Plants annual; tufted. Culms 12-45 cm, erect or decumbent. Ligules 1.5-5.5 mm, obtuse; blades 4-12 cm long, 1.2-4 mm wide; upper sheaths conspicuously inflated. Panicles 1.5-6.5 cm long, 5.5-10 mm wide, often dense. Glumes 3-5 mm, connate at the base, not dilated, membranous, pubescent, keels not winged, ciliate, apices obtuse; lemmas 3-5 mm, connate in the lower 1/3-1/2, glabrous, apices obtuse, awns 6-10 mm, geniculate, exceeding the lemmas by 3-6 mm; anthers 0.7-1.8 mm, yellow to rusty-brown. Caryopses 1.5-2 mm. 2n = unknown.

Alopecurus saccatus is a native annual that inhabits moist, open meadows, valley plains, and vernal pools at elevations below 700 m from Washington to California. Segregates have been treated as species in the past, but the variation between them appears to be continuous, and no habitat differentiation is evident.