Annual bluegrass is a highly diverse species with some subspecies functioning as short-lived perennials. The ligule is long and membranous and no auricles are present. Small but conspicuous open-panicle seedheads are evident during most of the growing season.
Most seeds germinate in late summer or early fall.
Although this species can persist throughout the entire growing season on irrigated sites, it usually dies during hot, dry conditions if not irrigated. Barnyardgrass seeds germinate later than crabgrass seeds, and plants do not tolerate low mowing heights. This species has no ligule or auricles. The seedhead is composed of compact spikes arising at several locations on the main stalk. Barnyardgrass can be a problem in newly established turf if seed is introduced with the topsoil.