Digitaria violascens Link (1827: 229)

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 : 272-273

27. Digitaria violascens Link (1827: 229) . Type:— BRASIL, J.H.F. Link 93 (holotype B! (B100185495)).

Paspalum chinense Nees ex Hook. & Arn. (1837: 231) .— D. chinensis (Nees ex Hook. & Arn.) A. Camus (1923: 48) , non D. chinensis

Hornem. (1819: 8). Type:— CHINA, Guangdong, G.H. Vachell s.n. (holotype CAM; isotype CGE). Digitaria digitata Buse (1854: 341) . Type:— INDONESIA, Java, F.W. Junghuhn s.n. (holotype L!; isotype U). Digitaria pertenuis Buse (1854: 341) . Type:— INDONESIA, Sumatra, F.W. Junghuhn s.n. (lectotype L!; isotype U), designated by

Veldkamp (1973). Digitaria caespitosa Ridl. (1925: 215) . Type:— SINGAPORE, H.N. Ridley s.n. (lectotype K!), designated by Veldkamp (1973). Digitaria bogoriensis Ohwi (1947: 5) . Type:— INDONESIA, Java, J. Ohwi 15 (holotype BO!; isotypes K! (fragm. in BRI), L!).

Annual or perennial. Culms tufted, not rhizomatous, 25–35 cm high, glabrous, nodes glabrous. Sheaths glabrous, 4–7 cm long, usually longer than internodes, purple-greenish. Ligules 1.5–2 mm long. Blades linear, 5–17 cm by 3–5 mm, chartaceous, apex acuminate, margin entire to minutely scabrous; both surfaces glabrous. Inflorescences composed of racemes; peduncles glabrous; common axis 0.3–3 cm long. Racemes 2–7, longest 5–12 cm long digitate or subdigitate; rachis ribbon-like, winged, usually straight, 0.9–1 mm wide, serrate. Pedicels terete, with minute spicules; abscission cupuliform. Spikelets ternate, homomorphous, elliptic, 1.4–1.8 mm long, apex acute; hairs verrucose. Lower glume absent or minute, membranous. Upper glume lanceolate, 1.2–1.6 mm long, chartaceous, apex acute, pubescent between nerves, nerves 3. Lower lemma elliptic, as long as the spikelets, chartaceous, apex acute, pubescent between nerves and on margins with narrow glabrous interspaces beside the midnerve, nerves 5–7, inequidistant. Upper lemma 1.3–1.7 mm long, chartaceous, apex acute, dark brown to purple. Anthers 0.3–0.5 mm long, yellowish. Caryopsis broadly ellipsoid, 0.9–1 mm long, creamy. ( Figures 5K & 5L )

Distribution: —Common, tropics and subtropics of America, Asia, Australia.

Selected specimens examined: —PENINSULAR MALAYSIA. Kedah: Kampong Naka, 19 September 1933, R.E. Holttum SF 19839 (K, P, SING). Malacca: 17 July 1956 H.B. Gilliland 5122 (SING). Perak: 5 March 1924, I.H. Burkill SF 12653 (K, SING). Terengganu: Dungun, 25 September 2006, T.L. Yao, H. Duistermaat, R. Kiew & H.L. Kueh FRI 53054 (KEP, L). THAILAND. Uttaradit: Phu Soi Dao National Park, 19 November 2009, M. Norsaengsri & S. Intamusik 6262 (QBG). Nakhon Phanom: Tha Uthen, 8 May 1932, A.F.G. Kerr 21370 (BK, BM, K). Nakhon Ratchasima: 15 March 1958, Th. SØrensen, K. Larsen & B. Hansen 2126 (BKF, K). Satun: Khuan Don, 28 February 2012, B. Boonsuk 623 (BKF, KKU). Songkhla: Hat Yai, PSU, 1 April 2012, B. Boonsuk 629 (KKU). LAO PDR. Vientiane: Pak Ngum, 26 June 2010, B. Boonsuk & S. Lanosavanh 297 (KKU, Biology Herbarium NUOL). Champasak: Paksong, 12 October 2010, B. Boonsuk & S. Lanosavanh 436 (KKU, Biology Herbarium NUOL). VIETNAM. Hanoi: 7 June 1887, B. Balansa 1660 (L, P). Quang Ninh: Ha Coi, 23 June 1939, W.T. Tsang 29273 (K, P). Vinh Phuc: 4 December 2010, B. Boonsuk 502 (KKU). Lam Dong: April 1954, M. Schmid 1740 (P).

Ecology: —Open areas, along roadsides; elevation 300–2,400 m.

Conservation status: — Digitaria violascens is very common and has a widespread distribution. Therefore, we classify this species in the category of LC according to IUCN (2012) criteria.

Note: — Digitaria violascens is very similar to D. longiflora . Nanakorn & Norsaengsri (2001) listed this species as a synonym of D. longiflora . However, it differs in having longer leaves, common axis and brown to dark brown upper florets. Veldkamp (1973) pointed out that D. violascens comprises two forms of spikelets: small spikelets and larger spikelets. The small spikelet form is the most common and the larger one is similar to D. thwaitesii var. tonkinensis but differs in having an annual habit without rhizomes and slightly smaller spikelets.

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.