Digitaria bicornis

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 : 254-255

3. Digitaria bicornis (Lam.) Roem. & Schult. (1817: 470).— Paspalum bicorne Lam. (1791: 176).— Panicum bicorne Kunth (1829: 33) . Type:— INDIA, P. Sonnerat s.n. in Herb. Lamarck (holotype P, microfiche IDC 6207; isotype US-2854145 (fragm.)).

Digitaria barbata Willd. (1809: 91) .— D. rottleri Roem. & Schult. (1817: 471) .— Panicum barbatum (Willd.) Kunth (1829: 33) .— P. appressum Willd. ex Kunth (1833: 84) , non P. appressum Forssk. (1775: 20) .— Syntherisma barbata (Willd.) Nash (1898: 303) . Type:— INDIA, Klein s.n. (holotype B; isotype K!).

Digitaria biformis Willd. (1809: 92) .— Panicum biforme Kunth (1829: 33) .— P. sanguinale L. var. biforme Hack. ex T. Durand & Schinz (1894: 762) . Type:— MAURITIUS, J.B.G.M. Bory de Saint Vincent s.n. (holotype B! (B-W237260)).

Digitaria commutata Schult.f. (1824: 262) .— Panicum commutatum (Schult.f.) Nees (1832: 274) .— Paspalum sanguinale Lam. var. commutatum Hook.f. (1897: 15) . Type:— INDIA, W. Roxburgh s.n. (holotype BM).

Digitaria corymbosa Merr. subsp. marathensis Henrard (1950: 152) .— D. setigera Roth ex Roem. & Schult. subsp. marathensis (Henrard) Henrard ex Bor (1955: 346) . Type:— A.P. Young s.n. (holotype L!; isotypes BM!, K!).

Annual. Culms not robust, small or loosely tufted, ascending to erect or decumbent, 80–115 cm high, rooting at lower nodes; nodes and internodes glabrous; cataphylls absent. Sheaths setose or glabrous, 5–7 cm long. Ligules 2–2.5 mm long. Blades linear, 12–25 by 8–12 mm, apex acute, margin serrate and sinuate at one side, upper surface scaberulous with sparse setae at base, lower surface scaberulous. Inflorescences composed of racemes; peduncles glabrous; common axis 0(–2) cm long. Racemes 4–7, longest 13–16 cm long, digitate or subdigitate; rachis triquetrous and winged, 0.8– 1 mm wide, serrate. Pedicels triquetrous, serrate; abscission truncate. Spikelets binate, heteromorphous, lanceolate, 3–3.2 mm long; pedicelled spikelets pubescent with sericeous and whitish bristles; sericeous hairs smooth with acute apex. Lower glume triangular, ca. 0.3 mm long, chartaceous, apex acute. Upper glume lanceolate, 2.8–3 mm long, chartaceous, apex acuminate, pubescent between nerves and on margins, nerves 3. Lower lemma of pedicelled spikelets lanceolate, 3–3.2 mm long, chartaceous, apex acute, pubescent between nerves but with broad glabrous interspaces beside the midnerve, composed of sericeous and terete bristles, nerves 7, inequidistant; lower lemma of sessile spikelet slightly pubescent on margins, apex acute, pubescent near the margins or glabrous, nerves 7, equidistant. Upper lemma lanceolate, 2.5–2.8 mm long, chartaceous, apex acute, not protruding above the lower lemma, yellowish to brownish. Anthers 1–1.2 mm long. Caryopsis oblong-ellipsoid, ca. 2 mm long, brownish. ( Figures 3E–3H )

Distribution: —Common, tropical and subtropical regions.

Selected specimens examined: —LAO PDR. Vientiane: Pak Ngum, 26 June 2010, B. Boonsuk & S. Lanosavanh 300 (KKU, Biology Herbarium NUOL). Xé Kong. 12 October 2010, B. Boonsuk & S. Lanosavanh 437 (KKU, Biology Herbarium NUOL). Attapeu: 12 October 2010, B. Boonsuk & S. Lanosavanh 440 (KKU, Biology Herbarium NUOL). MYANMAR. Yangon: Yegu, 10 April 1932, C.E. Parkinson 15181 (K). Rakhine: Ramree Island, September 1945, E.L. Wallace 9010 (K). PENISULAR MALAYSIA. Kedah: Langkawi, E.J.H. Corner & J.C. Nauen SF 38111 (B, K, SING). Penang: 15 September 1921, M. Nur Bin Mohamed Ghose 6449 (BO). THAILAND. Chiang Rai: Chiang Saen, 16 July 2010, B. Boonsuk 331 (KKU). Nakhon Sawan: 21 July 1973, G. Murata, N. Fukuoda & C. Phengklai T-16578 (BKF, L). Mukdahan: Phu Pha Thoeb National Park, 13 May 1932, A.F.G. Kerr 21423 (BK, BM, K). Ubon Ratchathani: Sirinthon, Khan Rai, 26 July 2010, B. Boonsuk 341 (BK, BKF, KKU, QBG). Kanchanaburi: Thong Pha Phum, 6 February 1962, K. Larsen 9624 (C). Rayong: Klaeng, Chak Pong, 18 November 2008, P. Wassumrit & M. Norsaengsri 134 (QBG). Songkhla: Ko Yo, 14 August 2010, B. Boonsuk 356 (KKU). VIETNAM. Thanh Hóa: 11 August 1892, R.P. Bon 5559 (P). Quảng Ngãi: A. Pételot 5614 (P). Ho Chi Minh City: 21 January 1869, E. Lefèvre 470 (P). Biên Hòa: June 1929, Ch. D’Alleizette s.n (L).

Ecology: —Open areas; elevation up to 400 m.

Conservation status: — Digitaria bicornis is common and widespread throughout tropical and subtropical regions. Therefore, we classify this species with the rating of LC, according to IUCN (2012) criteria.

Note: — Digitaria bicornis has heteromorphous spikelets. The sessile spikelets are slightly smaller than the pedicelled ones. The whitish sericeous hairs mixed with bristles, patent at maturity on the lower lemma of the pedicelled spikelets are quite diagnostic.

Figures

FIGURE 3. SEM micrographs of spikelets of some Digitaria species from mainland SE Asia. A–B. D. abludens (from S. Laegaard & M. Norsangsri 21666): A. lower lemma; B. upper glume. C–D. D. fuscescens (from B. Boonsuk 627): C. lower lemma; D. upper glume. E–H. D. bicornis (from B. Boonsuk 341): E–F. subsessile spikelets; E. lower glume and lower lemma; F. upper glume. G–H. pedicelled spikelets; G. lower glume and lower lemma, sericeous hairs and bristles on lower lemma; H. upper glume. I–J. D. ciliaris (from B. Boonsuk 375): I. lower glume and lower lemma; J. upper glume. K–L. D. nuda (from B. Boonsuk 286): K. lower glume; L. upper glume. Scale bar: A–D = 200 μm, E–L = 400 μm.