Description from Flora of China
Panicum verticillatum Linnaeus, Sp. Pl., ed. 2, 1: 82. 1762; Chaetochloa brevispica Scribner & Merrill; C. vertici-llata (Linnaeus) Scribner; Chamaeraphis italica (Linnaeus) Kuntze var. verticillata (Linnaeus) Kuntze; C. verticillata (Linnaeus) Porter; Panicum asperum Lamarck; Pennisetum verti-cillatum (Linnaeus) R. Brown; Setaria brevispica (Scribner & Merrill) K. Schumann.
Annual. Culms tufted, much branched, ascending, 20–100 cm tall, glabrous. Leaf sheaths thin, glabrous or papillose-pub-erulous, margins ciliolate; leaf blades broadly linear, flaccid, 5–20 × 0.4–1.8 cm, usually glabrous, base subrounded, margins scabrous, apex long acuminate; ligule 0.5–1 mm. Panicle densely spikelike, or lobed with short lateral branches on vigorous specimens, 4–15 cm, spikelets subtended by 1–4 bristles; axis shortly hispidulous; bristles green or brownish, 3–8 mm, retrorsely barbed and often becoming entangled. Spikelets elliptic, 1.8–2.4 mm, green with obvious darker veins, obtuse; lower glume 1/3–1/2 as long as spikelet, obtuse; upper glume boat-shaped, as long as spikelet, 7-veined; lower floret neuter; lower palea much reduced; upper lemma dorsally compressed, finely rugose. Fl. and fr. Jun–Sep. 2n = 18, 36.
This is an easy species to recognize because of its clinging, retrorsely barbed bristles.
Roadsides, open weedy places; 300–1000 m. Nei Mongol, Taiwan, Yunnan [tropical and warm-temperate regions of the Old World; introduced in America].