Digitaria thyrsoidea Balansa (1890: 138)

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 : 271-272

25. Digitaria thyrsoidea Balansa (1890: 138) . Type :— VIETNAM, Cam Ranh Bay, B. Balansa s.n. (holotype L!; isotype P!).

Digitaria quinhonensis A. Camus (1921: 456) . Type:— VIETNAM, Annam, Quinhon, B. Balansa s.n. (holotype L!; isotype P!). Paspalum subcorymbosum A. Camus (1912: 223) .— D. subcorymbosa (A. Camus) A. Camus (1922: 406) . Type:— CAMBODIA, Pursat,

A. Godefroy 382 (lectotype P!, photo in K!), designated by Henrard (1950).

Perennial. Culms tufted, 80–120 cm high, erect. Sheaths (6–)8–12(–14) cm long, glabrous. Ligules 2–4.5 mm long. Blades linear, 12–30 cm by 7–15 mm, base attenuate, apex acuminate, margin serrulate; both surfaces scabrous, setose or sparsely pilose. Inflorescences composed of racemes; peduncles glabrous; common axis 4.5–9 cm long, robust. Racemes 5–18, longest 10–13(–16) cm long, verticillate or subdigitate, patent, raceme at apex usually erect; rachis triquetrous, 0.4–0.5 mm wide, margin serrulate, sometimes setose along the raceme. Pedicels serrulate; abscission cupuliform. Spikelets binate, homomorphous, lanceolate, 2.8–3 mm long, lax, apex acute, hairs smooth with acute apex. Lower glume elliptic, 0.2–0.3 mm long, chartaceous, apex obtuse. Upper glume ovate to elliptic, 0.3–0.4 mm long, membranous, apex truncate to emarginate, pubescent between midnerve and on margins, nerve 1. Lower lemma lanceolate, 2.8–3 mm long, chartaceous, apex acute, pubescent between nerves and on margins without glabrous interspaces, nerves 7, equidistant. Upper lemma 2.6–2.8 mm long, chartaceous, apex acute, dark brown. Anthers 1.1–1.3 mm long, yellowish. Caryopsis ellipsoid, ca. 1 mm long, creamy.

Distribution: — Thailand, Lao PDR, Cambodia, Vietnam.

Selected specimens examined: — THAILAND. Phetchabun: Nam Nao National Park, 15 May 2012, B. Boonsuk 631 (KKU). Sakon Nakhon: Phu Phan National Park, 26 September 2010, B. Boonsuk 427 (BKF, KKU). Ubon Ratchathani: Phu Chong Na Yoi National Park, 9 July 2009, B. Boonsuk 99 (BKF, KKU). LAO PDR. Bolikhamsai: Phu Khao Khwai, 26 June 2010, B. Boonsuk & S. Lanosavanh 296 (KKU, Biology Herbarium NUOL). CAMBODIA. Pursat: A. Godefroy 382 (P). VIETNAM. Gai Lai: Ayun Pa, J. Dournes s.n. (P).

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

Conservation status: — Digitaria thyrsoidea is an Indo-Chinese species occurring in Thailand, Lao PDR, Cambodia and Vietnam. We assess the conservation status of this species as LC according to IUCN (2012) criteria.

Note: —Although the characteristics of upper glume of D. quinhonensis , D. subcorymbosa and D. thyrsoidea were previously applied to separate each species ( Camus 1921 & 1922, Henrard 1950), we found that the upper glume is very variable in length but shorter than half the length of the spikelets and similar to occuring in D. setigera . We conclude that they are the same species and treat them as D. thyrsoidea corresponding to Boonsuk et al. (2014a). Distinguishing characters of D. thyrsoidea include its greyish-green leaves (on the lower leaf surface) and a large inflorescence with a robust common axis bearing an erect raceme at its apex. Its lower lemmas have equidistant nerves and its upper florets are dark brown.

The type specimen of Paspalum subcorymbosum or D. subcorymbosa (A. Godefroy 382) from P was selected as the lectotype by Henrard (1950) not a holotype as mentioned in Boonsuk et al. (2014a).