Plants with C4 photosynthesis, annual or
perennial, without noticeable rhizomes, forming tufts or clumps. Flowering
stems erect or ascending, usually branched, sometimes only near the base. Leaf
sheaths open most of their length, the ligule a fringe of short hairs,
sometimes from a minute, membranous base. Leaf blades narrow, often inrolled.
Inflorescences narrow panicles or spikelike racemes (broad panicles with
spreading branches elsewhere). Spikelets with 1 fertile floret, disarticulating
above the glumes. Glumes 2, the lower occasionally shed early, papery, linear
to narrowly lanceolate, with 1, 3, or 5 nerves, often with an awn, in species
with multiple nerves the upper glume also with 2 soft lateral awns. Lemmas
hardened, linear, wrapped around the palea and fruit, rounded on the back, 3‑nerved,
yellowish green or more commonly green mottled with purple, the tip tapered to
3 awns, these sometimes united into a column at the base, the lateral awns
sometimes reduced and much shorter than the central awn. Paleas much shorter
than the lemmas, usually 2‑nerved, lacking awns. Stamens (1)3. Fruits
linear, shed inside the persistent lemmas. About 250 species, worldwide, but
most abundant in tropical and warm‑temperate regions.
Although the long, often bent or twisted awns of Aristida
species aid in dispersal of the fruits in animal fur or botanists’ socks, they
render these grasses relatively uninteresting as forage to livestock and other
grazers, which can receive injuries to the noses, eyes, mouths, and intestines
when attempting to graze on them.