Digitaria heterantha (Hook.f.) Merr. (1923: 54)

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 : 258-260

8. Digitaria heterantha (Hook.f.) Merr. (1923: 54) . — Paspalum heteranthum Hook.f. (1897: 16) , pro. comb. — D. dispar Henrard (1934: 97) , nom. superfl. Type:— INDIA, F.J.F. Meyen s.n. (holotype B†; isotype US).

Digitaria baliensis Ohwi (1947: 5) . D. heterantha subsp. aequabilis Henrard (1950: 811) . Type:— INDONESIA, Bali prope Java, Gilimanoch, C. G. G. J. van Steenis 7605 (holotype BO!; isotype L!)

Digitaria bantamensis Ohwi (1947: 5) .— D. heterantha var. holosericea Henrard (1950: 813) . Type:— INDONESIA, Java, C.A. Backer 1609 (holotype BO!; isotypes K!, L).

Digitaria heterantha var. pachyrachis (Hack.) Merr.(1923:54) .— D.heterantha var. pachyrachis Hack.(1908:167) . Type :— PHILIPPINES, Lumbacan Island, E. D. Merrill 5276 (lectotype W! ( W19160021729 ); isolectotypes B! ( B100272562 ), P!, US), designated by Veldkamp (1973)

Digitaria longissima Mez (1922: 26) . Type:— PAPUA NEW GUINEA, New Ireland, G. Peekel 301 (holotype B! ( B100272561 ); isotype US).

Perennial. Culms tufted and creeping, 30–80 cm high. Sheaths 13–17 cm long, setose on lower parts and margins. Ligules 1.5–3 mm long. Blades linear to lanceolate, 3–10 cm by 2–4 mm, chartaceous, upper surface glabrous with bulbose based hairs at base, lower surface scabrous, or both surfaces tomentose, apex acute. Inflorescences composed of racemes; peduncles glabrous; common axis 0–10 cm long. Racemes 2–3, longest 7.5–16 cm long, digitate; rachis triquetrous and winged, serrulate to entire, 0.8–1 mm wide. Pedicels triquetrous, serrate; abscission truncate. Spikelets binate, heteromorphous. Pedicelled spikelets lanceolate, 4.2–5.5 mm long, pubescent with sericeous and setaceous hairs, sericeous hairs smooth with acute apex. Lower glume triangular to oblong, ca. 0.3 mm long, membranous, apex obtuse. Upper glume lanceolate, slightly shorter than spikelets, chartaceous, apex acute, pubescent throughout with sericeous hairs and glassy bristles. Lower lemma lanceolate, as long as the spikelet, chartaceous, apex acute, pubescent throughout with sericeous and flattened setaceous hairs, nerves 9–11, closed and equidistant, making slit-like interspaces. Upper lemma lanceolate, 3–3.5 mm long, chartaceous, brownish. Subsessile spikelets lanceolate, 3.5–3.7 mm long, usually glabrous or pubescent along the margins of upper glume and lower lemma. Anthers 1–1.2 mm long, brownish. Caryopsis oblong-ellipsoid, 1.7–1.9 mm long, creamy. ( Figures 4A–4D )

Distribution: — China, Hong Kong, Thailand, Vietnam, Malaysia, Indonesia, Philippines, Papua New Guinea, perhaps introduced in Australia.

Selected specimens examined: —PENINSULAR MALAYSIA. Pahang: 17 June 1932, E.J.H. Corner SF 225807 (K, BO, SING). THAILAND. Khon Kaen: Nong Song Hong, 26 October 2007, M. Norsaengsri 2827 (QBG). Nakhon Ratchasima: Dan Khun Thot, 22 January 1931, A.F.G. Kerr 19926 (BK, BM, K, L). Prachuap Kiri Khan: Hua Hin, 4 November 1927, A.F.G. Kerr 13419 (BK, BM, K, L). Chanthaburi: Laem Sing, 17 November 1926, Nai Nue 134 (K). Surat Thani: Ko Samui, 11 April 1927, A.F.G. Kerr 12632 (BK, BM, K, L). VIETNAM. Da Nang: 19 January 1903,

D. Bois 686 (K, P); 1 June 1927, J. & M. S. Clemens 4478 ( P). Binh Dinh: Quy Nhõn, 27 December 1886, B. Balansa s.n. ( L). Thua Thien-Hue: 20 October 1909, M. Bauche 116 ( P). Ba Ria–Vung Tau: Vung Tau, M. Schmid s.n. ( P) .

Ecology: —Salty soil, sandy soil on beaches; elevation 5– 150 m.

Conservation status: — Digitaria heterantha is widespread from China to SE Asia. Its conservation status is assessed as LC according to IUCN (2012) criteria.

Note: —The distinguishing characteristics of this species are its heteromorphous spikelets with close-set nerves and slit-like interspaces on the lower lemma. It is similar to D. bicornis but differs in its longer racemes and spikelets and also in flattened bristles on the lower lemma of the pedicelled spikelets ( Fig. 2F ).

Figures

FIGURE 2. SEM photographs of hairs on spikelets of Digitaria species in mainland SE Asia. A. smooth hairs with acute apex (D. nuda). B. verrucose hairs with acute apex (D. thwaitesii var. tonkinensis). C–D. smooth hairs with clavate apex; C. D. abludens. D. D. ternata. E–F. sericeous hairs and bristles. E. bristles terete (D. bicornis). F. bristles flattened (D. heterantha). Scale bar: A–B = 20 μm, C–D = 50 μm, E–F = 100 μm.

FIGURE 4. SEM micrographs of spikelets of some Digitaria species from mainland SE Asia. A–D. D. heterantha (from M. Norsaengsri 2827): A–B. subsessile spikelets; A. lower glume and lower lemma, lower lemma with closed nerves and slit-like interspaces between nerves; B. upper glume. C–D. pedicelled spikelets; C. lower glume and lower lemma, lower lemma pubescent with sericeous hairs and bristles; D. upper glume. E–F. D. longiflora (from B. Boonsuk 370): E. lower glume and lower lemma; F. upper glume. G–H. D. mollicoma (from B. Boonsuk 164): G. lower glume and lower lemma; H. upper glume. I–J. D. petelotii (from B. Boonsuk 98): I. lower glume and lower lemma; J. upper glume. K–L. D. pusilla (from A.F.G. Kerr 11198): K. lower glume and lower lemma; L. upper glume. Scale bar: A–D. & G–J. = 400 μm, E–F. & K–L. = 200 μm.