Digitaria pusilla Ridl. (1925: 215)

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 : 263-264

16. Digitaria pusilla Ridl. (1925: 215) . Type:— THAILAND, Satun (Setul), H.N. Ridley 14866 (lectotype K!; isolectotypes BM!, SING!), designated by Henrard (1950).

Annual. Culms tufted and ascending, 10–25 cm high. Sheaths 0.7–1 cm long, densely pilose. Blades linear, 1.6–3.5(–5) cm by 1–2 mm, apex acute to acuminate, both surfaces densely pilose. Ligules up to 0.2 mm long. Inflorescences composed of racemes; peduncles glabrous; common axis absent. Racemes 2, rarely 3, longest 1.5–3 cm long, digitate; rachis slightly triquetrous, winged, wavy, ca. 0.3 wide mm, serrulate. Pedicels terete to trigonous; abscission cupuliform to discoid. Spikelets ternate at least in the lower part and binate in the upper part of racemes, homomorphous, elliptic, 1–1.2 mm long, apex acute, pubescent, hairs verrucose with acute apex. Lower glume collar shaped, ca. 0.1 mm long, membranous. Upper glume ovate, ca. 1 mm long, chartaceous, apex acute, purplish, nerves 5. Lower lemma lanceolate, ca. 1 mm long, chartaceous, apex acute, pubescent between nerves, nerves 7, equidistant. Upper lemma lanceolate, as long as the spikelet or slightly protruding above the lower lemma, coriaceous, apex acute, brown. Anthers 0.2–0.3 mm long, purple. Caryopsis ellipsoid, 0.6–0.7 mm long, brownish. ( Figures 4K & 4L )

Distribution: —Rare, Thailand, Malaysia.

Selected specimens examined: — PENINSULAR MALAYSIA. Kedah: Langkawi, 12 November 1941, J. C. Nauen SF 38110 ( BO, K, SING). THAILAND. Surat Thani: Ko Tao , 20 September 1918, A. F. G. Kerr s.n. ( BM) ; ibid., 31 December 1926, A. F. G. Kerr 11198 ( BK, K). Satun: March 1910, H. N. Ridley 14866 ( K, BM, SING) .

Ecology: —Sandy soils; elevation up to 300 m.

Conservation status: — Digitaria pusilla is very rare and known from a few collections from Thailand and Malaysia. This species is assessed as EN according to IUCN (2012) criteria.

Note: —This rare species is one of the small-sized species in habit, inflorescences and spikelets. The leaf sheaths and blades of D. pusilla are densely hairy.

Figures

FIGURE 4. SEM micrographs of spikelets of some Digitaria species from mainland SE Asia. A–D. D. heterantha (from M. Norsaengsri 2827): A–B. subsessile spikelets; A. lower glume and lower lemma, lower lemma with closed nerves and slit-like interspaces between nerves; B. upper glume. C–D. pedicelled spikelets; C. lower glume and lower lemma, lower lemma pubescent with sericeous hairs and bristles; D. upper glume. E–F. D. longiflora (from B. Boonsuk 370): E. lower glume and lower lemma; F. upper glume. G–H. D. mollicoma (from B. Boonsuk 164): G. lower glume and lower lemma; H. upper glume. I–J. D. petelotii (from B. Boonsuk 98): I. lower glume and lower lemma; J. upper glume. K–L. D. pusilla (from A.F.G. Kerr 11198): K. lower glume and lower lemma; L. upper glume. Scale bar: A–D. & G–J. = 400 μm, E–F. & K–L. = 200 μm.