Themeda idjenensis Jansen

Veldkamp, J. F., 2016, A revision of Themeda (Gramineae) in Malesia with a new species from Laos, Blumea 61 (1), pp. 29-40 : 34

4. Themeda idjenensis Jansen

Themeda idjenensis Jansen (1952) 482. — Type: Koorders 42922 (holo L sh. 927.345-190; BO1460437 ).

Themeda arundinacea ( Roxb.) A.Camus var. densa Ohwi , nom. ined. — Vouchers: Backer 25150, 36946, bb 12218 (Satridihardjo), Bijhouwer 16, Clason­Laarman F116, Koorders 42922 (BO).

Themeda gigantea auct. non Hack.

Themeda gigantea (Cav.) Hack. subsp. avenacea auct. non Hack.

Plants perennial. Culms c. 3 m long, tufted. Nodes glabrous. Ligule 2–3 mm long, margin glabrous. Leaves at least 50 cm by 4–10 mm wide. Uppermost spatheoles glabrous. Peduncle 2–10 mm long, extremely short to c. 1/3 times as long as the spatheole, glabrous or white hairy. Capitules long-persistent. Involucral spikelets conspicuous, pairs unequally inserted, male; lower glumes linear-lanceolate to linear, 12–16 by 1.2–3 mm, acuminate to aristate, herbaceous, 11-nerved, glabrous; upper glumes 3-nerved. Fertile spikelets 1, 10–11 mm long (incl. callus), callus 1–3 mm long, hairs white, turning brown, 1.5–5 mm long; lower glumes castaneous, apex acute to truncate, surface dorsally, marginally, and distally puberulous to hairy all over, hairs white. Awn well-developed, 32–58 mm long, column 16–33 mm long (i.s.), straight, puberulous or minutely puberulous (40 ×!) or scaberulous, hairs white (i.s.). Anthers 3.7–7 mm long, purple i.s. Pedicel glabrous to hairy. Pedicelled spikelets 2, male, 10–16 mm long; lower glumes apex mucronate to aristate, glabrous.

Distribution — E Java (Ijen, G. Semongkrong, Tengger), Lesser Sunda Isl. ( Bali: Gilimanuk, Klungkung, P. Menjangan).

Habitat — Grass- and shrub jungle, noted by Van der Paardt (#2, BO) as aggressive and outcompeting other vegetation, on slopes, 10–1500 m altitude.

Collector’s notes — Forming gigantic tufts, close together. Flowering culms 3.1 m tall, brown green ( Rappard # C; L).

Notes — In view of the similarities with e.g. T. arundinacea and T. gigantea the plants are presumably tufted, tall, and have long leaves. The inflorescences are probably also large but collections consist of only parts of them.

The lower glumes of the fertile spikelet appears variable in the colour of the pubescence. Apparently the hairs are snow white when young, and gradually turn brown, but may bleach to white again.

The pedicelled spikelets are sometimes so similar to the involucral ones and inserted so close to them with very brief pedicels, that at first sight they appear to be absent, and that the 6 (!) involucral spikelets are inserted unequally.

The occurrence in Klungkung ( bb 12218 ( Satridihardjo), BO) is surprising, as it is not so dry there as in the other localities.