Digitaria radicosa (J. Presl) Miq. (1857: 437)

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 : 264-265

17. Digitaria radicosa (J. Presl) Miq. (1857: 437) .— Panicum radicosum J. Presl (1830: 297) . Type :— PHILIPPINES, Luzon, T. Haenke s.n. (holotype PR; isotype US-80950 (fragm.)).

Digitaria propinqua Gaudich. (1829: 410) , non D. propinqua (R. BR.) P. Beauv. (1812: 160, 170).— Panicum timorense Kunth (1833: 83) .— D. timorensis (Kunth) Balansa (1890: 138) . — P. sanguinale L. var. timorense Hack. (1901a: 97) .— Paspalum sanguinale Lam. var. timorense A. Camus (1912: 222) . Type:— INDONESIA, Lesser Sunda Islands, Timor, C. Gaudichaud s.n. (holotype P; isotypes L, US).

Digitaria formosana Rendle (1904: 323) . Type :— TAIWAN, A. Henry 1941 (holotype K!; isotypes BM!, P!, W).

Digitaria tenuispica Rendle (1904: 326) . Type:— CHINA, Jiangsu, Shanghai, A.C. Maingay 554 (syntypes BM!, K!, P). Kwantung, Macao, Buchanan-Hamilton s.n. (syntype BM).

Annual. Culms slender, stoloniferous or decumbent, 30–40 cm high, rooting at lower nodes; nodes and internodes glabrous; cataphylls absent. Sheaths 2–3.5 cm long, glabrous. Ligules 1.2–2 mm long. Blades linear, 3.5–6 cm by 2.5– 6 mm, chartaceous, apex acuminate, margin hispid and slightly crenate, upper surface scabrous, lower surface scabrous and sparsely setose. Inflorescences composed of racemes; peduncles glabrous; common axis 0–1 cm long. Racemes 2 or 3, longest 5–8.5 cm long, digitate or subdigitate; rachis ribbon-like, winged, 0.5–0.7 mm wide, margin smooth. Pedicels triquetrous, serrate; abscission truncate. Spikelets binate, homomorphous, lanceolate, 2.8–3.2 mm long; hairs smooth with acute apex. Lower glume triangular, ca. 0.3 mm long, chartaceous, apex acute. Upper glume lanceolate to elliptic, 1.2–1.7 mm long, chartaceous, apex acute, pubescent between nerves and on margins, nerves 3. Lower lemma as long as the spikelet, chartaceous, apex acute to acuminate, pubescent between nerves and on margins but with broad glabrous interspaces beside the midnerve, nerves 7, inequidistant. Upper lemma 2.6–2.8 mm long, chartaceous, apex acuminate, not protruding above the lower lemma, yellowish. Anthers 0.5–0.8 mm long, brown. Caryopsis ellipsoid, 1.4–1.8 mm long, brownish. ( Figures 5A & 5B )

Distribution: —Common, tropical Asia.

Selected specimens examined: — LAO PDR. Xekong: Lamam, 12 October 2010, B. Boonsuk & S. Lanosavanh 438 ( KKU, Biology Herbarium NUOL). MYANMAR. Tanintharyi: 17 October 1998, J. F. Maxwell 98-1146 ( CMU, L). PENINSULAR MALAYSIA. Pahang: 24 April 1931, R. E. Holttum 24733 ( SING). Kuala Lumpur: 20 January 1921, H. L. Hume 7680 ( SING). Terengganu: 17 September 2006, H. Duistermaat & M. Y. Chew FRI 53116 ( KEP, L). THAILAND. Mae Hong Son: Khun Yuam, 16 October 2009, B. Boonsuk 158 ( BK, BKF, KKU, QBG). Sukhothai: Thung Luang , 8 November 1931, A. F. G. Kerr 20593 ( BK, BM, K). Nakhon Phanom: Renu Nakhon , 25 October 2009, B. Boonsuk 175 ( KKU). Khon Kaen: Mueang , 20 February 2010, B. Boonsuk 222 ( BK, BKF, KKU). Nakhon Ratchasima: Thap Chang , 28 July 1994, T. Smitinand 767 ( BKF). Kanchanaburi: 19 October 1930, A. F. G. Kerr 19762 A ( K) ; Nakhon Nayok: 24 November 1957, J. V. Santos 6662 ( L). Chanthaburi: Pong Nam Ron, 28 November 1956, T. Smitinand 3661 ( BKF). VIETNAM. Hanoi: 13 August 1890, B. Balansa 4536 ( P) ; 28 October 1902, D. Bois 552 ( K, P). Dac Lac: Buon Ma Thout, 1 December 1950, M. Schmid 21 ( P). Ho Chi Minh City: 1 November 1954, M. Schmid s.n. ( P) .

Ecology: —Shady areas, weeds in gardens; elevation 200–1,000 m.

Conservation status: — Digitaria radicosa is distributed throughout mainland SE Asia. Therefore, we provide this species with a rating of LC according to IUCN (2012) criteria.

Note: — Digitaria radicosa is distinguished by having slender culms, few racemes, smooth rachis and lanceolate 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.