Description from Flora of China
Annuals or perennials. Culms usually branched near the base. Leaf blades usually flat; ligule a ciliate rim. Inflorescence spikelike, cylindrical, composed of spiny or bristly deciduous burrs arranged along an angular, often sinuous rachis; burrs sessile or with an obconical basal stipe, each composed of 1 or more sessile spikelets surrounded by an involucre of spines and bristles; bristles flexuous or more often spinous, ± flattened, grooved on the outer face, united below, the degree of union varying from a small basal disk to a deep cupule, inner spines or bristles often ciliate around spikelets. Spikelets lanceolate, acute; glumes unequal, shorter than spikelet, lower sometimes suppressed; lower floret membranous, staminate or neuter; upper floret firmer, protogynous. Lodicules absent.
Twenty-three species:tropical and warm-temperate regions of the world; four species (all introduced) in China.
(Authors: Chen Shouliang (陈守良); Sylvia M. Phillips)