Perennials, loosely tufted or with isolated shoots, strongly rhizomatous, often forming turf; shoots extra- and often intravaginal. Plants green to pale or yellowish green, or purplish to strongly grayish glaucous. Culms 10–120 cm, 1–2.5 mm in diam., erect or decumbent, 1 to several per tuft, smooth, nodes (1–)2–4, 1 or 2 exserted. Leaf sheaths moderately compressed and keeled, uppermost closed for (1/4–)1/3–2/5 of length, smooth or infrequently retrorsely scabrid or pilulose; blades flat or folded, papery to thickly papery, 1–5 mm wide, surfaces smooth or sparsely scabrid, margins scabrid, adaxially glabrous or frequently sparsely hispidulous to strigulose, of tillers, flat or folded with margins inrolled, intravaginal ones when present often folded, 0.5–2 mm wide, extravaginal ones flat or folded (1–)1.5–5 mm wide; ligule whitish, 0.5–4(–5) mm, abaxially nearly smooth to densely scabrid, apex truncate to rounded, often finely scabrid to ciliolate or pilulose. Panicle loosely contracted to open, oblong to broadly pyramidal, erect or slightly lax, (2–)5–20(–25) cm, longest internodes 1–4.2 cm; branches steeply ascending to widely spreading, (2–)3–5(–9) per node, rounded or distally angled, nearly smooth to distally scabrid with hooks on and between angles, longest branch 1.5–5(–10) cm with (3–)7–18 spikelets in distal 1/3–2/3, sometimes clustered distally. Spikelets ovate, green or grayish, frequently purple tinged, 3–7(–9) mm, florets 2–5(–9); vivipary absent in China; rachilla internodes 0.5–1(–1.2) mm, smooth, glabrous (rarely sparsely pilulose); glumes subequal, strongly keeled, keels and sometimes lateral veins dorsally scabrid, first glume 1.5–3(–4) mm. 1–3-veined, upper glume 2–4 mm, 3(or 5)-veined; lemmas ovate to lanceolate (or narrowly lanceolate), 2.5–4(–5) mm, apex slightly obtuse to acuminate, keel villous for 3/4 of length, marginal veins to 1/2 length, intermediate veins prominent, glabrous (rarely sparsely pilulose), glabrous between veins, minutely bumpy, sparsely scabrid distally; callus webbed, hairs as long as lemma, frequently with less well-developed tufts from below marginal veins; palea usually narrow, glabrous or with sparse hooks, usually minutely bumpy, glabrous between keels, keels scabrid, infrequently medially pilulose in subsp. pruinosa. Anthers (1.2–)1.4–2.5(–2.8) mm, infrequently poorly formed, but not vestigial. Fl. and fr. Jun–Sep. 2n = 28–144.
5. Poa pratensis L., Sp. Pl. 67 (1753). Tipo: Europa. N.v.: Pasto azul.
Perennes rizomatosas. Tallos 10-110 cm, erectos. Hojas glabras; lígula 0.2-3 mm; láminas 10-30 cm x 2-3 mm, las láminas basales blandas, patentes. Panícula 3-14 cm, piramidal, abierta; ramas 3-6 en el nudo más inferior, patentes, desnudas en el 1/2-2/3 inferior. Espiguillas 4-6.5 mm, adpresas; gluma inferior 2-3 mm, 1-3-nervia; gluma superior 2.6-3.7 mm, 3-nervia; flósculos 2-5; lemas 3-4 mm, la quilla y las nervaduras marginales pelosas, el callo lanoso; páleas escabriúsculas en las quillas. Potreros húmedos. CR (Pohl y Davidse 11713, ISC). 2600-3100 m. (Cosmopolita en climas templados y húmedos en el hemisferio norte; introducida de Europa.)
Esta especie es ampliamente usada como pasto forrajero en potreros. Ha sido, probablemente, más ampliamente introducida en Mesoamérica, de lo que los escasos ejemplares de herbario procedentes de Costa Rica nos muestran.
Plantas hasta ca. 70 cm, rizomatosas, los tallos erectos. Hojas con lígula hasta ca. 3 mm; lámina 9–25(–32)cm × 2–3 mm. Infl. 3.5–12 cm, abierta, verde púrpura a verde, las ramas patentes. Espiguillas 4–6 mm;glumas 1–3-nervadas, la superior 2.5–3.5 mm; lemas 3–4 mm, la quilla y las nervaduras pubescentes, el callolanoso.
"Rhizomatous, forming a dense sod, or in tufts on long rhizomes in open ground; culms 3–10 dm; sheaths usually glabrous; blades soft, 2–5 mm wide, seldom narrower and involute; ligule shorter than wide; infl ovoid, fairly dense, with spreading or ascending branches, the lower mostly in sets of 5 or 4; spikelets 3–5-fld, with very short rachilla-joints; first glume 1.8–2.9 mm, the second 2.3–3 mm; lemmas distinctly 5-veined, thinly to densely hairy on the veins below but glabrous between them, webbed at base, the lowest 2.5–3.5 mm; anthers 1–1.4 mm; 2n=21–147. Moist or dry soil, avoiding acid soils and heavy shade, throughout the U.S. and far n., often cult. in lawns and meadows; in most of our range intr. from Europe, but probably native along our n. boundary and in Can. (P. angustifolia; P. subcaerulea) Some nematode-infested plants in the ne. part of our range have notably larger, 7-veined lemmas and often a reduced and stiff infl."
Perennial, loosely to compactly tufted or rhizomatous (rhizome long and wiry), up to 0.6 m high. Leaf blades 60-250 mm long, 2-5 mm wide; ligules truncate, up to 2 mm long. Spikelets 3.0-5.5 mm long. Panicle ovate, 50-200 mm long, lowest branches whorled; spikelets 2-5-flowered, aggregated on upper part of branches; lemma keel and marginal veins pilose; anthers 1.5-2.0 mm long.
Like P. binata but lowest panicle branches whorled, basal sheaths not fibrous and lemmas woolly below.
Perennial; up to 0.6 m high; loosely to compactly tufted or with long rhizome; stout and wiry or absent. Leaf blades 60-250 x 2-5 mm; upper ligules truncate; rounded to obtuse; up to 2(3) mm long; basal sheaths usually not fibrous. Flowers: panicle open; ovate; 50-200 mm long; lowest branches whorled; spikelets 3.0-5.5 mm long; spikelets 2-5-flowered; aggregated on upper part of branches; keels and margins densely hairy to middle; base with long fine woolly hairs; anthers 1.5-2.0 mm long.
Mesic Grassland. Moist shady areas; usually in mountains.