Boehmeria siamensis Craib

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 : 131-133

16. Boehmeria siamensis Craib — Fig. 14 ; Map 15

Boehmeria siamensis Craib (1916) 269. ― Syntypes: Kerr 538 (K; isosyn TCD), northern Thailand, Chiang Mai, Doi Sutep; Hosseus 455 (K), Thailand, Chiang Mai [Chengmai].

Boehmeria spirei Gagnep. (1950) 35. ― Type: Spire 1546 (holo P), Laos, Xieng-Kung.

Boehmeria chiangmaiensis Yahara (1981) 18, syn. nov. ― Type: Nimanong et al. 1726 (holo BKF), northern Thailand, Chiang Mai, Hod. – See Note 2.

Large or small shrub, up to 3.5 m, often sparsely-branched, rarely small tree; ultimate branches robust, 2–2.5 mm diam, hairy, hairs sparse or abundant, fine, short, adpressed soon glabrescent. Stipules narrowly triangular, c. 6 by 2 mm, thick-textured. Leaves opposite (sometimes some subopposite on lateral stems), scarcely dimorphic with ‘larger’ leaves up to 1.2 × length of ‘smaller’ ones, narrowly elliptic or ovate, usually medium or large, (4–)12–24(–28) by (1.5–)4.5–12(–15) cm, length 2 –3 × width; margin shallowly serrate (rarely more deeply crenate-serrate, teeth 25–40 either side, 1(–3) by 1.5–5(–7) mm; leaf apex broadly acute sometimes with abrupt tiny acumen at extreme tip; base broadly or narrowly cuneate to more or less rounded, sometimes slightly asymmetrical; basal veins hardly curved, extending into distal third or quarter of lamina; upper lateral veins similarly arranged on both sides of midrib, 3(–4), often hardly distinct from coarser tertiary venation, all arising in distal third of lamina, inconspicuous adaxially, prominent abaxially; coarser tertiary venation conspicuously scalariform, close-spaced, 2–4 mm apart, finer tertiary venation reticulate, all venation visible adaxially, rather reddish, prominent abaxially; texture coriaceous (rarely thin-chartaceous in dense forest); adaxial surface pubescent, hairs abundant, fine, ± adpressed, giving rather rough feel; abaxial surface with hairs on veins only, these very sparse, otherwise glabrous, rather yellowish and slightly gleaming in dry state; petiole very short relative to lamina, c. 0.05 × length, 0.7–1 cm. Flower­clusters borne on leafless axes, these pendulous, unbranched, a pair (rarely only one) arising from each axil or sometimes apparently many in a congested mass but these in fact arising from axils of short axillary leafy shoots; male and female inflorescence-bearing axes often on same plant with male ones in upper axils; male axes relatively short, 3– 5 cm long, female axes up to 15 cm long, some axes bearing both male and female clusters; bracts exceeding mature clusters and therefore conspicuous (recorded as pink in bud), often visible even in fruiting clusters, broadly ovate-triangular, 2–2.5 by 1.5–2.5 mm, width often equalling length, apex often broadly rounded, blunt; clusters crowded, usually more or less contiguous, male clusters 3–4 mm diam, with c. 10 flowers, female clusters 4–5 mm diam, with over 30 densely crowded flowers. Male flowers 4-merous, sessile, mature buds globose sometimes slightly flattened, (1.2–) 1.5–2 mm diam, dorsal thickening inconspicuous, pubescence dense, short, spreading. Female flowers recorded as white tinged purple, 1–2 by 0.3–0.6 mm, spindle-shaped tapering into indistinct pedicel, hairy like male; stigma 0.6–1 mm. Fruiting perianth yellow-brown, spindle-shaped or elliptic in outline, markedly laterally flattened into distinct marginal wing up to quarter of total fruiting perianth width either side, also with very short broad beak and two distinct apical teeth. Achene spindle-shaped, large, c. 2.3 by 0.8–1 mm, filling fruiting perianth.

Distribution ― Nepal, Burma, southern China, northern and western Thailand, Laos.

Habitat & Ecology ― Evergreen forest, and disturbed areas in forest remnants, secondary grassland on granite, open hillsides; (300–) 500–2750 m altitude.

Conservation status ― Near Threatened (NT). The species is known from c. 30 collections, some of which are recent, and it occurs in fairly scattered locations, with some considerable gaps in the range. The EOO of 1 401 620 km 2 is therefore probably exaggerated, and the AOO gives a figure of less than 500 km 2. It occurs in a moderate range of habitats, mainly forests. Although these 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 the region.

Notes ― 1. This species is not easily confused with any other taxa. It is distinctive in its leaves with tertiary veins scalariform, prominent, reddish, giving a reached appearance to leaves, and close-spaced, apex broad-acute, teeth numerous, abaxial surface drying markedly paler (yellow-brown or chestnut-brown) and almost glabrous, leaves usually also thick-textured (only some very low altitude collections thin-textured), in its inflorescence-bearing axes at least 2 from each axil, with subtending bracts conspicuous, broad, longer than the flower-clusters and in its fruiting perianth and achene spindle-shaped.

The species which it most closely resembles is B. kurzii which differs in leaves entire, membranous and flower-clusters well-spaced. The ridge-like close scalariform venation is also very like that of B. polystachya which differs in branching inflorescence-bearing axes with inconspicuous bracts.

2. Yahara (1981) discussed in detail the similarities and differences amongst Thai species of Boehmeria , but was apparently unaware of the publication of the name B. siamensis , to which the description of his new species B. chiangmaiensis clearly conforms.

Figures

Map 15 Distribution of Boehmeria siamensis Craib.

Fig. 14 Boehmeria siamensis Craib. a. Habit of stem with inflorescence-bearing axes; b. leaf, abaxial surface; c. detail of one node with young inflorescencebearing axes; d. detail of male inflorescence-bearing axis with congested flower-clusters (inflorescences) and bracts; e. male bud; f. detail of female axis with congested flower-clusters (inflorescences) and bracts; g. fruiting perianth (a, g: Harder et al. 4928; b: Kerr 538; c: Geesink 8042; d, e: Nooteboom 791; f: Hosseus 455; all K). — Scale bars: a, b = 2 cm; c = 5 mm; d, f = 2 mm; e, g = 1 mm.