Digitaria thwaitesii (Hack.) Henrard (1934: 101)

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 : 270-271

24. Digitaria thwaitesii (Hack.) Henrard (1934: 101) .— Panicum thwaitesii Hack. (1901c: 334) . Type:— SRI LANKA, G.H.K. Thwaites 857 (US-1126069 (fragm.)).

24.1 Digitaria thwaitesii (Hack.) Henrard var. tonkinensis Henrard (1950: 742) . Type :— VIETNAM, Tonkin, B. Balansa 1659 (holotype P!; isotype K!, not found in L).

Perennial. Culms tufted, rhizomatous, robust, strictly erect, 25–130 cm high; nodes glabrous; internodes glabrous. Sheaths 4.5–8 cm long, glabrous. Ligules ca. 1 mm long. Blades linear, 7.5–30 cm by 3–7 mm, apex acuminate, margin scabrous, both surfaces glabrous. Inflorescences composed of racemes; peduncles pilose; common axis 2–4.5 cm long. Racemes 3–7, longest 9.5–13 cm long, digitate or subdigitate; rachis slightly triquetrous, winged, usually straight, 0.6– 0.8 mm wide, serrate. Pedicels terete, with short spicules; abscission discoid, the longest pedicels 1.5–2 times as long as the length of spikelet. Spikelets ternate, homomorphous, 2–2.6 mm long, elliptic, apex acute; hairs verrucose with acute apex, overtopping at summit. Lower glume collar-shaped, 0.1–0.2 mm long, membranous, glabrous. Upper glume elliptic, as long as spikelets, chartaceous, pubescent between the nerves, nerves 5, equidistant. Lower lemma elliptic, as long as spikelets, apex acute, chartaceous, pubescent between the nerves with or without glabrescent interspaces beside the midnerve, nerves 7, inequidistant; palea triangular, ca. 0.2 mm long, chartaceous. Upper lemma 1.9–2.5 mm long, coriaceous, apex acute, brown to dark brown. Anthers 0.6–0.7 mm long, yellowish. Caryopsis ellipsoid, 1.2–1.7 by 0.5–0.7 mm, whitish to yellowish.

Distribution: — Thailand, Vietnam.

Selected specimens examined: — THAILAND. Phetchabun: Lom Kao , 4 May 1955, T. Smitinand 2611 ( BKF) ; Khao Kho, Thung Salaeng Luang National Park , 5 Dec 2009, B. Boonsuk 182 ( BK, BKF, K, KKU) ; ibid., 20 Jun 2010, B. Boonsuk 288 ( BK, BKF, KKU, QBG). Loei: Phu Ruea National Park, 18 December 2005, C. Jaroenchai 279 ( KKU). Ubon Ratchathani: Khong Chiam , Pha Taem National Park , 10 July 2009, B. Boonsuk 105 ( KKU) . VIETNAM. Hanoi: Sontay, 27 September 1938, A. Pételot 2040 ( BO, P). Quang Ninh: Quang Yen , 15 April 1886, B. Balansa 1659 ( K, P) .

Ecology: —Deciduous forests; elevation 300–500 m.

Conservation status: — Digitaria thwaitesii var. tonkinensis is found in small areas of the northeast of Thailand and the north of Vietnam. Its conservation status is classified as DD according to IUCN (2012) criteria.

Notes: — Henrard (1950) cited L as the place of deposit of the holotype of var. tonkinensis . This is in accordance with Balansa’s Indochinese grasses being deposited there, but this specimen could not be found (Veldkamp 1973). It is therefore better to regard the duplicate in P as the holotype. Veldkamp (1973), Lazarides (1980) and Chen & Phillips (2006) regarded it is a synonym of D. violascens but Boonsuk et al. (2014b) agreed with Henrard (1950) and reinstated it to remain a variety of D. thwaitesii .

Digitaria thwaitesii is recognised by its small, tufted and erect habit. It is rhizomatous and has glabrous leaves and brown upper florets. Digitaria thwaitesii var. tonkinensis is distinguished by its pilose peduncles, spikelets with overtopping hairs, and collar-shaped lower glume. The lower lemma is usually pubescent in all the spaces between the nerves. However, it sometimes has glabrous interspaces beside the midnerve.