Boehmeria ternifolia D.Don

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 : 175-177

24. Boehmeria ternifolia D.Don — Fig. 30 ; Map 31

Boehmeria ternifolia D. Don (1825) 59. ― Type: Hamilton s.n. (holo BM), Nepal.

Subshrub, shrub or small tree, 0.5–4.5 m. Stems with hairs abundant to very dense, minute (≤ 0.3 mm long), fine, soft, spreading, brown. Stipules long and narrow, 8–9 by 1–2 mm, densely hairy outside like the stem. Leaves scarcely or markedly dimorphic in size with length of ‘larger’ 1–1.5(–2) × ‘smaller’ ones, very broadly elliptic or deltate, rarely obovate-obdeltate or rhombic-ovate to ovate-truncate, slightly or moderately asymmetrical, widely varying in size (4–)7–14(–20) by (3–)7–13.5(–16) cm excluding apical tooth (see below), length 0.8–1.25 × width; margin dentate or sometimes ± crenate with 7–20(–25) teeth either side, these up-curved with a wide size range on different plants, small to large, (1.5–)2–6 by 4–11 mm, length 1.25–4 × width, all ± uniform or distal ones progressively larger, also usually increasingly up-curved with the pair of teeth either side of the apex often markedly in-curved; leaf apex either with 2 – 3 lobes of ± equal length giving truncate outline to apex, or abruptly terminated by a terminal tooth which is long, narrow ± linear and tail-like; base often ± oblique, very broadly cuneate or ± truncate with cordate extreme base, sometimes broadly rounded to ± cordate; texture thin-chartaceous or (mostly in Nepal) membranous; leaves recorded as greenish purple in live state; adaxial surface with hairs sparse or fairly abundant, fine, half-adpressed or spreading, soft, bulbous-based; abaxial surface velvety with hairs ± spreading denser and finer (not bulbous-based), rarely on veins only, often whole surface densely hairy. Flower­clusters on leafless inflorescence-bearing axes, these pendulous slender, unisexual but often on same stem with male axes in lower leaf axils; male axes 4–15 cm, unbranched or more often with several branches at or close to base; female axes 10–20(–30) cm, rarely branched; clusters on both male and female axes spaced 1–2 mm apart or contiguous, female clusters 3–4 mm diam in fruit, with bracts often conspicuous up to 1 mm long but soon caducous from female clusters. Male flowers 4-merous, ± sessile, mature buds c. 1.5 mm diam, globose, tepals with dorsal appendage. Fruiting perianth ellipsoid or obovoid, without or with very slight beak, with distinct marginal rim or occasionally ± winged, ± rounded, rarely slightly tapering at base, 1–1.5(–2) by 0.6–0.8 mm, densely minute-hairy.

Distribution ― Eastern and western Himalayas:northern India, Nepal, Bhutan.

Habitat & Ecology ― Dense montane forest, forest clearings and margins, often in damp shady ravines or by waterfalls; 1000–2300 m altitude.

Conservation status ― Least Concern (LC). It is known from over 50 collections from many locations along the Himalayas. It occurs in fairly restricted forest habitat, but is probably not at risk since these localities in the Himalayas are not threatened by serious habitat degradation. Separate formal assessments are not considered meaningful for the two intergrading varieties.

Notes ― 1. This species is a small shrub distinctive in the appearance of its marginal teeth and in its abundant minute spreading brown stem indumentum (often also dense on most parts of plant) and in its leaf shape and marginal teeth which distinguish the two varieties from one another. It is restricted to the southern foothills of the Himalayas from Garhwal and Kumaon to Bhutan (and possibly extending into Burma).

2. The typical variety is distinctive in its leaves with an abrupt long single terminal tooth which may be long-triangular but is often very narrow ± linear ‘tail-like’ and constricted at its base and is usually much longer than marginal teeth (a character otherwise seen only in B. virgata subsp. macrophylla var. rotundifolia , which differs as discussed below, see Note 5). The marginal teeth of var. ternifolia are sometimes ± uniform along most of margin but usually distinctive in distal ones being progressively wider (but scarcely longer) than proximal ones, often markedly so, also usually progressively more up-curved (even if proximal ones are out-pointing and rounded) and the uppermost pair often markedly in-curved towards the terminal tooth, giving a distinctive claw-like appearance to the leaf apex.

3. In the eastern part of its range var. ternifolia merges gradually via a range of intermediate forms into var. kamley whose leaves are often less densely hairy and have fewer marginal teeth, distal ones progressively markedly larger (both longer and wider) and leaf apex with 2–3 large broad apical teeth or lobes rather than a single tail-like tooth. The two variants of B. ternifolia are recognised only at varietal level because of the range of intermediates. Leaf form in the species changes from west to east with some material from Nepal and Sikkim being impossible to assign to either variety, while further west all conforms to var. ternifolia and almost all from Bhutan and some from Sikkim conforms to var. kamley .

4. The allopatric B. japonica is also characterised by change in form of marginal teeth towards leaf apex, its distal teeth markedly longer as well as wider. It would not easily be confused with var. ternifolia (which has distal teeth scarcely longer), but broad-leaved apically 3-toothed variants of B. japonica var. japonica are almost identical in leaf shape to var. kamley . Boehmeria japonica is distinguished by unbranched herbaceous (rather than branched shrubby) habit, adaxial leaf-hairs coarse and stiff (rather than fine and soft) and male tepals without a dorsal appendage. The cytological work of Acharya (in Acharya et al. 2003) shows var. kamley to be diploid and sexually reproducing whereas Okabe (1956) and Yahara (1983a, 1984a) demonstrated (as discussed in the introduction) that B. japonica comprises a polyploid complex of partly apomictic and partly hybridising entities. This indicates that hybridisation between these two neighbouring but allopatric taxa has not occurred despite the remarkably intermediate appearance of var. kamley and its occurrence where the distribution of B. ternifolia is least far from that of B. japonica . This is a good example of the way cytological information can clarify relationships where taxa are similar in gross morphology.

5. Boehmeria ternifolia var. ternifolia can be confused with certain Himalayan varieties of the very variable B. virgata subsp. macrophylla . Var. rotundifolia is the most similar with a tail-like terminal tooth and increasingly up-curved marginal teeth but is distinguished by its stem hairs closely-adpressed rather than spreading (sometimes longer (c. 1 mm long) curved hairs also present), its marginal teeth often more numerous and its inflorescence-bearing axes (especially the male ones) erect and often branched throughout length; it is also a herb rather than a shrub, occurring in more open habitat at higher altitude. Himalayan forms of the very variable subsp. macrophylla var. macrostachya can also be somewhat similar to B. ternifolia but never have a distinctive basal constriction to the terminal tooth nor distal marginal teeth progressively wider nor uppermost teeth in-curved, and these particular Himalayan forms are also distinguished by smaller more numerous teeth. Subsp. macrophylla var. strigosa (allopatric, China and Indochina) can also have an abrupt tail-like leaf apex but would not be confused with B. ternifolia , differing markedly in closely-adpressed ± silky indumentum on stem and leaves.

6. Forms of var. ternifolia with fairly uniform teeth and dense indumentum are easily confused with the sympatric but more widespread B. ourantha which also has dense soft indumentum. The clearest distinguishing character of B. ourantha is its unusual inflorescence architecture, with male flowers differently arranged, being mostly in a few clusters at the apex of a mainly female axis or scattered flowers in mainly female clusters; female and bisexual axes are always unbranched and mostly much more congested, and the apical tooth of leaves is never tail-like nor basally constricted; marginal teeth are mostly more numerous (more than 25) and distal ones not in-curved; indumentum is also longer, (0.5–) 1–2 mm long, (rather than ≤ 0.3 mm) and always dense on the abaxial surface of leaves.

7. Leaves of var. ternifolia with fairly uniform marginal teeth are also somewhat similar to those of B. holosericea but this species is allopatric (eastern Asia) and less likely to be confused with it, being a herb with marginal teeth wider than long (rather than length exceeding width) and with its leaf indumentum much longer than its stem indumentum (rather than both leaf and stem indumentum similar, very short).

Key to varieties

1. Leaf apex consisting of a single terminal tooth, long, linear tail-like; marginal teeth 12–25 in number, uniform or distal ones progressively wider but scarcely longer. — Eastern and western Himalayas............... a. var. ternifolia

Figures

Map 31 Distribution of Boehmeria ternifolia D.Don var. ternifolia (●) and B. ternifolia D.Don var. kamly (Acharya & Yonek.) Friis & Wilmot-Dear ().

Fig. 30 a–l: Boehmeria ternifolia D.Don var. ternifolia. a. Habit of stem with inflorescence-bearing axes; b. detail of stem showing basal branching of male inflorescence-bearing axes; c–e. leaves from different plants; f. leaf, detail of adaxial surface; g. leaf, detail of abaxial surface; h. detail of stem and stipules; i. male bud; j. detail of female inflorescence-bearing axis with two flower-clusters (inflorescences); k, l. fruiting perianths from different plants. — m, n: Boehmeria ternifolia var. kamley (Acharya & Yonek.) Friis & Wilmot-Dear. Leaves from different plants. — o: Intermediate between var. ternifolia and var. kamley. Leaf (a: Duthie 24955; b: Thomson 701; c, l: Gamble 7006; d: Gamble 26635; e-i: Wallich 1262; j, k: Grey­Wilson 271; m: Clarke 13029; n: Grierson 4161; o: Bourne s.n.; all K). — Scale bars: a, c-e, m–o = 2 cm; b, h, j = 2 mm; f, g, i, k, l = 1 mm.