Digitaria ternata (A. Rich.) 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 : 269-270

22. Digitaria ternata (A. Rich.) Stapf (1898: 376) .— Cynodon ternatus A. Rich. (1851: 405) .— Panicum ternatum (A. Rich.) Hochst. ex Steud. (1853: 40) .— Paspalum ternatum Hook. f (1897: 17).— Syntherisma ternata Newbold (1924: 9) . Type:— ETHIOPIA, G.H.W. Schimper 76 (lectotype P!; isolectotypes B†, K!, L, US), designated by Henrard (1950).

Panicum argyrostachyum Steud. (1853: 40) .— D. argyrostachya (Steud.) Fernald (1920: 103) . Type:— INDONESIA, Java, H. Zollinger

260 (holotype P!; isotypes K!, L!). Digitaria ropalotricha Buse (1854: 381) . Type:— INDONESIA, Java, F.W. Junghuhn s.n. (holotype L!; isotype U). Digitaria ropalotricha var. glabrescens Buse (1854: 381) . Type:— INDONESIA, Java, F.W. Junghuhn s.n. (lectotype L!; isolectotype U),

designated by Henrard (1930: 17).

Annual or perennial. Culms tufted, not rhizomatous, ascending to erect, 35–90 cm high, many leaves at base. Sheaths 5.5–7.5 cm long, glabrous. Ligules 1.5–3 mm long, glabrous. Blades linear, 14–16 cm by 6–8 mm, chartaceous, apex acute, margin serrate; both surfaces glabrous. Inflorescences composed of racemes; common axis 0–2 cm long; peduncles pubescent at terminal. Racemes 4 or 5, longest 12–22 cm long, digitate; rachis ribbon-like, winged, usually straight, 0.6–0.9 mm wide, serrate. Pedicels terete to trigonous, longest pedicels as long as the length of spikelet, with elongate spicules; abscission cupuliform. Spikelets ternate, homomorphous, elliptic, 2.2–2.5 mm long, apex acute, pubescent; hairs smooth with clavate apex. Lower glume 0.2–0.3 mm long, membranous. Upper glume ovate to elliptic, 1.4–1.8 mm long, chartaceous, pubescent between nerves and on margins, nerves 3. Lower lemma elliptic, 2.2–2.5 mm long, chartaceous, apex acute, pubescent with glabrous interspaces beside the midnerve, the interspaces narrower than outsides, nerves 7, inequidistant. Upper lemma 2.2–2.5 mm long, chartaceous, apex acute, dark purplish to blackish. Anthers 0.8–0.9 mm long. Caryopsis ellipsoid, 1.7–2 mm long, creamy. ( Figures 5G & 5H )

Distribution: — South Africa North to Guinea, Ethiopia, India, Sri Lanka, China, Myanmar, Thailand, Lao PDR, Vietnam, Malaysia, Singapore, Indonesia, Philippines, introduced in Papua New Guinea and elsewhere, e.g. Australia, New World.

Selected specimens examined: —LAO PDR. Xiangkhouang: 2 October 1933, A. Pételot 4392 (P). Attapeu: 12 October 2010, B. Boonsuk & S. Lanosavanh 439 (KKU, Biology Herbarium NUOL). Champasak: Paksong, 12 October 2010, B. Boonsuk & S. Lanosavanh 435 (KKU, Biology Herbarium NUOL). MYANMAR. Mandalay: Pyin Oo Lwin, 9 October 1908, J.H. Lace 4292 (K). Bago: Tharrawaddy, 19 September 1947, U T. Lwin 224 (K). Yangon: 3 August 1932, C.E. Parkinson 14697 (K). PENINSULAR MALAYSIA. Pahang: Cameron Highlands, 8 March 2010, R. Kiew, H. Duistermaat & Mohd. Nazri FRI 70413 (KEP, L). THAILAND. Mae Hong Son: Doi Mae U-Kho, 17 October 2009, B. Boonsuk 161 (BK, BKF, KKU). Chiang Mai: Mae Chaem, 15 October 2009, B. Boonsuk 154 (BK, BKF, KKU). Nan: Pua, Doi Phu Kha National Park, 21 September 1989, Y. Paisooksantivatana y-2475-89 (BK). Phitsanulok: Phu Hin Rong Kla National Park, 11 September 2010, B. Boonsuk, P. Phonsena & P. Kochaiphat 411 (KKU). Loei: Phu Ruea National Park, 11 October 2009, B. Boonsuk 148 (BK, BKF, KKU). Kanchanaburi: Thong Pha Phum, 22 September 2009, B. Boonsuk 145 (KKU). Krung Thep Maha Nakhon: 29 August 1958, A.F.G. Kerr 3788 (BK, BM, K). VIETNAM. Dac Lac: 11 November 1998, J.B. Hacker 1599 (L). Ninh Thuan: Phan Rang, 18 September 1854, M. Schmid VN 2368 (P).

Ecology: —Open areas, grasslands, dry dipterocarp and pine forests, mountain slopes; elevation 300–2,000 m.

Conservation status: — Digitaria ternata is widespread and we designate its conservation status as LC according to the IUCN (2012) criteria.

Note: —This species is usually found at high elevations and cool places. Its spikelets are ternate and are arranged on a ribbon-like rachis similar to that of members of section Ischaemum , but the hairs of its spikelets are distinctly clavate. It is similar to D. stricta with its dark purple to blackish upper florets, but it differs in having larger spikelets and an upper glume longer than half the length of the spikelet. This is the first report of D. ternata for the Lao PDR.

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.