Plants perennial; cespitose, not rhizomatous. Culms 40-80 cm tall, 1.5-2.5 mm thick, erect, internodes glabrous; nodes 2-3, pubescent. Sheaths glabrous; collars mostly glabrous, with tufts of hair at the sides, hairs 0.5-1 mm; ligules 0.1-0.3 mm, glabrous, truncate; blades 12-25 cm long, 1.5-2.5 mm wide, flat to convolute, pubescent. Panicles 10-20 cm, open; branches 1-3 cm, ascending to somewhat spreading, scabridulous, with 1-8 spikelets; pedicels 1-8 mm, pubescent. Glumes subequal, 10-15 mm long, 1.5-2 mm wide, narrowly lanceolate, 3-veined, keeled, keels scabrous; florets 6-8 mm long, 0.9-1.1 mm wide, terete, widest near or slightly above midlength; calluses 1.5-2.5 mm, sharp, strigose; lemmas papillose-tuberculate, constricted and purplish below the crown, midveins and exposed marginal veins pubescent over the proximal 2/3, glabrous between the veins at maturity; crowns about 1 mm long, about 0.5 mm wide, conspicuous, more or less straight-sided, purple, rims with 1-1.5 mm hairs; awns 30-50 mm, clearly twice-geniculate, terminal segment straight; anthers 3-4 mm in putatively chasmogamous florets, 0.3-0.5 mm in cleistogamous florets, both ranges sometimes present within a panicle. Caryopses about 3 mm. 2n = unknown.
Nassella manicata is native to Ecuador, Chile, Argentina, and Uruguay, growing on the foothills of the Andes Mountains. It is established in three California counties, growing in disturbed sites, including grazed meadows and old gold tailings. It has also been recorded from Mississippi; it is not known whether the Mississippi population has persisted.
Nassella manicata resembles N. leucotricha and N. pulchra. It differs from both in its shorter florets and more strongly developed crowns. It was misidentified as Nassella formicarum (Delile) Barkworth in the Jepson Manual (Barkworth 1993).