Any of about 300 species of grasses in the genus Digitaria, especially D. sanguinalis or the slightly shorter D. ischaemum (smooth crabgrass). D. sanguinalis has long hairs covering its leaves and five or six spikelets; D. ischaemum has no hair and only two or three spikelets. Both are natives of Europe that became widely naturalized as weeds in North America. They and a few closely related species are very troublesome in lawns and fields. One species, Arizona cottontop (D. californica), is a useful forage grass in the American Southwest.