Boehmeria leptostachya Friis & Wilmot-Dear

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 : 121-123

10. Boehmeria leptostachya Friis & Wilmot-Dear — Fig. 9 ; Map 12

Boehmeria leptostachya Friis & Wilmot-Dear in Wilmot-Dear et al. (2010) 441. ― Type: Geesink et al. 7428 (holo K; iso AAU, BKF, L, S), Thailand, Peninsula, Ranong, Khao Pawta Luang Keow , 22 June 1974.

Boehmeria erythropoda sensu Yahara (1981) 15, non Miq. – See Note 1.

Shrub, 2–4 m tall; ultimate branches 1–15 mm diam, glabrous drying red-brown. Stipules lanceolate 4–7 by 1–1.5 mm, rather thick-textured. Leaves opposite, very variably slightly or moderately dimorphic in size, with length of ‘larger’ leaves 1.3–1.7(–2.7) × ‘smaller’, ± symmetrical or with abaxial side slightly broader than adaxial, most leaves on most branches elliptic, often a few elliptic-ovate, medium to large, ‘larger’ 13–18 by 5–7 cm, length 2.1–2.8 × width; margin shallowly and broadly crenate to bluntly serrate, with 30– 35 teeth either visible throughout length or progressively shallower towards base and only discernible in distal 2/3 of margin, up to 0.7 by 5–8 mm; leaf apex short-attenuate to indistinctly or abruptly short-acuminate; base slightly asymmetrically short-cuneate; basal veins extending to distal third of lamina or on adaxial side almost to tip, upper lateral veins 2(–3), lowermost on adaxial side arising near middle of lamina, on adaxial side in distal third, slender inconspicuous adaxially, fine-prominent abaxially, coarser tertiary venation ± scalariform fine-prominent abaxially; texture membranous or very thin-chartaceous, both surfaces green when living but drying consistently dark brownish black adaxially and lighter brown abaxially with especially veins red-tinged, adaxial surface ± shiny (said to be sticky when live: Yahara 1981) with sparse hairs, these minute (<0.2 mm long), adpressed; abaxial surface with sparse hairs even smaller, finer, often ± spreading; petiole hairy as lamina, drying red-tinged, in ‘larger’ leaves relatively long, 0.3–0.5 × lamina length, in ‘smaller’ leaves much shorter (often only 0.1 × lamina length). Flower­clusters borne along leafless axes, these ± pendulous very slender, 10–50 cm long, unbranched; bracts minute, inconspicuous, 1–1.5 by 1 - 1.5 mm; clusters well-spaced, 2–more than 5 mm apart, most clusters with both sexes, clusters small, 1.5–2 mm diam, with up to 10(–15) flowers; bracteoles minute inconspicuous. Male flowers 4-merous; pedicels up to 0.5 mm long, mature buds depressed-globose, 1.2–1.5 mm diam, with conspicuous dorsal thickening on each lobe and sparse fine hairs like leaves. Female flowers up to 0.5 mm long, stigma often minute, down curved, 0.3–1.5 mm long. Fruiting perianth only 0.7–0.9 by 0.5–0.7 mm, very broadly ovoid or ellipsoid with minute beak, markedly dorsiventrally flattened with marginal ridge or narrow thick-textured wing, sparsely hairy, hairs short, ± spreading. Achene filling most of fruiting perianth.

Distribution ― Southern China, southern Thailand, Indonesia (Sumatera).

Habitat & Ecology ― Evergreen forest on clay or shale, often in damp places along stream banks; 500–900 m altitude.

Conservation status ― Vulnerable (VU). The conservation status was assessed by Wilmot-Dear et al. (2010: 443). It has been collected so seldom that it is believed to be uncommon and vulnerable to extinction if habitat conversion continues.

Notes ― 1. Yahara (1981: 15) recognised and mentioned the distinctive appearance of this taxon but did not describe it as new, apparently believing that the name B. erythropoda applied to this taxon. He had probably not seen the type of B. erythropoda (from Jawa) which is a different entity referable to the Southeast Asian taxon B virgata subsp. virgata var. virgata . Thin-leaved forms of B. virgata var. virgata are often similar in leaf shape and teeth, but differ in stems hairy, fruiting perianth with a wide wing and plants drying green rather than brown, flower-clusters often crowded along axis, male flowers in unisexual clusters on separate axes or separate branches.

2. This species appears to be rare and with a strangely disjunct distribution, but it is possibly overlooked, and might be expected to occur also in Indochina. Material seen is as follows: China, Yunnan, Xishuangbanna Dist., Jing Hong city, 21 v 1958, Class of 1958 no. 2437 (PE) ; Thailand (Pen.), Ranong, Khao Pawta Luang Keow , 30 i 1929, Kerr 16899 (K) & 22 vi 1974, Geesink et al. 7428 (AAU, BKF, K, L, S) ; Indonesia, Sumatera Utara [North Sumatra], Karo, Laubaleng , 4 ix 1974, S. Yoshida 1975 (L) .

3. It is very distinctive in its leaves extremely thin-textured, relatively large, shiny, elliptic, with hairs abundant and minute, marginal teeth indistinct, its veins, petioles and inflorescence-bearing axes distinctly red-tinged, and its slender inflorescence-bearing axes with clusters few-flowered and bisexual. However, some duplicates of these four collections were previously identified as either B. zollingeriana or B. hamiltoniana .

Boehmeria zollingeriana (sympatric but common and widespread) is rather similar in habit, fruit-form, leaf shape and -texture and in its red-tinged petioles, stems and inflorescence-bearing axes. Fertile specimens of B. zollingeriana are easily distinguished by their male clusters sessile, axillary with long-pedicellate 5 –6-merous male flowers and their inflorescence-bearing axes entirely female, robust with large flower-clusters; leaves of B. zollingeriana are also ovate, ± glabrous adaxially or with hairs longer (0.3–0.4 mm) but extremely sparse, basal veins extending little into distal half and some lateral veins arising nearer leaf base than in B. leptostachya .

Boehmeria hamiltoniana (sympatric but slightly more widespread) is somewhat similar to B. leptostachya in leaf shape and -texture and in the shape of its fruiting perianth, differing in leaves entirely glabrous adaxially, relatively narrower with acumen markedly long and marginal teeth mostly closer-spaced, female flower-clusters usually crowded along the axes and often many-flowered; in the dry state the two are easily distinguished, the leaves of B. hamiltoniana drying consistently distinctly greenish.

Figures

Map 12 Distribution of Boehmeria leptostachya Friis & Wilmot-Dear.

Fig. 9 Boehmeria leptostachya Friis & Wilmot-Dear. a. Part of stem with opposite leaf-pairs and bisexual inflorescence-bearing axes; b. detail of leaf margin; c. leaf, detail of adaxial surface; d. detail of abaxial surface; e. stipule; f. detail of inflorescence-bearing axis showing two bisexual flower-clusters (inflores- cences) in flowering stage; g. detail of inflorescence-bearing axis showing one bisexual flower-cluster (inflorescence) in fruiting stage (with pedicels of fallen male flowers); h. male bud; i, j. fruiting perianths (from different plants) (a–d, g: Geesink 7428, K; e, f, h, i: Kerr 16899, K; j: ‘Class of 1958’ 2437, PE). — Scale bars: a = 5 cm; b = 5 mm; c-j = 1 mm.