Ischaemum rugosum Salisb.

Global description
 
Ischaemum rugosum is an annual tufted grass with an erect or geniculate culm and prostrate at the base, branched and rooted at the lower nodes then erected, 20 cm to 1 m high. The leaves are erect or spread, wider in the middle. The lamina is a linear, plane and ends in an acute apex, with variable size, 5 to 25 cm long. The terminal inflorescence is first included in the last leaf and then fully extended. It consists of two golden yellow racemes, closely juxtaposed at 3 to 8 cm long, and then separated and obliquely erected at maturity. The racemes are fake spikelets, with very fragile axis, formed from thick articles that easily dislocate when dry. Each article consists of two spikelets including a sessile one, 4 to 6 mm long, and the other is pedicellate. The lower glume is transversely, strongly undulated with 3-5 convex transverse ridges.
 
First leaves
 
At emergence, Ischaemum rugosum is first recognizable by the remainder of the seed in its envelope, ellipsoid, 3 to 5 mm long, strongly marked by 3 to 5 transverse ridges. The first 2 or 3 leaves have a short sheath and a short blade with a rolled prefoliation. The following leaves lengthen quickly; the lamina 15 to 25 cm long, glabrous, and is carried by a flat sheath, 10 to 15 cm long. Successive sheaths are more or less embedded in each other.
 
General habit
 
Tufted plant with dense clumps, erect stems or prostrate  at the base and then straightened up to 1 m in height.
 
Underground system
 
The roots are fibrous and dense. Presence of adventitious roots from the lower nodes of stem.
 
Culm
 
The cylindrical culm is hairless, with dark hairy nodes, branched and rooted at the lower nodes and then erected, geniculate.
 
Leaf
 
The leaves are simple, alternate. The sheath has a loose pubescence, especially near the margin. The ligule is membranous papery, measuring 3 to 5 mm long. The lamina is a linear plane, erect or spreading, wider toward the middle, very variable in size, 5-25 cm long and 4-8 mm wide, ending in an acute apex, and clear green in colour or frequently pigmented with purple. Both sides are glabrous except for a few long hairs along the main veins. The margin is sharply pectinate.
 
Inflorescence
 
The inflorescence is first included in the last leaf sheath and finally clearly exteriorized, formed by two geminal racemes, at first closely juxtaposed taking  the appearance of a cylindrical erect spike, 3 to 10 cm long, and then separated and obliquely erect. The racemes are formed from thick articles with a line of hairs on its back, disarticulating easily when dry.
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Spikelet
 
Each article is formed by two kinds of spikelets of similar morphology: one is sessile, 4 to 6 mm long, oblong, appressed against the rachis, yellow at the base and to red brown at the top, and the other with a robust pedicel, short and stocky, almost as long as the sessile spikelet. For each spikelet, the lower glume, is the size of the spikelet and is highly wrinkled transversely, muticate or awned and scabrous on the sides. The upper glume is also long but narrower, laterally compressed, and keeled on the back. The lemma of flower is fertile, shorter than the glumes and deeply bifid till the half, with a brown edge in the sinus, angled towards the middle, about 2 cm long.

Grain
 
The grain is ellipsoid, 2 mm long and 1 mm wide, enveloped.
 

Origin

Ischaemum rugosum is native of tropical Asia, West and locally East Africa.

Worldwide distribution

This species has been introduced in Indian Ocean (Madagascar, Comoros), in Central and South America, and also Caribbean islands.

https://www.gbif.org/fr/species/2702462