Digitaria petelotii Henrard (1934: 109)

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

15. Digitaria petelotii Henrard (1934: 109) . Type:— CAMBODIA, Kampong Cham, A. Pételot 263 (holotype P!; isotype L!).

Perennial. Culms decumbent or ascending, 35–80 cm high, internodes tomentose. Sheaths pilose, 3–5 cm long. Blades linear, 5–11 cm by 3–5 mm, both surfaces pilose, apex acuminate. Ligules ca. 0.5 mm long. Inflorescences composed of racemes; peduncles glabrous; common axis absent. Racemes 2–5, longest 8–10 cm long, digitate; rachis ribbon-like, winged, 0.7–0.8 mm wide, margin spicular, spicules ca. 0.1 mm long. Pedicels terete, spicular; abscission cupuliform. Spikelets ternate, sometimes a pedicel fused to the rachis, homomorphous, elliptic, 2.2–2.5 mm long, greenish to whitish, hairs verrucose with acute apex. Lower glume membranous, ca. 0.1 mm long, emarginate. Upper glume lanceolate, as long as the spikelet, chartaceous, apex acute, pubescent between nerves, nerves 5. Lower lemma as long as the spikelet, chartaceous, apex acute to acuminate, pubescent between nerves and on margin, nerves 7, inequidistant. Upper lemma as long as the spikelet, chartaceous to coriaceous, apex acute, yellowish. Anthers 0.6–0.8 mm long, yellowish. Caryopsis ellipsoid, 1.2–1.4 mm long, creamy. ( Figures 4I & 4J )

Distribution: — Thailand, Cambodia.

Selected specimens examined: — CAMBODIA. Kampong Cham: July 1921, A. Pételot 263 (P, L). THAILAND. Loei: Phu Kradueng, 25 August 1988, H. Koyama T-61311 (BKF). Ubon Ratchathani: Phu Chong Na Yoi National Park, 9 July 2009, B. Boonsuk 98 (BK, BKF, KKU, QBG). Sa Kaeo: Aranyaprathet, 8 October 1930, A.F.G. Kerr 19623 (BK, K). VIETNAM. Bình Dýõng: 16 August 1954, M. Schmid s.n. (P).

Ecology: —Open areas; elevation ca. 250 m.

Selected specimens examined: — Digitaria petelotii is a rare species found in a few localities in Cambodia, Thailand and Vietnam. We assess the status of this species as Vulnerable, or VU, according to IUCN (2012) criteria.

Note: — Digitaria petelotii is distinguished by its tomentose internodes and it is also densely pilose on its sheaths and both leaf surfaces. Its spikelets have emarginate lower glumes and pubescence with whitish verrucose hairs which are also overtopping to the spikelets.

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.