Plants annual or perennial; usually cespitose. Culms annual, erect, solid or hollow, usually unbranched. Leaves distichous; sheaths usually open; auricles absent; abaxial ligules absent or of hairs; adaxial ligules membranous and ciliate or of hairs; blades without pseudopetioles; mesophyll cells radiate or non-radiate; adaxial palisade layer absent; fusoid cells absent; arm cells absent; kranz anatomy absent or present, when present, with 1 or 2 parenchyma sheaths; midribs simple; adaxial bulliform cells present; stomatal subsidiary cells dome-shaped or triangular; bicellular microhairs present, with long, slender, thin-walled terminal cells. Inflorescences terminal, not leafy, usually panicles, sometimes spikes or racemes. Spikelets bisexual, with 1 floret; rachilla extension absent; disarticulation above the glumes. Glumes 2, usually longer than the florets, usually acute or acuminate; florets terete or laterally compressed, with well-developed calluses; lemmas 1- or 3-veined, more or less coriaceous, with a germination flap, lemma margins overlapping at maturity and concealing the paleas, apices evidently 3-awned; awn bases often forming a column, lateral awns occasionally reduced or absent; paleas less than 1/2 as long as the lemmas; lodicules usually present, 2, free, membranous, glabrous, heavily vascularized; anthers 1-3; ovaries glabrous; haustorial synergids absent; styles 2, free to the base but close. Caryopses usually fusiform, falling with the lemma and palea attached; hila short or long, linear; endosperm hard, without lipid; starch grains compound; embryos small or large relative to the caryopses; epiblasts absent; scutellar cleft present or absent; mesocotyl internode elongated; embryonic leaf margins meeting. x = 11, 12.

The subfamily Aristidoideae includes only one tribe, the Aristideae. Other taxonomists have generally included the Aristidoideae, with the Danthonieae and Arundineae, in the Arundinoideae (e.g., Watson et al. 1985; Clayton and Renvoize 1986; Kellogg and Campbell 1987), but Esen and Hilu (1991) demonstrated that Aristida is clearly distinct from the Danthonieae and Arundineae in terms of its prolamins. Subsequent work has provided further support for themonophyly of the three tribes, but their position relative to each other and other members of the PACCAD clade is more equivocal.