Digitaria fuscescens (J. Presl) Henrard (1930: 8)

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 : 257-258

7. Digitaria fuscescens (J. Presl) Henrard (1930: 8) .— Paspalum fuscescens J. Presl (1830: 213) .Type:— PHILIPPINES, T. Haenke s.n. (holotype PR; isotypes L!, MO, US-2630404 (fragm.), W).

Digitaria pseudo-ischaemum Buse (1854: 42 ; 382). Type:— INDONESIA, Sumatra, F.W. Junghuhn s.n. (holotype L!).

Annual or perennial. Culms creeping and decumbent, 30–50 cm high, nodes pilose or glabrescent. Sheaths 1.2–2.5 cm long, glabrescent. Ligules 1–2 mm long. Blades linear-lanceolate, 1.5–2(–5) cm by 3–5 mm, apex acute, margin serrulate and sinuate at one side, both surfaces smooth or sparsely setose with bulbous base hairs. Inflorescences composed of racemes; peduncles glabrous; common axis absent. Racemes 2–6, longest 3–6.5 cm long, digitate; rachis ribbon-like, winged, 0.9–1.1 mm wide, entire to serrulate. Pedicels terete, glabrous; abscission cupuliform to discoid. Spikelets ternate, homomorphous, elliptic, 1.4–1.7 mm long, glabrous. Lower glume absent or rarely up to 0.3 mm long, membranous. Upper glume elliptic, 1.4–1.7 mm long, chartaceous, apex acute, glabrous, nerves 3–5. Lower lemma 1.4–1.7 mm long, chartaceous, apex acute with purple, nerves 7, equidistant. Upper lemma 1.4–1.6 mm long, chartaceous, apex acute, yellowish. Anthers 0.5–0.6 mm long, purple. Caryopsis oblong-ellipsoid, 0.9–1 mm long, creamy. ( Figures 3C & 3D )

Distribution: — Mauritius, Bourbon, Madagascar, India, Sri Lanka, Myanmar, Thailand, S. China, Malaysia, Pacific, introduced elsewhere.

Selected specimens examined: — MYANMAR. Tanintharyi: Dawei, 15 August 1961, J. Keenan, U T. Aung & R.H. Rule 732 (K). PENINSULAR MALAYSIA. Kelantan: 7 July 1935, M.R. Henderson SF 29588 (P, SING). Selangor: Kepong, 22 December 1929, C.F. Symington 21411 (KEP). Johore: 20 June 1965, J. Sinclair 10816 (K), 10817 (SING). THAILAND. Kanchanaburi: Si Sawat, 20 Feb 1967, C. Chermsirivathana 643 (BK). Surat Thani: Ko Samui, Ban Bua Phut, 14 May 1928, A.F.G. Kerr 15715 (BK, BM, K). Phatthalung: Pa Phayom Reservoir, Pa Phayom, 31 March 2012, B. Boonsuk 627 (BK, BKF, KKU, QBG). Songkhla: Hat Yai, Khlong Hoi Khong, 19 May 1986, J.F. Maxwell 86-307 (BKF, L, PSU). Narathiwat: Cho Ai Rong, 9 July 1923, A.F.G. Kerr 7140 (BK, K). VIETNAM. Hanoi: Sontay, 20 December 1920, P. Couderc s.n. (P).

Ecology: —On moist sandy to rocky soil, open places, beaches, dunes or fields.

Conservation status: — Digitaria fuscescens is common in tropical Asia and abundant in the peninsular region. We classify this species as LC according to the IUCN (2012) criteria.

Note: —This species is often misidentified as D. longiflora because of the similarity in their habit and inflorescence. Digitaria fuscescens is, however, readily distinguished by its spikelets that are absolutely glabrous with purplish tips whereas the spikelets of D. longiflora have whitish verrucose hairs.

Figures

FIGURE 3. SEM micrographs of spikelets of some Digitaria species from mainland SE Asia. A–B. D. abludens (from S. Laegaard & M. Norsangsri 21666): A. lower lemma; B. upper glume. C–D. D. fuscescens (from B. Boonsuk 627): C. lower lemma; D. upper glume. E–H. D. bicornis (from B. Boonsuk 341): E–F. subsessile spikelets; E. lower glume and lower lemma; F. upper glume. G–H. pedicelled spikelets; G. lower glume and lower lemma, sericeous hairs and bristles on lower lemma; H. upper glume. I–J. D. ciliaris (from B. Boonsuk 375): I. lower glume and lower lemma; J. upper glume. K–L. D. nuda (from B. Boonsuk 286): K. lower glume; L. upper glume. Scale bar: A–D = 200 μm, E–L = 400 μm.