An annual grass, up to 5 feet tall, blooming in summer. Leaves and stalk may be tinged red. Leaves are relatively narrow for a grass, 4 to 20 inches long and 1 to 1.25 inches wide. One of few grass species that do not have a ligule, a membranous or hairy structure between the leaf and the stalk. Inflorescence relatively compact. Spikelets (flowers) large, each developing a long stiff hair (awn) at the end, especially the terminal spikelet. The flowers are greenish to purplish, turning reddish brown.

An invasive exotic plant from tropical Africa and Asia. It can thrive anywhere that is wet to damp, rice paddies, ditches, pond edges, damp roadsides, and low spots in cultivated fields, and is considered one of the world's worst weeds. In North America, it infests Mexico, every US state (except Alaska) and all provinces of Canada (but not the northern territories). In Wildwood it is common along the edge of the entrance wetland and in ditches along Wildwood Drive.

The lack of a ligule is the best identifying character, but for the layperson, the stiff awns on the inflorescence are more useful.