Plants annual, or short-lived perennials. Culms 30-130 cm, erect
or geniculate at the base, simple to strongly branched below; nodes antrorsely
pilose; internodes glabrous. Leaves cauline; sheaths mostly
glabrous or sparsely pilose, margins ciliate distally; collars villous;
ligules 1-5.5 mm; blades 8-20 cm long, 7-15 mm wide, flat, usually
pilose on both surfaces, sometimes with papillose-based hairs, occasionally glabrous.
Inflorescence units with 2 rames; rames 3-8 cm long, 3-4 mm wide;
internodes 2.5-3.5 mm, slightly clavate distally. Sessile spikelets
3-5 mm long, 1.8-2.2 mm wide; calluses shortly pubescent; lower glumes
coriaceous, yellowish, not winged, coarsely transversely rugose with 4-5 ridges
on the proximal 2/3-4/5, thickly chartaceous distally and tapering to the apices;
upper glumes thickly chartaceous, ciliate, awned, awns 1.5-2 cm, geniculate
below the middle; anthers about 2 mm. Pedicellate spikelets varying
from 0.5 mm to equaling the sessile spikelets. 2n = 18, 20, 44.
Ischaemum rugosum is native to southern Asia, and is now established in
moist, tropical habitats around the world, including Mexico. It has been found
in southern Texas and on chrome ore piles in Canton, Maryland, but is thought
to have been eliminated from both areas. The U.S. Department of Agriculture considers
it a noxious weed; plants found growing within the continental United States should
be promptly reported to that agency.