Plants annual; tufted. Culms 2-30 cm, bases often prostrate or decumbent, strongly branching. Sheaths glabrous or sparsely hirsute; ligules 0.7-1.5 mm, lacerate; blades 1-7 cm long, 1-2 mm wide, glabrous or puberulent. Panicles 2-6 cm. Lateral spikelets 1.5-2.3 mm, on 1-1.3 mm pedicels; central spikelets 2.5-3.2 mm, on 0.3-0.6 mm pedicels. Glumes 1.3-1.8 mm, flabellate, lobes rounded, awns 0.1-0.6 mm; lemmas 2.5-3.2 mm, central awns 3-8 mm, lateral awns to 1 mm; anthers 0.5-0.8 mm. 2n = 20, 60.
Aegopogon tenellus usually grows between 1550-2150 m in shady habitats of moist canyons, but it is sometimes found along roadsides and in other open areas. Its range extends from southern Arizona into northern South America. In some plants, the lateral spikelets are reduced (Aegopogon tenellus var. abortivus (E. Fourn.) Beetle), but such spikelets (and central spikelets with reduced awns) are also found in plants with normal spikelets, so taxonomic recognition is not warranted.