Description taken from Caro and Sanchex 1971
Plants perennial, cespitose. Culms 40-90 cm tall, erect, with cleistoges in the axils of the basal innovation leaves. Leaf sheaths open to the base; ligule 0.25-0.5 mm long, papery, the back pubescent with hairs 0.5-1.5 mm long; blades 8-35 cm long, 2-3 mm wide, convolute-filiform of flat, stiff, straight, glabrous or the margins ciliate, the lower surface smooth or scabrous towards the top, the upper surface surface slightly scabrous, the top somewhat sharp. Panicle 10-25 cm long, lax, with few to many spikelets, sometimes partially included in the upper leaf sheath. Glumes 6-8 mm long, lanceolate-acuminate, the midvein extending into a thin, awnlike tip; first glume 1-3-veined, about 0.5 mm wider than the second and either subequal or a little shorter in length, scabrous over the midvein; second glume 3-veined, the lateral veins much shorter than the midvein and anastamosing with it. Anthecium 4-5.5 mm long; callus 0.4-0.5 mm long, obconic, blunt, with straight white hairs; lemma fusiform, laterally compressed, 5-veined, pubescent throughout or the margins sometimes almost glabrous (varying in this respect within a panicle), the tip narrow and with a ring of hairs 0.5-1.5 mm long, but without a crown; awn 1-1.8 cm long, centric, capillary, persistent, usually twice geniculate, the first segment 2-4 mm, the second segment 2.5-3.5 mm, and the bristle 8-12 mm long; palea slightly shorter than the lemma, coriaceous, opaque, 2-veined, pubescent over and between the veins and with short hairs at the tip, the margins papery and hyaline; lodicules 3, the third slightly less than half as long as the others, membranous, hyaline, without venation; anthers 3, with short hairs on the tips of the anther sacs. Caryopsis 2-3 mm long, about 1 mm in diameter, cylindrical, smooth or with 3 ridges, the style base centric.
Distribution: Argentina (Buenos Aires, Catamarca, Cordoba, Entre Rios, La Pampa, San Fe, Santiago del Estero; France (introduced); Peru (Introduced?); Uruguay. Considered an invasive weed in parts of Argentina.
The inclusion of A. brachychaetum and A.
caudatum in Achnatherum needs to be investigated.