|Description from A.S.
Hitchcock (1925). Will be enhanced by Barkworth later.
Culms 50-80 cm, erect, glabrous, the whole plant pale green; sheaths mostly glabrous, hispid at the throat, often concealing cleistogamous panicles; ligule a membrane about 1 mm long or less, ciliate with stiff hairs 1-2 mm long; blades folded or involute, or the older lower ones flat, rather firm, glabrous, subulate-pointed, 10-20 cm long, 1-2(4) mm wide. Panicle 10-20 cm long, narrow, pale, rarely purplish, often more or less enclosed in the upper leaf sheath, the branches in widely spaced fascicles, ascending or appressed, naked below, bearing several spikelets about, the rachis internodes glabrous, the lowermost node densely pilose, the other nodes more or less pilose. Glumes equal, about 8 mm long, papery, broad, abruptly acuminate, 3-veined, scaberulous on the veins and somewhat so between the veins; callus about 1 mm long, densely barbed with white hairs; lemma about 6 mm, fusiform, pale, densely white-villous below, glabrate in streaks above, narrowed toward the summit, this ciliate with stiff bristles about 1 mm long; awn 11-18 cm long, twice-geniculate, almost smoother, scaberulous on the angles only, slightly twisted to the second bend, the first and second segments each 3-5 mm long.
Hitchcock notes that Columbian specimens differ in having a nearly glabrous ligule and in the lower nodes of the panicle being scarcely pilose and in being less pilose at the summit of the lemma an in appearing more lax. 'They may be a distinct species". He states that A. brachychaetum differs in having involute blades and somewhat smaller fruits and awns. Unfortunately, he doe snot include A. clandestinum in his key to South American Stipa