Boehmeria yaeyamensis Hatus.

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 : 196-197

30. Boehmeria yaeyamensis Hatus. — Fig. 36g –m ; Map 38

Boehmeria yaeyamensis Hatus. (1979) 34. ― Syntypes: Hatusima 24563 (KAG), 24564 (KAG), Japan, Ryukyu Islands, Yonakuni Island.

Robust erect woody-based herb or subshrub, 0.3–0.8 m tall; ultimate branchlets robust, 1.5–3 mm diam; hairs of two kinds, dense, short (≤ 0.1 mm), spreading hairs mixed with sparser coarser longer (0.2–0.3 mm) ones, some bulbous-based, soon glabrescent. Stipules 3–5 by 1.5–2.5 mm, thick-textured. Leaves opposite, moderately dimorphic in size only, ‘larger’ leaf with length of lamina only 1.2–1.5 ×, but length of petiole 2 –3 × that of ‘smaller’ ones; very broadly ovate, rhombic-ovate or deltate, 4–10 by 3–9 cm, length 1.1–1.3 × width; margin crenate, teeth few, 7–10 either side, often of irregular width but always broad and shallow, 1.5–4 by 4–7 mm, width 2–3 × length; leaf apex obtuse or broadly acute and rounded or mucronate at extreme tip; base broadly rounded, truncate or slightly cordate, rarely broad-cuneate; basal veins extending into distal half, upper lateral veins similarly arranged on both sides of leaf, 1– 2 arising in distal half, main veins and reticulation thinly prominent abaxially; texture thick-(rarely thin-)chartaceous to coriaceous; adaxial surface drying dark green, rough with bulbous-based hairs like the longer ones on the stem, sparse to abundant; abaxial surface drying much paler, with hairs abundant but soft, shorter, finer, often half-adpressed, often so dense that abaxial surface appears velvety; petiole relatively long often 0.25–0.75 × lamina length. Inflorescence-bearing axes only 1–6 cm long, unbranched, 1 per axil, all axes seen with mostly female flowers, male flowers 1–few in occasional clusters on some axes and mostly near the apex, clusters so densely crowded as to give whole axis a cylindrical appearance 5 – 6 cm diam with individual clusters more or less indistinguishable; each cluster with usually more than 50 densely congested female flowers; bracteoles 0.5–1 mm long but inconspicuous in densely congested clusters. Male flowers 4-merous, sessile, mature buds c. 1 mm diam, globose, tepals without dorsal appendage, hairs abundant, mostly bulbous-based like on stem. Female flowers ellipsoid to obovoid, c. 0.8 by 0.25 mm, with finer hairs than on male flowers; stigma c. 1 mm long. Fruiting perianth slightly asymmetrically ellipsoid to obovoid or oblong with ± truncate apex, often 3-angled, 1.5–2 by 0.6–1 mm, without beak, slightly laterally flattened in lower part containing achene and with inflated wing-like distal part, densely hairy near apex. Achene subspherical, 0.5 mm diam.

Distribution ― Endemic to Japan (south-western Ryukyu Islands, Yaeyama Island: Yonakuni, Ishigaki).

Habitat & Ecology ― Roadsides and dry sunny open coral limestone cliffs near seashore; at or near sea level.

Conservation status ― We are uncertain whether to assess it as Near Threatened (NT) or Endangered (EN). It is known from only seven collections from two localities but the level of risk to its particular habitat, some of which is protected on these islands, is uncertain. Tentatively it is given the status of Endangered (EN) on the criteria EN B2ab(iii).

Notes ― 1. A species endemic to the Ryukyu Islands, distinctive in leaves small, broad, often thick-textured, few-toothed large-crenate, short thick unbranched inflorescence-bearing axes with densely congested mainly female clusters, few scattered male flowers and apparently no separate male axes, male tepals without dorsal appendage and two kinds of hairs on the stem.

Similar in habit, indumentum, leaf texture and crowded female clusters to B. splitgerbera , which is often of similar habitat but allopatric (eastern and north-eastern Japan) and differing in ± isomorphic somewhat misshapen leaves often bilobed at apex and numerous (30–40) much smaller teeth.

2. It also bears some resemblance to certain individuals of a range of coastal entities found in eastern and north-eastern Japan and South Korea. These are allied to B. splitgerbera but have mostly been identified as ‘ B. gigantea ’ (= B. holosericea ). They are similar to B. yaeyamensis in having two kinds of hairs on the stem and thick-textured leaves, but differ in much larger isomorphic leaves with more numerous teeth (usually over 20 each side) and acuminate apex. A group of such entities was studied by Yahara (1983a: 234–243) in Honshu who suggested them to be hybrids of B. splitgerbera with the other parent uncertain (see further discussion and list of types falling within this variation under B. splitgerbera in Note 4, 5).

Figures

Map 38 Distribution of Boehmeria splitgerbera Koidz. (●) and B. yaeya­ mensis Hatus. (Ê).

Fig. 36 a–f: Boehmeria splitgerbera Koidz. a. Habit of stem with inflorescence-bearing axes, in lowermost part of plant pendulous male axes, above erect, congested female axes; b–d. leaves from different plants; e. male bud; f. fruiting perianth. — g–m: Boehmeria yaeyamensis Hatus. g. Upper part of stem showing congested erect inflorescence-bearing axes; h. detail of stem showing stipules and base of paired axillary inflorescence-bearing axes concealing petiole base; i. leaf, detail of abaxial surface; j. portion of inflorescence-bearing axis showing congested female flower-clusters (inflorescences) and bracts; k. male bud; l, m. fruits of different form from same plant (a, f: Furuse 26669; b, e: Hort Kew s.n.; c: Furuse 28436; d: Koyama 268; g–j: Furuse 4213; k: Furuse 3199; l, m: Furuse 4148; all K). — Scale bars: a = 5 cm; b, g = 2 cm; c, d = 1 cm; e, f, k–m = 1 mm; h-j = 2 mm.