Habit: annual to perennial; herbaceous or woody (bamboos); prostrate and matforming to erect, sometimes bushy or treelike bamboos. 

Stems usually annual,  or, in bamboos, perennial, round of oval in ceoss-section, never triangular, not even below the inflorescences. 

Leaves: Alternate, in 2-ranks, with sheathing bases and linear blades that are usually separated from the sheath on the upper (inner) side by a ligule of skinlike tissue or a line of hairs, usually all leaves similar but bamboos have 2 sets of leaves, those on the vertical stems, the culm leaves, often with deciduous blades that are not or only a few times wider than long, those on the branches, the foliage leaves, with persistent blades that are longer in proportion to their width and often narrow at the base to a petiole-like structure, the pseudopetiole. 

Inflorescences: compound, the evident structures, synflorescences, composed of 1-many primary inflorescences, in diverse arrangements from a single terminal spikelets to terminal or axillary paniculate or spikelike clusters of spikelets; spikelets, composed of 1-many inconspicuous florets subtended by subtended by 2 (sometimes 1) bracts, the glumes; florets composed of individual flowers enclosed by 2 bracts, the lemma and palea, alternate and distichous on the spikelet stem, the rachilla. 

Flowers: bisexual or unisexual, sometimes varying within a spikelet; perianth absent of composed of 2-3 ldicules, these inconspicuous structures that swell at anthesis and then collapse; stamens usually 1-3, varying to 6 or many; gynoecia with 1 compound pistil, usually with 2-3 style branches, these usually plumose.

Size and importance: Poaceae, with around 12,000 species, is the fourth largest family of flowering plants in terms of number of species but by far the most widespread, growing in almost all terrestrial habitats, often as the dominant component of the vegetation. The importance of grasses is reflected in the number of languages that have a term for describing areas dominated by grasses. Both grasslands and individual grass species have been, and continue to be, of major importance in many parts of the world.

Additional comments: Identifying a plant as a grass is not difficult. Some resemble members of the Cyperaceae, but differ in having 2-ranked leaves, stems that are round or oval in cross-section even beneath the inflorescence, and having 2, not 1 bract, enclosing their flowers. Identifying grass genera and species is more difficult, chiefly because the structures are unfamiliar and differences among them frequently require use of a hand lens.  

T.A. Cope (1995) Poaceae (Gramineae). Flora of Somalia 4: 148-270

Plants annual or perennial herbs (in other parts of the world, sometimes woody trees or shrubs), sometimes rhizomatous or stoloniferous. Stems cylindrical, jointed; internodes usually hollow; branches subtended by a leaf and with an axillary a 2-keeled hyaline leaflet, a prophyll. Leaves soliary, sometimes concentrated at the base of the stems, alternate and 2-ranked, comprising a sheath, ligule, and blade; sheaths encircling the stems, the margins free and overlapping or partially to almost completely connate, aometimes extended at the top into triangular auricles; ligules adaxial, at the sheath-blade junction, membranous or a fringe of hairs, rarely absent; blades usually long and narrow, usually flat, conduplicate, or convolute, rarely terete, usually passing graduually into the sheaths, sometimes amplexicaul, rarely narrowed into a false petiole or articulated with the sheaths. Inflorescences compound, terminal, or terminal and axillary, composed of 1-many primary inflorescences, the spikelets, these usually aggregated into somple panicles, panicles composed of spikelike branches, spikes, or racemes, axillary branches sometimes complex and subtended by bladeless sheaths, spatheoles, very occasionally inflorescences of only one spikelet. Spikelets composed bracts distichously arranged on a central axis, the rachilla, the lowest (1-)2 bracts (the glumes) empty. subsequent bracts, termed lemmas, with an opposing, usually 2-keeled, bract,  the lemma and palea concealing the floral organs between them; flowers uusually bisexual, small and inconspicuous; perianth composed of 2(-3) minute, hyaline scales, the lodicules; stamens 1-6, usually 3, rarely more, hypogynous,; ovaries 1-locular, with 1 ovule, often adnate to the inside of the ovary wall; styles usually 2(-3), stigmas usually plumose. Fruits uually caryopses, the seed wall being adnate to the inside of the ovary wall, occasionally the two not adnate and the fruits nuts of drupes; seeds with lots of starchy endosperm.

The Poaceae family has about 770 genera and 12,000 spcecies. It is global in its distribution, being present in almost every terrestrial habitant and dominant or subdominant in many of them. It is only the fourth largest plant ffamily in terms of species number, but it clearly the most conomically important family, providing food for humans and their livestock. In addition, its woodymembers, primarily the bamboos, are used for construction, furniture, and making cloth.   

Identifying grasses is often considered difficult but much of the difficulty lies in becoming familiar with the structures involved and the many ways in which they are modified, The other problem is that the critical features are often small. 

There has been almost no disagreement as to which species are grasses; there has been less agreement on the delimitation of taxa within the family, particularly at the generic level and below. In this the family is no different from other major plant families. Indeed, it is better than most because their economic importance has led to grasses having been the focus of attention of many taxonomists iover the years. 

Global distribution of the Poaceae.

Several of these records are probably of cultivated plants or escapes from cultivation.