Poa annua L.

Nile region, Oases, Mediterranean region and Sinai.

Cosmopolitan.

Plant / epiphyte
fruitbody of Athelia pyriformis grows on living Poa annua

In Great Britain and/or Ireland:
Foodplant / parasite
Blumeria graminis parasitises live Poa annua

Foodplant / parasite
conidial anamorph of Entyloma irregulare parasitises live leaf of Poa annua

Foodplant / gall
stroma of Epichlo causes gall of stem of Poa annua

Foodplant / pathogen
acervulus of Colletotrichum coelomycetous anamorph of Glomerella graminicola infects and damages root of Poa annua

Foodplant / pathogen
Labyrinthula infects and damages Poa annua

Foodplant / pathogen
strand of Laetisaria fuciformis infects and damages dying plant of Poa annua
Remarks: season: 9-10

Foodplant / saprobe
fruitbody of Marasmius curreyi is saprobic on dead, decayed stem of Poa annua

Foodplant / pathogen
Fusarium anamorph of Monographella nivalis infects and damages leaf sheath (usually close to stem base) of Poa annua
Remarks: season: mainly 10-3
Other: major host/prey

Foodplant / feeds on
adult of Oulema melanopus/rufocyanea agg. feeds on leaf of Poa annua
Remarks: season: 1-12

Foodplant / parasite
hypophyllous, long covered by epidermis telium of Puccinia brachypodii var. poae-nemoralis parasitises live leaf of Poa annua

Foodplant / parasite
uredium of Puccinia graminis f.sp. poae parasitises live stem of Poa annua

Foodplant / parasite
sparse uredium of Puccinia poarum parasitises live leaf of Poa annua

Foodplant / spot causer
Spermospora anamorph of Spermospora poagena causes spots on live leaf of Poa annua

Poa annua is easily distinguished from other short-anthered Poa, other than P. infirma, by the annual habit, absence of a web on the callus, and the near absence of hooks on the panicle branches and spikelet bracts, in combination with densely pubescent palea keels that lack hooked prickle hairs at the apex. Plants with glabrous florets are sporadically encountered.

Plants perennating by short stolons rooting at the nodes appear to develop repeatedly but sporadically at various elevations with prolonged, cool, mesic growing conditions, possibly in response to trampling. These are sometimes placed in var. reptans. Such plants have been recorded from Yunnan.

Annual Meadow-grass is a very common weedy species found in a variety of habitats. 1400-4300m.

Annuals, sometimes over wintering, infrequently stoloniferous. Culms loosely tufted, erect or oblique, often decumbent, often geniculate, soft, 6–30(–45) cm tall, smooth, nodes 1 or 2(or 3), 1(or 2) exserted. Leaf sheath slightly compressed, thin, smooth, uppermost closed for ca. 1/3 of length; blade light to dark green, flat or folded, thin, 2–12 cm × (0.8–)1–3.5 mm, margins slightly scabrid, apex acutely prow-tipped; ligules 0.6–3 mm, abaxially smooth, glabrous, apex obtuse, margin irregularly dentate, smooth. Panicle open, moderately congested, broadly ovoid to pyramidal, (1–)3–10 cm, as long as wide; branches ascending, spreading, or a few reflexed, 1 or 2(–3) per node, smooth, longest with usually 3–5 spikelets in distal 1/2. Spikelets ovate to oblong, dark to light green, (3–)4–5.5 mm, florets 3–5, distal fertile florets often female; vivipary absent; rachilla internodes 0.5–1.5 mm, smooth, glabrous, hidden or exposed; glumes unequal, smooth or rarely keeled with hooks, lower glume lanceolate and acute to subflabellate and obtuse, 1.5–2(–3) mm, 1-veined, upper glume elliptic, 2–3(–4) mm, 3-veined, the margin angled; lemmas ovate, 2.2–3.5 mm, apex and margins broadly membranous, intermediate veins prominent, keel and marginal, and usually intermediate, veins villous in the lower 1/2, rarely glabrous throughout; callus glabrous; palea keels smooth, densely pilulose to short villous. Anthers 0.6–1 mm, usually at least 2 × as long as wide, or vestigial. Fl. Apr–May, fr. Apr–Jul. 2n = 28.

Tufted annual or short-lived perennial; culms 5-30cm high, erect, spreading or prostrate, sometimes with a creeping base rooting from the nodes, slightly compressed. Leaf-blades flat or folded, 1-14cm long, 1–2(–5)mm wide, flaccid, abruptly tapered to a pointed or bluntly hooded tip, often transversely wrinkled, scaberulous on the margins; ligule blunt, 2–5mm long. Panicle ovate or pyramidal, (1–)3–8(–12)cm long, loose or rather dense; branches paired, spreading or de-flexed after anthesis, smooth. Spikelets with 3–5(-10) closely spaced florets, ovate or oblong, 3–10mm long, pale or bright green, reddish or purplish; glume unequal, the lower lanceolate to ovate, 1.5–3mm long, 1–nerved, the upper elliptic or oblong, 2–4mm long, 3–nerved; lemmas semi-elliptic or oblong in side-view, 2.5–4mm long, blunt, glabrous or sparsely to densely ciliate on the keel and nerves, without any wool at the base; palea nearly as long as the lemma, ciliate all along the keels; anthers 0.6–0.8(–1)mm long.

Cosmopolitan.

Distribution: Pakistan (Baluchistan, Punjab, N.W.F.P. & Kashmir); cosmopolitan, but avoiding deserts and hot climates.

Anhui, Fujian, Gansu, Guangdong, Guangxi, Guizhou, Hainan, Hebei, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Jilin, Liaoning, Nei Mongol, Qinghai, Shaanxi, Shandong, Shanxi, Sichuan, Taiwan, Xinjiang, Xizang, Yunnan, Zhejiang [Afghanistan, Bhutan, India, Indonesia, Japan, Kazakhstan, Korea, Kyrgyzstan, Malaysia, Mongolia, Myanmar, Nepal, New Guinea, Pakistan, Russia, Sri Lanka, Tajikistan, Turkmenistan, Uzbekistan, Vietnam; Africa, SW Asia, Australia, Europe, North and South America, Pacific Islands].

2300-3500 m

Fl. & Fr. Per.: throughout most of the year, especially March-September.

Weed of disturbed, often moist and shady ground; near sea level to 4800 m.

Poa annua f. reptans (Haussknecht) T. Koyama; P. annua var. reptans Haussknecht; P. crassinervis Honda.

annua: annual

Erect or decumbent annual (very rarely perennial), 5–30 cm. Leaves: ligule 2–3 mm; lamina 1.5–10 × 0.1–0.5 cm, flat, keeled, often transversely wrinkled. Panicle 1–8 cm, ± triangular; branches usually 2 together, often becoming reflexed after flowering. Spikelets 3–5 mm, 3–5-flowered, lanceolate; lower glume ovate or lanceolate, 1-veined; upper 3-veined; lemma ovate, 5-veined, margin and apex broadly hyaline.

Frequent

Annuals, Terrestrial, not aquatic, Stems nodes swollen or brittle, Stems geniculate, decumbent, or lax, sometimes rooting at nodes, Stems mat or turf forming, Stems caespitose, tufted, or clustered, Stems terete, round in cross section, or polygonal, Stems compressed, flattened, or sulcate, Stems branching above base or distally at nodes, Stem internodes hollow, Stems with inflorescence less than 1 m tall, Stems, culms, or scapes exceeding basal leaves, Leaves mostly basal, below middle of stem, Leaves c onspicuously 2-ranked, distichous, Leaves sheathing at base, Leaf sheath mostly open, or loose, Leaf sheath smooth, glabrous, Leaf sheath or blade keeled, Leaf sheath and blade differentiated, Leaf blades linear, Leaf blades very narrow or filiform, less than 2 mm wide, Leaf blades 2-10 mm wide, Leaf blades mostly flat, Leaf blade margins folded, involute, or conduplicate, Leaf blades mostly glabrous, Leaf blades more or less hairy, Ligule present, Ligule an unfringed eciliate membrane, Inflorescence terminal, Inflorescence an open panicle, openly paniculate, branches spreading, Inflorescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Inflorescence with 2-10 branches, Inflorescence branches more than 10 to numerous, Flowers bisexual, Spikelets pedicellate, Spikelets laterally compressed, Spikelet less than 3 mm wide, Spikelets with 3-7 florets, Spikelets solitary at rachis nodes, Spikelets all alike and fertille, Spikelets bisexual, Spike lets disarticulating above the glumes, glumes persistent, Spikelets disarticulating beneath or between the florets, Rachilla or pedicel glabrous, Glumes present, empty bracts, Glumes 2 clearly present, Glumes equal or subequal, Glumes distinctly unequal, Glumes shorter than adjacent lemma, Glumes keeled or winged, Glumes 3 nerved, Lemmas thin, chartaceous, hyaline, cartilaginous, or membranous, Lemma similar in texture to glumes, Lemma 5-7 nerved, Lemma glabrous, Lemma body or surface hairy, Lemma apex acute or acuminate, Lemma awnless, Lemma margins thin, lying flat, Lemma straight, Palea present, well developed, Palea about equal to lemma, Palea 2 nerved or 2 keeled, Stamens 3, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis, Caryopsis ellipsoid, longitudinally grooved, hilum long-linear.

Poa annua, or annual meadow grass (known in America more commonly as annual bluegrass or simply poa), is a widespread low-growing turfgrass in temperate climates. Notwithstanding the reference to annual plant in its name, perennial bio-types do exist. This grass may have originated as a hybrid between Poa supina and Poa infirma.