Annual or perennial herbs, rarely shrubs or trees, sometimes with rhizomes or stolons; stems erect, ascending or creeping, usually branched at the base, in perennials with sterile shoots and flowering stems (culms) mixed, in annuals only the latter present; culms cylindrical, rarely flattened, jointed, usually hollow in the internodes, closed at the nodes; branches subtended by a leaf, and with a 2-keeled hyaline leaflet (prophyll) at the base. Leaves solitary at the nodes, sometimes crowded at the base of the stem, alternate and 2-rowed, consisting of sheath, ligule and blade; sheaths encircling the stem, with the margins free and overlapping or ± connate, frequently swollen at the base, the shoulders sometimes extended upwards into triangular auricles; ligule adaxial, placed at the junction of sheath and blade, membranous or reduced to a fringe of hairs, rarely absent (very rarely with a similar abaxial structure, the external ligule); blades usually long and narrow, rarely broad, flat or sometimes rolled or terete, parallel-nerved, rarely with transverse connections, usually passing gradually into the sheath, sometimes amplexicaul or with falcate auricles, rarely narrowed into a false petiole or articulated with the sheath. Inflorescences made up of spikelets arranged in a panicle, or in spikes or racemes, these either solitary, digitate or disposed along a central axis, usually terminal, sometimes (especially in Andropogoneae) numerous, each inflorescence being subtended by a bladeless sheath (spatheole) and the whole flowering branch system condensed into a leafy false panicle. Spikelets consisting of bracts distichously arranged along a slender axis (rhachilla); the 2 lower bracts (glumes) empty; the succeeding 1 to many bracts (lemmas) each enclosing a flower and opposed by a hyaline scale (palea), the whole (lemma, palea and flower) termed a floret; base of spikelet or floret sometimes with a horny prolongation downwards (callus); glumes or lemmas often bearing 1 or more stiff bristles (awns); this basic pattern of spikelet structure consistent throughout the family, though often much modified by reduction, suppression or elaboration of parts. Flowers usually bisexual, sometimes unisexual, small and inconspicuous; perianth represented by 2, rarely 3, minute hyaline or fleshy scales (lodicules); stamens hypogynous, 1-6, rarely more, usually 3, with delicate filaments and 2-thecous anthers opening by a longitudinal slit or rarely a terminal pore; ovary 1-locular, with 1 anatropous ovule often adnate to the adaxial side of the carpel; styles usually 2, rarely 1 or 3, generally with plumose stigmas. Fruit mostly a caryopsis with thin pericarp adnate to the seed, rarely with a free seed, still more rarely, a nut or berry; caryopsis commonly combined with various parts of the spikelet, or less often the inflorescence, to form a false fruit; seed with starchy endosperm, an embryo at the base of the abaxial face, and a point or line (hilum) on the base of adaxial face marking the connection between pericarp and seed.