Plants perennial. Culms to 150 cm, erect or decumbent, rooting at the nodes, usually branched above the bases. Leaves not aromatic; sheaths mostly glabrous, sometimes ciliate near the base; ligules membranous, ciliate; blades usually linear-lanceolate, sometimes linear. Inflorescences terminal and axillary, with 1(2) flattened rames borne on a common peduncle, spikelets partially embedded in the rame axes; disarticulation in the rames, usually oblique and often tardy. Spikelets in heterogamous sessile-pedicellate pairs, dorsally compressed. Sessile spikelets with 2 florets; calluses blunt; lower glumes coriaceous, smooth; upper glumes equaling the lower glumes, chartaceous to membranous, sometimes partially adnate to the rame axes, sometimes awned; lower florets reduced to hyaline lemmas; upper florets bisexual, lemmas unawned. Pedicels thick, fused to the rame axes. Pedicellate spikelets morphologically similar to the sessile spikelets, staminate or sterile. x = 9, 10. Name from the Greek hemi, half, and arthron, segment, because of the tardily disarticulating rames.

Hemarthria is a genus of 12 species, native to the tropics and subtropics of the Eastern Hemisphere, and possibly to the Western Hemisphere. All the species grow in or near water. One species has been introduced into the Flora region.

1.   Hemarthria altissima (Poir.) Stapf & C.E. Hubb.

Plants perennial; rhizomatous and/or stoloniferous. Culms 30-150 cm, erect to ascending, flattened. Leaves basal and cauline; sheaths mostly glabrous, margins sparsely ciliate basally, scabrous distally; ligules 0.2-1 mm; blades flat to conduplicate, glabrous, margins ciliate basally. Rames 2-10 cm, erect. Sessile spikelets: lower glumes 4-5 mm, 10-15-veined, lateral veins distinct, margins scarious, apices acute; upper glumes smooth, hyaline to membranous, acute; anthers 3. Pedicels 4-5 mm. Pedicellate spikelets 4-7 mm, acuminate. 2n = 20, 36.

Hemarthria altissima grows in tropical and subtropical regions throughout the world, including southern Texas and Florida. It is considered native to the Mediterranean region. Although an excellent forage grass, it is not sufficiently abundant in the Flora region to be important in this regard.