mixed forest; 800– 2000 m altitude.

Conservation status ― Near Threatened (NT). The species is known from c. 50 collections, some of which are recent, with an estimated EOO of 962 172 km 2, but an AOO of less than 500 km 2. It occurs in many scattered locations and in fairly restricted forest habitat. Although the habitats in many of its localities are not currently threatened by serious degradation, and it therefore does not meet the criteria for a formal status of Vulnerable (VU), it may become so in the future with increasing agriculture in these regions.

Notes ― 1. The record from Jawa is probably an accidental introduction, since the collection ( Van Harreveld 6665 (L)) states “Experimental station of the Javanese sugar industry”. It has therefore not been mapped or included in the assessment of conservation status.

2. Distinctive in its leaves membranous, long-attenuate, drying consistently light or dark green, often glabrous and/or only indistinctly toothed, with basal veins long and upper veins few, inconspicuous, its inflorescence-bearing axes often dichotomously forked at the extreme base, the males axes short and slender with few-flowered clusters, and its fruiting perianth small, relatively broad with width often almost equalling length. It is otherwise rather similar to the partly sympatric ( China) B. densiflora which differs in leaves mostly thicker-textured with fine adpressed hairs adaxially and tepals of male flowers without dorsal appendages.

3. The sympatric but rare B. leptostachya has been misidentified as this species, having leaves thin-textured with inconspicuous veins but differing in its leaves shorter, wider, broadertoothed, shiny and distinctly minute-hairy adaxially, drying consistently brownish black with veins, petioles and inflorescence-bearing axes all distinctly red-tinged, and its flower-clusters well-spaced with few flowers.

4. The partly sympatric B. lanceolata also has similar venation but leaves obovate, thicker-textured, relatively wider, stem fine-hairy and female inflorescence-bearing axes erect.

5. Boehmeria zollingeriana var. blinii has somewhat similar leaves but drying markedly brownish black with upper veins more numerous and conspicuous; fertile material is easy to distinguish, with male flowers long-pedicellate and in simple axillary clusters and female inflorescence-bearing axes often branched.

Figures

Map 13 Distribution of Boehmeria hammiltoniana Wedd. (▲) and B. lanceolata Ridl. (●).

Fig. 10 a–j: Boehmeria lanceolata Ridl. a. Habit, upper part of stem with inflorescence-bearing axes; b. leaf; c. detail of leaf apex; d. stipule; e. detail of male inflorescence-bearing axis showing one cluster (inflorescence); f. detail of female inflorescence-bearing axis showing one cluster (inflorescence); g–j. fruit- ing perianths of different form (from same plant: g, h. unribbed; i. four-angled; j. fruiting perianth with marginal rim). — k–n: Boehmeria hamiltoniana Wedd. k. Leaf; l. detail of leaf margin; m. detail of male inflorescence-bearing axis showing one cluster (inflorescence); n. fruiting perianth (a–f: Hiep 130; g–j: Tsang 30455; k, l: Gamble 7291; m, n: Clarke 27246; all K). — Scale bars: a, b, k = 2 cm; c, e-j, m, n = 1 mm; d, l = 2 mm.