Plants annual or perennial; usually cespitose, rarely stoloniferous. Culms 30-310 cm, erect. Leaves not aromatic; sheaths open; ligules membranous, sometimes ciliate. Inflorescences numerous, terminal and axillary, false panicles; peduncles shorter than the subtending sheaths, with 1-8 rames; rames spikelet-bearing to the base, axes slender, without a longitudinal translucent groove, with 2 large, solitary, homogamous sessile-pedicellate spikelet pairs at the base and 1-4 smaller, heterogamous sessile-pedicellate spikelet pairs distally, terminal or only unit sometimes a triplet with 1 sessile and 2 pedicellate spikelets; disarticulation in the rames below the sessile spikelets of the heterogamous spikelet units, occasionally beneath the homogamous spikelets. Homogamous spikelet pairs distinctive, forming an involucre around the rame bases, separated by internodes less than 1/2 as long as the spikelets; spikelets subequal, strongly compressed dorsally, staminate or sterile, unawned; lower glumes membranous, 2-keeled. Heterogamous spikelet pairs: sessile spikelets subterete or dorsally compressed, awned; calluses bearded, usually sharp; glumes coriaceous; lower glumes wrapped around and concealing the upper glumes, obscurely veined but not keeled, truncate; upper glumes sulcate, with thin margins; lower florets highly reduced, sterile; upper florets bisexual, upper lemmas usually terminating in a geniculate awn; awns usually present, to 9 cm, puberulent to pubescent, sometimes absent. Pedicels slender, not sulcate, not fused to the rame axes; pedicellate spikelets similar to the homogamous spikelets except narrower, staminate or sterile, and unawned. Caryopses narrowly ovate or linear, subterete or channeled on 1 side. x = 5, 10. Name from the Arabic thaemed, a depression where water collects after rain and later evaporates, referring to the habitat of some species of this genus.

Themeda is a genus of approximately 18 species, all of which are native to tropical and subtropical regions of the Eastern Hemisphere, primarily southeast Asia. One species has become established in the Flora region, one is grown as an ornamental, and a third was introduced but is not known to be established.

1.   Themeda arguens (L.) Hack.
Christmas Grass

Plants annual. Culms 1-3 m, erect, or geniculate and ascending. Sheaths glabrous, not flattened at the base. False panicles 20-100 cm; sheaths subtending the rame clusters 35-40 mm, pilose, hairs papillose-based; rames 3-5 per cluster, with 2-3 heterogamous spikelets. Homogamous spikelets 8-10 mm; lower glumes glabrous, acuminate. Heterogamous sessile spikelets 9-11 mm; calluses 3-4 mm; lower glumes hispid and tuberculate-scabrous, dark brown; awns 7-9 cm; pedicellate spikelets 8-10 mm. 2n = 20.

Themeda arguens is native to northern Australia and southeastern Asia. Reed (1964) reported finding it on ore piles in Maryland and Virginia.

2.   Themeda quadrivalvis (L.) Kuntze
Kangaroo Grass

Plants annual. Culms to 2 m, glabrous. Sheaths glabrous, flattened at the base; ligules 1-2.5 mm; blades to 60 cm long, 1-6 mm wide, usually folded. False panicles to 130 cm; sheaths subtending the rame clusters 17-50 mm, distal sheaths shorter and more strongly keeled, margins tuberculate; rames 1-3 per cluster, 8-10 mm, with 1-2 heterogamous spikelet pairs. Homogamous spikelets 4-7 mm; lower glumes many-veined, hairy distally, hairs papillose-based; upper glumes subequal to the lower glumes, 3-veined. Sessile heterogamous spikelets 4-6 mm; calluses 0.5-3 mm; lower glumes glabrous or sparsely hirsute; upper glumes 4.5-5.5 mm; awns 4-5 cm; pedicellate spikelets 4.5-5.5 mm, sterile. 2n = 18.

A native of Malaysia, Themeda quadrivalvis has been found at scattered locations in the contiguous United States. It is established in St. Landry and Iberia Parishes, Louisiana, in addition to having escaped from cultivation in Florida (Baird and Thieret 1985). [I regret that I had not come across Baird and Thieret's article when I prepared this account, as I stated then that "so far as is known, the species is not established in the Flora region." Mary Barkworth, April 13, 2005.] Towne and Ballard (2002) reported that it is a common contaminant of the thistle seed sold for bird feeders. Most of the seeds are sterile, but a few are not.

3.   Themeda triandra Forssk.
Rooigras

Plants perennial. Culms 30-300 cm, erect. Blades to 30 cm long, 1-8 mm wide. False panicles 20-50 cm; sheaths subtending the rame clusters 1.5-3.5 cm, reddish, glabrous or pilose, hairs papillose-based; rames 15-20 mm, with 1 heterogamous spikelet pair. Homogamous spikelets 6-14 mm, glabrous or with papillose-based hairs. Sessile heterogamous spikelets 6-14 mm; calluses 2-4 mm, with rufous hairs; lower glumes mostly smooth, glabrous, apices appressed-pubescent; awns 2.5-7 cm; pedicellate spikelets 6-14 mm, glabrous or with papillose-based hairs. 2n = 20, 21, 22, 24, 40, 60, 70, 80.

Themeda triandra is native to India, Korea, China, and Japan. Many infraspecific taxa have been described in T. triandra and in T. australis (R. Br.) Stapf, a species that is sometimes included in T. triandra. Themeda triandra subsp. japonica (Willd.) T. Koyama is sold as an ornamental in the Flora region but, in the absence of a treatment that covers both species throughout their range, it is impossible to state how it differs from other members of the complex.