Description from Flora of China
Perennial, stoloniferous; monoecious or dioecious. Leaf blades linear; ligule a line of hairs. Male inflorescence long exserted, racemes 1–4, distant, short; spikelets biseriate, pectinate; rachis slender. Female inflorescence composed of usually 2 modified racemes in axils of inflated upper leaf sheaths; spikelets 3–5; rachis shortened and with the spikelets forming a globular deciduous burr. Male spikelets with 2 florets; glumes unequal, 1-veined; lemmas longer than glumes, 3-veined, entire. Female spikelets dorsally compressed, floret 1; lower (inner) glume reduced or suppressed, thin; upper glume strongly indurated, forming an involucre on the outside of the burr, back rounded, margins inflexed and enclosing floret, apex contracted with 3–5 rigid acuminate lobes; lemma ovate-lanceolate, subleathery, 3-veined, apex shortly 3-lobed. Caryopsis ellipsoid.
One species: native to Mexico and the United States; introduced in China.
(Authors: Sun Bixing (孙必兴 Sun Bi-sin); Sylvia M. Phillips)