Digitaria tomentosa (J. König ex Rottler) Henrard (1934: 100)

Boonsuk, Boonchuang, Chantaranothai, Pranom & Hodkinson Abstract, Trevor R., 2016, A taxonomic revision of the genus Digitaria (Panicoideae: Poaceae) in mainland Southeast Asia, Phytotaxa 246 (4), pp. 248-280 : 272

26. Digitaria tomentosa (J. König ex Rottler) Henrard (1934: 100) .— Milium tomentosum J. König ex Rottler in Rottler & Willd. (1803: 220). Type:— INDIA, Tamil Nadu, Vandavasi (“Mt. Wandiwash”), 4/ 5 Jan 1800, Rottler s.n. (No specimen in the Herb. Willdenow, expected in E, K or LIV).

Annual. Culms up to 70 cm high, rooting at lower nodes; nodes brownish, pubescent. Sheaths 3.5–5.5 cm long, setose near the margin and lower part. Ligules 2–2.5 mm long. Blades linear, 13–20 cm by 5–9 mm, membranous, apex acuminate, margin smooth or serrulate, both surfaces tomentose or glabrous. Inflorescences paniculate with 20–30 long filiform branches, the longest branch 6–9 cm long; peduncles glabrous; common axis 5–15 cm long. Branches filiform, triquetrous, ca. 0.3 mm wide, serrate. Spikelet solitary or binate, homomorphous, lanceolate, 1.9–2.1 mm long, apex acute; hairs smooth with acute apex; dispersed throughout the panicle. Pedicels filiform, trigonous, serrate; abscission cupuliform. Lower glume very small, ca. 0.05 mm long, membranous, apex obtuse. Upper glume oblong, 0.2–0.3 mm long, membranous, apex obtuse. Lower lemma narrowly elliptic, as long as the spikelet, chartaceous, apex acute to truncate, pubescent between nerves and on margins without glabrous interspaces, nerves 7; palea absent. Upper lemma 1.7–1.9 mm long, chartaceous, apex acute, yellowish to brownish. Anthers not seen. Caryopsis oblong-ellipsoid, 1.2–1.5 mm long, brownish. ( Figures 5I & 5J )

Distribution: — India, Sri Lanka, Thailand.

Selected specimens examined: — THAILAND. Kanchanaburi: Sai Yok, 12 September 2005, J.F. Maxwell 05- 484 (BKF, CMUB). Ratchaburi: 19 July 1924, A.F.G. Kerr 9045 (BK, BM, K). Phetchaburi: Cha-am, 23 October 2014, B. Boonsuk 713 (BK, BKF, KKU).

Conservation status: —This is a predominantly Indian species but it is found on limestone mountains in only three locations of the South-West of Thailand. The species is categorised as LC based on IUCN (2012) criteria.

Ecology: —Mixed deciduous forests, on tops of limestone mountains; elevation 200– 350 m.

Note: — Digitaria tomentosa is easily separated from other species of Digitaria in Thailand by its distinctively paniculate inflorescences with slender rachis and pedicels. Its leaves are usually tomentose but the glabrous leaves could be found in B. Boonsuk 713.

Figures

FIGURE 5. SEM micrographs of spikelets of some Digitaria species from mainland SE Asia. A–B. D. radicosa (from B. Boonsuk 216): A. lower glume and lower lemma; B. upper glume. C–D. D. setifolia (from B. Boonsuk 232): C. lower glume and lower lemma; D. upper glume. E–F. D. stricta var. glabrescens (from B. Boonsuk 478): E. lower lemma; F. upper glume and upper lemma. G–H. D. ternata (from B. Boonsuk 330): G. lower glume and lower lemma; H. upper glume. I–J. D. tomentosa (from J.F. Maxwell 05-484): I. lower lemma; J. upper glume and upper lemma. K–L. D. violascens (from B. Boonsuk 297): K. lower lemma; L. upper glume. Scale bar: A–D. & G–J. = 400 μm, E–F. & K–L. = 200 μm.