Poaceae - Grass family

Annual or perennial herbs, rarely woody, often with rhizomes or stolons. Culms usually cylindric, usually hollow but solid at the nodes. Leaves: alternate, 2-ranked, simple, consisting of sheath, ligule and lamina; sheath surrounding the stem, usually open; ligule usually present at junction of sheath and lamina, membranous, a row of hairs or 0; lamina linear to filiform, rarely lanceolate or ovate. Inflorescence consisting of numerous spikelets arranged in a spike, raceme or panicle.

The basic unit of the inflorescence is the spikelet, consisting of a number of florets arranged distichously along an axis (rhachilla). At the base of the spikelet are 2 (rarely 0, 1 or more than 2) empty bracts (glumes). Each floret is enclosed within an outer bract (lemma) and an inner bracteole (palea). The palea is usually membranous and 2-keeled, the lemma is usually tougher and often awned. The lemma, palea and flowering parts are together called the floret.

Flowers usually bisexual, but sometimes unisexual. Perianth represented by 2(–3) minute hyaline fleshy scales (lodicules). The base of the spikelet or floret may have a horny prolongation downwards (callus). Stamens (1–)3(–6); anthers versatile. Ovary superior, 1-locular with 1 ovule often attached to the adaxial side of the loculus, to a point or line visible in fruit as the hilum. Styles (1–)2(–3), generally with plumose stigmas. Fruit 1-seeded, usually a caryopsis, rarely with seed free from the pericarp.

Worldwide: 668 genera and 9,500 species, cosmopolitan, but especially tropical and northern temperate sub-arid areas.

Britain: 164 genera and 777 taxa.