Boehmeria polystachya 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 : 127-129

13. Boehmeria polystachya Wedd. — Fig. 11 ; Map 14

Boehmeria polystachya Wedd. (1856) 370. ― Type: Wallich 4584 (holo K-WALL; iso G, K), Nepal.

Boehmeria tibetica C.J.Chen in Wang & Chen (1979) 109. ― Type: Chinghai­ Tibet exped. 2775 (holo PE), China, Tibet, Tsona , 4 Oct. 1974.

Urtica venosa Wall. (1831) 164, nom. nud. – See Note 1.

Robust herb or subshrub, up to 1.5 m tall; ultimate branches at extreme apex 1–1.5(–2) mm diam, but soon becoming very robust, hairy, hairs sparse or dense fine short adpressed, soon glabrescent. Stipules linear-lanceolate rather thin-textured ± membranous, 7–10 by 1–2 mm. Leaves opposite, not or very slightly dimorphic in size only, ovate, medium or large, (8–)11–23 by (4–) 6–12 cm, little-varying in relative proportions with length usually c. 2 × width; margin sometimes crenate, usually serrate or dentate, teeth acute or obtuse, often slightly up-curved, 30– 55 either side, varying in number and size depending on lamina size, 1–1.5 by 2–4.5 mm; leaf apex short-attenuate; base slightly asymmetrically rounded to slightly cuneate or cordate; basal veins extending into distal half of leaf, upper lateral veins 3 –5 subopposite, lowermost usually arising in distal half, finely impressed adaxially, robust and prominent abaxially; coarser tertiary veins close-spaced scalariform (0.3–0.5 cm apart, up to 1 cm apart in largest leaves) and very prominent abaxially, especially those arising from outer side of basal veins, giving a very ridged appearance to young leaves; fine reticulation often also relatively prominent; texture thin- or thick-chartaceous; adaxial surface drying markedly dark, hairy, hairs sparse (rarely abundant), very fine, adpressed, cystoliths abundant but minute; abaxial surface rather paler green in both living and dry state, hairs often restricted to veins, sparse (rarely abundant), extremely fine, adpressed; petiole usually c. 0.25 × lamina length. Flower­clusters borne on leafless axes, these fairly long, pendulous or drooping, 10–17 cm long, arising one from each axil with many much shorter lateral branches throughout length which are also branched (i.e., inflorescence-bearing axes with 2nd-order branching), axes unisexual or bisexual (female clusters in apical part; entirely female axes also generally towards branch apex); bracts short, ovate-triangular, thick-textured, 1–1.5 by 0.5–0.8 mm; flower-clusters spaced 2–4 mm apart, recorded as dark crimson, small, 2 – 3 mm diam, flowers in male clusters 5–10, in female clusters 20–30(–40), densely crowded; bracteoles oblong, inconspicuous, 0.2–0.3 mm long. Male flowers 4-merous, sessile, mature buds depressed-globose, 0.8–1 mm diam, without appendage or with slight dorsal thickening, hairy, hairs abundant, minute, spreading or adpressed. Female flowers narrowly oblong, c. 0.8 by 0.2 mm; stigma minute, 0.3–0.6 mm long, hooked. Fruiting perianth 1–1.5 by 0.5–0.8 mm, ellipsoid without distinct beak, markedly flattened either side of achene into distinct wing either side comprising 0.25(–0.3) × whole width; hairs minute, spreading. Achene in central part of fruiting perianth, occupying less than half of it.

Distribution ― Eastern Himalayas: north-eastern India (Sikkim, Assam, Meghalaya, Uttarakhand), Nepal, Bhutan, Burma, China (Tibet border region with India).

Habitat & Ecology ― Mixed broad-leaved deciduous forest, forest margins, scrub, open slopes, walls and banks in disturbed ground; 1300–3300 m altitude.

Conservation status ― Least Concern (LC). The species is known from at c. 50 collections, some of which are recent. It occurs in many scattered locations and in fairly restricted forest habitat. The EOO is 284 285 km 2. Although the AOO gives a figure of less than 500 km 2, its localities in the Himalayas are not currently threatened by serious habitat degradation, and it therefore does not meet the criteria for a formal status of Vulnerable (VU).

Notes ― 1. The nomen nudum U. venosa , cited by Weddell (1856: 378) as a synonym under B. rugulosa , is referable to this species.

2. Distinctive in its leaves relatively large broadly-toothed with hairs very inconspicuous adpressed and tertiary veins scalariform closely-spaced prominent (giving a ridged appearance to young leaves), its inflorescence-bearing axes with short branches throughout length and with 2nd-order branching, tiny stigma and fruiting perianth broadly-winged.

3. The sympatric B. conica has been confused with this species but differs in its inflorescence-bearing axes small, neat and rather conical, its leaves thin-textured often truncate with slender veins and its fruiting perianth short and broad.

4. The partly sympatric B. siamensis with its very similar scalariform venation prominent close-spaced can also be confused with B. polystachya but differs in leaves often relatively narrower, petioles extremely short relative to lamina and bracts at the flower-clusters always conspicuous, longer than mature clusters and often almost as wide as long, inflorescence-bearing axes paired and unbranched.

5. Several sympatric varieties of B. virgata subsp. macrophylla have similar leaf shape to B. polystachya and branched inflorescence-bearing axes, especially var. scabrella and var. rotundifolia which have male axes much-branched throughout length (although always without 2nd-order branching) but venation is always finer and not conspicuously scalariform. Var. scabrella can also be distinguished by its hairs on stem and adaxial leaf surface conspicuous, coarse, rough and var. rotundifolia also by its leaves thinner-textured with a distinct abrupt acumen consisting of a single tooth and by its marginal teeth markedly up-curved especially near the leaf apex.

Figures

Map 14 Distribution of Boehmeria conica C.J.Chen, Wilmot-Dear & Friis (●), B. polystachya Wedd. (▲) and B. kurzii Hook.f. (ä).

Fig. 11 Boehmeria polystachya Wedd. a. Habit with branched, immature inflorescence-bearing axes; b. part of stem with branched, mature inflorescencebearing axes; c, d. leaves of different form (from different plants); e. detail of stem indumentum and stipule; f. detail of inflorescence-bearing axes with female and bisexual clusters (inflorescences); g. male bud; h. fruiting perianth (a: Gamble 906A; b: Gamble 7103; c, e: KEKE 897; d: Hooker & Thomson s.n.; f, g: Clarke 26736B; h: Clarke 26467C; all K). — Scale bars: a-d, f = 2 mm; e = 5 mm; g, h = 1 mm.