Themeda quadrivalvis (L.) Kuntze

Global description
 
Themeda quadrivalvis is a large annual herb in loose upright tufts, reaching 1.50 cm high. The grass stems are erect or geniculate at base, more or less robust, glabrous, branched at the upper nodes. The leaves are glaucous green and become reddish-brown when dry; they have a compressed keeled glabrous sheath and a linear lamina, reaching up to 30 cm long, more or less folded along the midrib, often having a few stiff pectinate hairs at the base of the margins. The inflorescence is a massive, leafy, layered panicle, of quite variable development, 15 to 50 cm long, at the end of a small ramification of the stem. The element of the inflorescence consists of a short raceme subtended by a linear tapered leaf piece at its top, 12 to 20 mm long, green or very often reddish brown. The spikelets are extensively lined with stiff bristles and are extended by a strong geniculate brown edge.
 
First leaves
 
First leaves with folded prefoliation, giving a distichous arrangement to the first leaves. The sheath is glabrous, compressed, keeled. The ligule is membranous truncate. The lamina is erect, folded, and glabrous. The base of the margin is provided with long setaceous pectinate hairs.
 
General habit
 
Grass quite robust, in loose erect tufts, 20 cm to 1.50 m high.
 
Underground system
 
Dense fibrous roots.
 
Culm
 
Compressed culm, erect or geniculate at base, small to moderately robust, glabrous, branched at the upper nodes. The nodes are glabrous.
 
Leaf
 
Leaves are simple, alternate, in distichous arrangement, glaucous green in colour, becoming reddish brown upon drying. The sheath is compressed, keeled, and glabrous. The ligule is membranous truncate or rounded, approximately 3 mm high. The lamina is linear, more or less folded along the midrib, 10 to 30 cm long and 3 to 8 mm wide, glabrous on both sides. The base of the margin is provided with long stiff setaceous, pectinate hairs, with tuberculate base.
 
Inflorescence
 
The inflorescence is a leafy panicle, ranging from 15 to 50 cm in length, interrupted, simple or consisting of several partial inflorescences in the axils of upper leaves, sometimes more complex. The element of the inflorescence is formed of a short raceme, subtended by a linear spatheole, 12 to 20 mm long, acuminate at its top, pectinate at the base of the margin, green or very often red brown in colour.
 
Spikelet
 
The raceme is formed at the base of 2 pairs of similar, sub sessile, closely oblong spikelets, 5 to 6 mm long, sterile, persistent and forming a kind of involucre, with lower glume carrying at its top setaceous stiff hairs with tuberculate base, then 3 spikelets of which one is sessile, fertile and the two others are pedicellate and sterile. The sessile spikelet is cylindrical, 4 to 5 mm long, light brown or dark brown, with lower glume pubescent and rounded on the back, with lemma entire at the top and provided with a strong brown geniculate edge , 3, 5 to 4.5 cm long. The pedicellate spikelets are narrowly lanceolate, glabrous, 4 to 4.5 mm long.
 
Grain
 
Grain linear lanceolate, grooved on one side.

Worldwide distribution

It has been introduced and is considered invasive in Queensland and the Northern Territories of Australia, New Caledonia and Pacific Islands. It is also present in the Idian Ocean islands (Reunion, Mauritius and Madagascar), but also in Thailand, China, Indonesia Papua New Guinea and tropical America.

https://www.gbif.org/fr/species/2703469