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Annuals or perennials. Leaf-blades flat or involute; ligule a line of hairs. Inflorescence a cylindrical spike-like panicle with angular rhachis, each spikelet or cluster of spikelets enclosed by a deciduous involucre; involucre composed of 1 or more whorls of bristles, those of the innermost whorl ± flattened and often spiny, connate at the base or for some distance along their length. Spikelets lanceolate to ovate, dorsally compressed, acute to acuminate; lower glume up to 1/2 as long as the spikelet, sometimes suppressed; upper glume a little shorter than the spikelet; lower floret ♂ or barren, its lemma as long as the spikelet, membranous; upper lemma as long as the spikelet, firmly membranous to coriaceous, the flat thin margins covering much of the palea. Caryopsis elliptic to ovoid, dorsally compressed.
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.
Spikelets sessile, enclosed in spiny burs composed of united sterile branches, the burs falling entire, the body of the bur irregularly lobed, the lobes rigid, the spines barbed; spikelets 1 to several in each bur, usually glabrous; first glume narrow, 1-nerved, much shorter than the spikelet, sometimes wanting; second glume and sterile lemma nearly equal, 3-to 5-nerved, the lemma enclosing a palea and usually a staminate flower; fruit indurate, the lemma acuminate, the margins thin, flat.
Inflorescence a cylindrical spiciform panicle with angular rhachis, bearing deciduous clusters of 1-several spikelets subtended by an involucre of bristles, these flexuous or spinous, ± flattened and united below (at least the inner whorl), the degree of union varying from a basal disk to a deep cupule.
Superior glume and inferior lemma as long as spikelet or a little shorter.
Superior lemma chartaceous to thinly coriaceous with flat thin margins.
Inferior glume up to 1/2 length of spikelet, sometimes suppressed.
Spikelets lanceolate to ovate.
Pending.
