Digitaria insularis (L.) Mez ex Ekman

Global description

Digitaria insularis is an erect, vivacious clumping grass. Culms are branching at lower and middle nodes, with a swollen base and glabrous nodes. The lower sheaths are usually pubescent, the ligule is membranous, the blade is linear and scabrous. The inflorescence is a large panicle consisting of numerous linear, erect or drooping, very hairy, tan-coloured racemes. The spikelets are arranged in pairs, lanceolate, densely covered with long brown or whitish hairs.

General habit

Digitaria insularis is a large, clumping grass with multiple, upright culms. It is 0.8 to 1.5 m high.

Underground system

The roots are fasciculated, with short and branched rhizomes with tuberculate buds

Culm

The culm is cylindrical, 5-10 mm in diameter and 80-150 cm high. It is erect, rapidly branching at the lower nodes. The nodes are glabrous and have a slight constriction just below.

Leaf

The sheath is cylindrical, abundantly and finely longitudinally striated, it can be glabrous, long ciliated with long white hairs along the margin or abundantly hairy. The ligule is membranous, 2 to 6 mm high. The leaf blade is linear, 12 to 50 cm long and 7 to 20 mm wide. The apex is acuminate and the base is in the extension of the margin of the blade. Both sides are glabrous or slightly scabrous, the margin is scabrous, the main vein is prominent on the lower side and numerous parallel secondary veins are visible.

Inflorescence

The inflorescence is a large panicle composed of 20 to 50 linear racemes, 10 to 15 cm long and distributed along an angular but not winged central rachis, 8 to 30 cm long. The racemes are unilateral, erect or spreading with a drooping tip. They are profusely hairy with long tan to light brown hairs.

Spikelet

The spikelets are in pairs, one carried by a long pedicel of 4 mm, the other carried by a short pedicel of 1 mm. The spikelet is lanceolate, dorsally compressed and long acuminate, 3.5 to 4 mm long and 0.8 to 1 mm wide. The lower glume is oblong, 0.5 to 1 mm long (1/4 the length of the spikelet), hyaline with no keel or venation and a truncated apex. The upper glume is lanceolate with an acuminate apex, as long as the spikelet, membranous with 3 veins, covered with very long and abundant tawny hairs 2 to 4 mm long.
The lower sterile floret is a lanceolate lemma with an acuminate apex, as long as the spikelet, membranous with 7 veins and abundantly covered with long tawny hairs. The palea is absent.
The upper fertile floret is composed of a 3 to 3.5 mm long lanceolate lemma with an acuminate apex, cartilaginous, dark brown, very finely reticulate, with a thinner, membranous and lighter margin, partly covering the palaea. The palaea is cartilaginous, dark brown and finely reticulated.
The spikelet is falling entire at maturity.

Grain

The grain is included in the spikelet and is fusiform, 2.5 to 2.8 mm long.

Origin

Digitaria insularis is native to tropical America (Central America, Caribbean and South America).

Worldwide distribution

This species has been introduced in West Africa (Ivory Coast), Oceania (Philippines, New Guinea, Marquesas, Marianas and Hawaii)

https://www.gbif.org/species/5289938