Digitaria costaricensis R.W. Pohl, 1976

Sánchez-Ken, J. Gabriel, 2017, Digitaria clarkiae (Paniceae, Panicoideae, Poaceae), a new species with a paniculate synflorescence, and the first record of D. costaricensis from México, Phytotaxa 321 (1), pp. 125-138 : 131-134

Digitaria costaricensis R.W. Pohl

Type: — COSTA RICA. Cártago: 25 km S of El Tejar along the carretera interamericana, [09º45’ N, 83º45’ W], roadside ditch, 1780 m, 8 October 1968, R. W. Pohl & G. Davidse 11215 (holotype ISC!, isotypes CR, F!, K!, L, MO, UC, US!).

Plants perennial, flowering culms up to 1 m tall, long decumbent, rooting at the nodes, sometimes becoming buried and appearing rhizomatous, when not buried stoloniferous, sward forming; internodes 4.5–13 cm long below the synflorescence, shorter than the leaf sheaths, branching along the prostrate culm, glabrous, but with scattered papillose long-hairs in young culms; nodes brown, the lower ones hirsute becoming glabrous towards the synflorescence; sheaths shorter or longer than the internodes, those of the prostrate culm densely papillose-hirsute, those of the fertile culms glabrous or with scattered papillose long-hairs at the base; collar broad, yellowish; ligules 1.5–3 mm long, membranous, glabrous, sometimes the edges separating like auricles, apex erose; blades 6–11(–15) cm × 3–7(–9) mm, the lower ones much shorter, lanceolate, thick, glaucous, those of the vegetative culms densely papillose long-pilose on both surfaces, more toward the base, those of fertile culms only scabrous on both surfaces or with scattered papillose long-hairs, midvein thickened and yellow, margins scabrous, base slightly attenuate, apex acute; synflorescence 7–16 cm long, axillary, exserted, not breaking up at maturity; primary branches 4–7, 9–14 cm long, along an short axis, lowermost appear semi-verticillate then alternate, with spikelets at the base, paired on a short axis, somewhat remote, rarely lowermost solitary when one is reduced or absent, remaining only the pedicel, rachis triquetrous, without pulvini; pedicels 0.4–0.9 mm long the shorter ones, 2–2.5(–3.5) mm longer ones, capillary, scabrous; spikelets homomorphic, 3.2–4.1 × 0.85–1 mm, elliptic to slightly lanceolate; first glume nearly absent or a cuff-like membrane up to 0.1–0.3 mm long, truncate, glabrous, veinless, separated of the second glume; second glume as long as the spikelet, 5–7-veined, short-pilose with the hairs forming a stripe in the spaces between veins and margins, the hairs up to 0.5 mm long, white to black, apex acute, usually reaching or slightly exceeding the apex of the fertile lemma; sterile lemma as long as the spikelet, 7–9-veined, the veins nearly equally spaced, central interspaces slightly wider, central interspaces glabrous, the next interspaces short-pilose, the next glabrous and then the margins short-pilose, the hairs forming a stripe, hairs up to 0.4 mm long, white to black, apex acute; sterile palea up to 0.2 mm long, hyaline, glabrous; sterile lodicules as long as the sterile palea; fertile lemma 3–3.3 × 0.8–0.9 mm, lanceolate to elliptic, cartilaginous, pale green to bluish or grayish, softly papillose, glabrous, 3-veined, margins membranous, apex acuminate nearly beak-like; fertile palea as long as and similar to the fertile lemma, glabrous, 2-veined, apex acute; lodicules 2, minute, fleshy; stamens 3, anthers 0.9–1.6 mm long; caryopsis up to 3.4 mm × ca. 1 mm, oblong-elliptic, slightly flattened, yellowish, hilum ca. 2/7 as long as the embryo, oblong, embryo ca. 1/3 as long as the caryopsis.

Distribution and Habitat: —The species is recorded from México (Veracruz) ( Fig. 5 ), Guatemala, San Salvador, Costa Rica and Venezuela ( Vega & Rúgolo de Agrasar 2005, 2007, www.tropicos.org). Apparently common in roadside ditches or near to marshes, at elevations from sea level to 1780 m.

Specimen Examined: — MÉXICO. Veracruz: Mpio. Tecolutla, Paso del río Riachuelos, dunas, 0 m, 4 May 1983, Brigada de dunas 1902 (MEXU).

Related Species: — Digitaria costaricensis , a species variously classified in sections Aequiglumae Henrard (1950: 641) or Debiles ( Clayton & Renvoize 1986: 299), is a new record for México in the state of Veracruz, known from a single collection. Whether it is a native or introduced in Veracruz is unknown. Section Debiles is characterized by having a perennial habit, rachis of the primary branches triquetrous, first glume typically absent or minute, and the most distinctive character is the length of the second glume, which is as long as the spikelet and sterile lemma ( Webster & Hatch 1990). Of the twelve known species of sect. Debiles , six are known from South America [ D. aequiglumis (Hackel & Arechavaleta in Arechavaleta 1894: 113) Parodi (1922: 47), D. connivens ( Trinius 1835: 206) Henrard (1930: 6) , D. costaricensis , D. cuyabensis ( Trinius 1835: 206) Parodi (1926: 378) , D. eriostachya Mez (1921: 80) , D. lanuginosa ( Nees 1829: 63) Henrard (1930: 5) and D. sabulicola Henrard (1934: 108) ], three from Central America [ D. costaricensis , D. cuyabensis and D. leucites ( Trinius 1826: 85) Henrard (1930: 6) ], one from Cuba [ D. ekmannii Hitchcock (1936: 176) ], three from the United States [ D. pauciflora Hitchcock (1928: 162) , D. simpsonii ( Vasey 1892: 25) Fernald (1920: 103) and D. texana Hitchcock (1928: 162) ], and three are now known from México [ D. costaricensis , D. leucites and D. texana ]. Digitaria aequiglumis is a weedy species that has been introduced in Europe, Australia ( Lepschi & Macfarlane 1997, Aniotshbérhère 2002) and possibly elsewhere. Nearly two and a half decades ago, D. costaricensis was known only from the type locality ( Pohl & Davidse 1994), but since then, its range has expanded from México to Venezuela.

The presence of D. costaricensis and the new species D. clarkiae increases the number of species of Digitaria in México from 31 to 33 ( Sánchez-Ken 2012).

Figures

FIGURE 5. Distribution of Digitaria clarkiae (solid black rhomboids) in Guerrero, Morelos and Puebla, and of D. costaricensis in Veracruz (solid black circle).