Mnesithea helferi (Hook.f.) de Koning & Sosef

Veldkamp, J. F., Heidweiller, J., Klaauw, M. A. F. van der, Koning, R. de, Kraaijeveld, A. R., Sosef, M. S. M. & Strucker, R. C. W., 2013, A revision of Mnesithea (Gramineae - Rottboelliinae) in Malesia and Thailand, Blumea 58 (3), pp. 277-292 : 283

6. Mnesithea helferi (Hook.f.) de Koning & Sosef — Fig. 6

Mnesithea helferi (Hook.f.) de Koning & Sosef in Veldkamp et al.(1986) 291. — Rottboellia helferi Hook.f. (1896) 158. — Coelorachis helferi (Hook.f.) Henrard (1941) 518. — [ Rottboellia corymbosa L.f. subvar. helferi (Hook.f.) Roberty (1960) 65, comb. inval.]. — Type: Helfer 913 (holo K).

Mnesithea rupincola Ridl.(1911a) 116. — [ Rottboellia corymbosa L.f. subvar. rupincola (Ridl.) Roberty (1960) 65, comb. inval.]. — Type: Ridley 14351 (holo SING; BM, K). Roberty erroneously cited Ridley 372 as the type.

Plants perennial. Culms 0.4–0.8 m long, glabrous. Cataphylls ovate-oblong, (2.5–)11–26(–35) by (1.5–)2.5–3.8(–5.2) mm, puberulous to ciliate along the margins, apex acute. Nodes puberulous to setose. Sheaths sparsely hairy to hairy, margin pilose to ciliate. Ligule 0.7–2.7 mm long, margin setose. Contra-ligule absent. Blades flat to folded, (14–)22–36(–48) cm by 5 –13 mm, margins pectinate at base, glabrous to hairy on both sides or glabrescent, glabrous to setose behind the ligule, smooth. Peduncles solitary or paired, glabrous. Spatheoles 5.5–14 cm long. Spikes (3–)5.5–7.5(–10) cm by 1.5–3 mm. Spikelets paired, rarely in triads (see note). Joints 3.2–4 mm long, ciliolate to hairy at base. Sessile spikelets 4.8–5.5 mm long (incl. callus), longer than the joint. Callus ciliolate. Lower glume flat to convex, ovate-oblong, glabrous or minutely puberulous, chartaceous to coriaceous, smooth, greenish yellow, 5 –7-nerved, lower part with or without small appendages, apex winged; upper glume boat-shaped, ovate-oblong, 3.7–5 mm long, 3–4-nerved, nerves not anastomosing, ciliolate along the infolded margin, apex acute. Lemmas ovate-oblong, 2.8–3.6 mm long, ciliolate along the margin, apex acute; first lemma paleate, 3.2–3.6 mm long, 3-nerved; second lemma 3-nerved. Paleas 2-nerved, glabrous; first palea ovate-oblong, 2.2–2.7 mm long; second palea ovate-lanceolate, 1.6–2.2 mm long. Anthers 1.3–1.5 mm long. Pedicel free from the joint, 3–4.8 mm long, pubescent. Pedicelled spikelets from virtually absent to 1 mm long and reduced to 2 glumes, laterally flattened. Lower glume chartaceous, margins ciliolate, apex winged.

Distribution — Burma (Tenasserim), Thailand (NE: Nong Khai; SE: Chanthaburi; C: Saraburi), Cambodia (Kratie), S Vietnam (Biên Hoa), Malesia: Malay Peninsula (Kedah, Penang, Perak).

Habitat — Rocks in river, shaded more or less dense evergreen forest, c. 150 m altitude.

Notes — The differences with M. glandulosa are but slight (see key). Future research will have to show whether two taxa can be maintained.

Nguyen Van Khiem 148 (L), Vietnam (Biên Hoa), may represent the form mentioned by Schmid (1958: 191) as Rottboellia 5. It has joints with two sessile and one pedicelled spikelets as are also present in the type Helfer 913. Poilane 19 Jul 1932 (L, P) also from Biên Hoa, was ‘normal’.

Differs from the Malesian / Thai congeners in: Culms 0.4–0.8 m long. Sessile spikelet 4.8–5.5 mm long (incl. ciliolate callus).

Most similar is M. glandulosa (see key).

Figures

Fig. 6 Mnesithea helferi (Hook.f.) de Koning & Sosef. a. Sessile spikelet; b. sessile spikelet and joint (all: Maxwell 74-586, L).