Description from Flora of China
Gymnotrix P. Beauvois.
Annuals or perennials. Culms tufted or rhizomatous, prostrate to over 3 m tall. Leaf blades flat, folded or convolute; ligule a ciliate membrane. Inflorescence a spikelike panicle, cylindrical to subglobose; branches numerous, contracted into short clusters of one or more spikelets subtended by an involucre of bristles; involucres sessile or with a short basal stipe, deciduous with the spikelets at maturity leaving peduncle stumps or scars on the main axis; bristles slender, scabrous, sometimes plumose, simple or very rarely branched, very unequal, outer shorter, often innermost stouter and conspicuously exceeding the rest. Spikelets usually lanceolate, dorsally compressed, herbaceous, acute or obtuse, florets 2, glumes and lower lemma variable; glumes often small and not exceeding 1/2 spikelet length; lower lemma staminate or neuter, equaling spikelet or reduced; upper lemma equaling spikelet, herbaceous or indurated, obtuse to acute. x = 9.
Pennisetum is a large and variable genus, but the bristly, spikelike inflorescence is always readily recognizable. The only other panicoid genus with a similar bristly inflorescence is Setaria, but in that genus the bristles are not deciduous with the spikelets, instead remaining on the rachis at maturity. The bristles are derived from reduced panicle branches.
Many species provide good forage. Several species, including Pennisetum glaucum in China, are used for food.
About 80 species: throughout the tropics; 11 species (four endemic, four introduced) in China.
(Authors: Chen Shouliang (陈守良); Sylvia M. Phillips)