Digitaria setifolia Stapf (1898: 376)

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 : 265-266

18. Digitaria setifolia Stapf (1898: 376) . Type :— SOUTH AFRICA, Albany Division, P. MacOwan 1300 (lectotype K!; isolectotype W), designated by Henrard (1950).

Panicum fibrosum Hack. (1901c: 330) .— D. fibrosa (Hack.) Stapf (1912: 428) , Type:— CHINA, Guangdong, Guangzhou, G.T. Sampson s.n. (lectotype K!), designated by Henrard (1950).

Perennial. Culms tussocky, erect, 90–120 cm high. Sheaths 13–17 cm long, pubescent, breaking to fibres at base. Blades filiform to narrowly linear, (15–) 30–40 cm by 1–3 mm, chartaceous, apex acute, upper surface scabrous, lower surface glabrous. Ligules 0.5–0.6 mm long. Inflorescences composed of racemes; peduncles glabrous; common axis 1–7 cm long. Racemes 2–3, longest 13–15 cm long, subdigitate or alternate along the common axis; rachis filiform, triquetrous, not winged, 0.3–0.4 mm, serrate. Pedicels terete; abscission cupuliform. Spikelets ternate at least in the lower part of the racemes, homomorphous, lanceolate-elliptic, 3–3.2 mm long; apex acute; hairs smooth with clavate apex. Lower glume collar-shaped, ca. 0.3 mm long, membranous, apex truncate. Upper glume elliptic to slightly lanceolate, 2.8–3 mm, chartaceous, apex acuminate, pubescent with overtopping hairs, nerves 3. Lower lemma lanceolate, 3–3.2 mm, chartaceous, apex acute, pubescent between nerves but with narrow glabrous interspaces beside the midnerve, nerves 7; inequidistant. Upper lemma lanceolate, 2.4–2.5 mm, chartaceous, apex acuminate, brown to dark purple. Anthers 1.7–1.8 mm long. Caryopsis ellipsoid, 1.9–2.1 mm long, brownish. ( Figures 5C & 5D )

Distribution: — Sierra Leone, DR Conggo, Ethiopia, Zambia, S Africa, Madagascar, S. China, Myanmar, Thailand, Lao PDR, Vietnam.

Selected specimens examined: —LAO PDR. Xiangkhoang: 19 April 1932, A.F.G. Kerr 21121 (BM, K). MYANMAR. Bago: Taungoo, U T. Lwin 2947 (K). THAILAND. Lampang: Ngao, Mae Huat, 19 December 1956, T. Kokkamhaeng 35 (BKF, K). Phetchabun: Lom Sak, Huai Wa, 10 May 1955, T. Smitinand 2704 (BKF, K). Sakon Nakhon: Phu Phan National Park, 11 June 2009, B. Boonsuk 73 (BK, BKF, KKU, QBG). Chaiyaphum: Thep Sathit, 15 May 2008, M. Norsaengsri 3838 (QBG). VIETNAM. Gia Lai: Ayun Pa, June 1955, M. Schmid s.n. (P).

Ecology: —Dry dipterocarp forest, grasslands; elevation 300–1,000 m.

Conservation status: — Digitaria setifolia is a perennial African species, distributed in China and mainland SE Asia. We designate this species with a status of LC according to IUCN (2012) criteria.

Note: — Digitaria setifolia is a distinctive erect, tufted and rhizomatous species. Its leaf sheaths are usually fibrous at the base and its leaf blades are narrowly linear and very long (30–40 cm long). Hairs on its spikelets are brownish and smooth with clavate apex. There is an interesting disjunction between D. setifolia from Africa and D. fibrosa from Asia because there has no record of them in the Middle East and the subcontinent of India but they could be undercollected. Chen & Phillips (2006) distinguished both species by the characters of leaf blades which are filiform with inrolled margins in D. setifolia but linear and flat in the latter. However, leaf blades of both species are very narrow and we agree that leaf form is not significantly different because it may represent a spectrum of variation or be an adaption for its habitat. Most grass leaves can be inrolled when in drought conditions. Furthermore, both species have leaf sheaths breaking to fibres at the bases and comprise very similar spikelets. Consequently, we accept that both are the same species and D. fibrosa should be a synonym of D. setifolia . Digitaria fibrosa is present in China, Lao PDR, Myanmar and Vietnam ( Camus & Camus 1922, Kress et al. 2003, Chen & Phillips 2006); therefore, this is the first report of D. setifolia for these countries.

Figures

FIGURE 5. SEM micrographs of spikelets of some Digitaria species from mainland SE Asia. A–B. D. radicosa (from B. Boonsuk 216): A. lower glume and lower lemma; B. upper glume. C–D. D. setifolia (from B. Boonsuk 232): C. lower glume and lower lemma; D. upper glume. E–F. D. stricta var. glabrescens (from B. Boonsuk 478): E. lower lemma; F. upper glume and upper lemma. G–H. D. ternata (from B. Boonsuk 330): G. lower glume and lower lemma; H. upper glume. I–J. D. tomentosa (from J.F. Maxwell 05-484): I. lower lemma; J. upper glume and upper lemma. K–L. D. violascens (from B. Boonsuk 297): K. lower lemma; L. upper glume. Scale bar: A–D. & G–J. = 400 μm, E–F. & K–L. = 200 μm.