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Genus Poa Family Poaceae

Description: Tufted annuals or perennials often forming large tussocks, sometimes rhizomatous or stoloniferous.

Culms erect or prostrate, slender, unbranched or branched, especially near the base, if so vertical or oblique rhizomes may be formed. Ligule membranous, to 10 mm long or reduced to a short rim with hairs; blade folded in bud, flat, involute or folded, often narrow or bristle-like, tip often blunt and keeled.

Inflorescence an open or contracted panicle. Spikelets solitary, 3–12 mm long, pedicellate, laterally compressed, rachilla disarticulating above the glumes and between the lemmas, 2–several-flowered, the uppermost florets reduced. Glumes acute, keeled, unequal, the lower 1-nerved, the upper 3-nerved, usually shorter than adjacent lemmas. Lemmas keeled, acute, rarely obtuse, 5-nerved, ± hairy on the back towards the base, awnless, callus short often with loose, woolly hairs (‘web’); palea slightly shorter than the lemmas, scabrous or ciliate on the two keels.


Distribution and occurrence: World: A large genus of >200 spp., in temperate and cold climates and extending into the upland tropics. Australia: c. 40 species (c. 34 species native, 6 species naturalized), all States.

Key after Vickery (1970). P. pratensis is planted as a pasture and lawn species; many species are major components of montane and alpine grasslands; a few species are regarded as weeds.

Text by Jacobs, S.W.L., Whalley, R.D.B. & Wheeler, D.J.B.
Taxon concept: Grasses of New South Wales, Fourth Edition (2008).

 Key to the species 
1Robust perennials growing on coastal foredunes; leaves erect, stiff; inflorescences rarely exserted above leaves; lemmas glabrous (in NSW), apiculatePoa billardierei
Annuals or perennials but not growing on coastal foredunes; if leaves stiff and erect then alpine or subalpine species; inflorescences usually exserted beyond leaves; lemmas never apiculate and hairy or glabrous2
2Small annuals with soft leaves, 2–30 cm tall; ligule soft and thin, glabrous; web on lemma absent3
Perennials rarely < 10 cm tall unless grazed or mown; ligule soft or firm, glabrous or hairy; with or without web on lemma
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5
3Panicle narrow with erect spikelets appressed to the branches; lemmas 3.5–4.5 mm longPoa fax
Panicle triangular to ovate with slender, spreading branches; spikelets spreading at maturity; lemmas 2–4 mm long
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4
4Anthers 0.2–0.5 mm long; lemmas 2–2.5 mm long, separatePoa infirma
Anthers 0.7–1.3 mm long; lemmas 2.5–4 mm long, overlapping
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Poa annua
5Plants with pear-shaped bulbs due to enlargement of the inner leaf sheaths at the base of the plant; web on lemma copiousPoa bulbosa
Plants not bulbous or thickened at the base; with or without web on lemmas
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6
6Internodes of the culm compressed and 2-sided; leaves folded; lemmas 2–3 mm longPoa compressa
Internodes of the culm round or only slightly compressed, rarely strongly compressed (in P. fordeana culms may be strongly compressed, the latter has flat leaves and lemma 3.5–5 mm long)
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7
7Spikelets plump; lemmas broadly ovate; palea ovate; keels densely ciliate with hairs in several rows; panicle narrow with rather few spikeletsPoa saxicola
Spikelets laterally compressed; lemmas not broadly ovate; paleas ± ciliate on keels but hairs in one row only; panicle ± narrow, but if narrow then numerous spikelets
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8
8Leaf-blades smooth or scabrous on the abaxial surface but not obviously hairy; lemmas pubescent over the lower back or hairy on the nerves and keel only9
Leaf-blades hairy on abaxial surface, the leaf-sheath often hairy; lemmas usually pubescent over the lower back (nerves, keel and internerves)
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32
9Ligule a thin, almost translucent membrane, not scabrous and without obvious hairs on the back, nor ciliate, 2 mm long or more (rarely less)10
Ligule a firm (not translucent) membrane, scabrous or puberulous on the back and/or ciliate at the apex or reduced to a rim of hairs, 0.1–2 mm long (-3 in P. costiniana)
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14
10Tufted perennnials without rhizomes or stolons; leaf-blades 4–15 mm wide, broad and flat; lemma nerves raised above the surface; tall plant of rainforest margins with culms to 1.5 m tallPoa queenslandica
Tufted perennials also producing stolons or rhizomes; leaf-blades narrower, not >6 mm wide; lemma nerves ± prominent; plants usually not as tall as previous species
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11
11Plants with leafy stolons; ligule acute to acuminate, 4–10 mm long12
Plants not stoloniferous but with rhizomes; ligule obtuse to truncate and not usually >5 mm long
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13
12Loosely tufted perennials with extravaginal innovations and creeping leafy stolon; blades flat or folded, finely scabrous to subsmooth; ligule 4–10 mm long; lemma rather distictly dorsally curvedPoa trivialis
Caespitose perennials with mostly intravaginal innovations; blades inrolled, capillary, loosely hispid to scabrous; ligule 1–4.5 mm long; lemma not distinctly dorsally curved
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Poa hookeri
13Spikelets 8–10 mm long and strongly compressed; peduncle compressed and branches widely spreading at maturity; lemmas woolly hairy over lower back; leaf-sheaths of lower leaves closed at the basePoa fordeana
Spikelets 2.5–6 mm long and not as strongly compressed; lemmas hairy on the keel and marginal nerves and not between (the internerves); web prominent; leaf sheaths open
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Poa pratensis
14Leaf-blades broad or narrow, flat or folded and V-shaped in cross-section, the edges sometimes inrolled on drying15
Leaf-blades (excluding flag-leaf) narrow, closely folded or tightly rolled so that the leaves are bristle-like or angular to round in cross-section
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22
15Stems often leafy, branching from aerial nodes to form leafy shoots; plants tufted and/or stoloniferous16
Leaves mostly basal and culms usually unbranched; plants tufted or rhizomatous
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17
16Leaf-blades firm to rigid, 1–5 mm wide when opened out; plants robust and erect (stems to 1.2 m tall); ligule often ciliolate; panicle often rather contracted with many spikelets; lemmas pubescent on lower back with longer hairs on nerves and keelPoa affinis
Leaf-blades much softer, 1–1.5 mm wide when opened out, almost thread-like in some plants; tufted and stoloniferous plants; ligule not ciliolate; panicle open with few spikelets on long, slender branches; lemma pubescent on the lower back (including nerves) to glabrous
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Poa tenera
17Plants usually with horizontal rhizomes that produce new shoots outside the limits of the parent tussock18
Plants tufted, not producing rhizomes outside the parent tussock (rhizomes may develop in a vertical or oblique direction in response to environmental changes)
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20
18Lower leaf-sheaths usually with a purplish colouration; lemmas usually pubescent on the internerves, nerves and keel; leaf-blades rigidPoa ensiformis
Lower leaf-sheaths not purplish, lemmas glabrous on the internerves but hairy on the nerves and keel; leaf-blades ± rigid
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19
19Leaf-blades rigid; rhizomes short, thick, with firm, obtuse scales; spikelets strongly compressedPoa cheelii
Leaf-blades soft to moderately firm, rhizomes slender with firm, pointed scales; spikelets not strongly compressed
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Poa pratensis
20Panicle usually contracted, ± linear, if with spreading branches then at least some of them short and with spikelets almost to their bases; spikelets usually large (lemmas 3–6 mm long); leaf-blades smooth on the abaxial surface; plant of coastal foreshores and estuariesPoa poiformis
Panicle spreading at maturity and branches bare of spikelets in the lower part; spikelets smaller, 2.5–4 mm long; leaf-blades scabrous on abaxial surface; not usually on coastal foreshores
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21
21Leaf-blades 1–3.5 mm wide, a dull green or greyish-green in colour; peduncle usually round in cross-section; the common large tussock grass of moist areas below 1500 m altutudePoa labillardierei
Leaf-blades 3–8 mm wide, usually light-green in colour when alive, peduncle usually compressed, tussock grass of wet areas of elevations c. 1300 metres
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Poa helmsii
22Culms branched with aerial shoots or plants stoloniferous and/or trailing; leaves fine and soft, c. 0.5 mm or less in diameter23
Tussocks rarely producing aerial shoots and without stolons; leaves variable in width and texture
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24
23Tussocks lax; web on lemma often absent; lemmas pubescent or glabrous on lower back; leaves not usually bluish in colourPoa tenera
Tussocks more erect; web usually present, lemmas pubescent on lower back; leaves usually bluish
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Poa sieberiana
24Panicle contracted and often linear, if with spreading branches then some short, with spikelets almost to their bases; lemmas relatively large, usually 4–5 mm long; grows on coastal foreshoresPoa poiformis
Panicle spreading at maturity, if contracted then the lower branches bare at their bases; lemma length variable; not usually on coastal foreshores
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25
25Hairs on the lower back of lemmas concentrated along the keel and lateral nerves, the internerves usually glabrous but a few scattered hairs may be present; palea scabrous towards the apex, not usually ciliolate26
Lower back of lemmas hairy all over, pubescent on the internerves and often with longer and/or denser hairs on the keel and lateral nerves; palea scabrous above and usually ciliolate below
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29
26Leaf-blades smooth on outer surface and rigid; tussocks not usually large and grows in wet places of alpine and subalpine regionsPoa costiniana
Leaf-blades very lightly to distinctly scabrous on the outer surface and not particularly rigid; habitat variable
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27
27Robust grass, forming large tussocks with leaves 0.5 mm or more in diam. Common in wet placesPoa labillardierei
Plants less robust, forming small tussocks with fine leaves <0.5 mm diam.; not very common
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28
28Glumes narrow and lemmas small, the latter 2–3.5 mm long; leaves relatively softPoa meionectes
Glumes broader and lemmas longer, the latter 3–4 mm long; leaves more rigid
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Poa clivicola
29Leaf-blades smooth to touch on outer surface30
Leaf-blades moderately to distinctly scabrous or smooth on outer surface, if smooth then leaves dull green and lemmas small, 1.8–3 mm long
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31
30Leaf-blades soft and bright green when alive; lemmas 2.3–5 mm longPoa hiemata
Leaf-blades rigid, often bluish-green; leaf-sheaths usually purplish at the base; lemmas 3–3.5 mm long
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Poa fawcettiae
31Leaf-blades bluish in colour, rigid, with purplish leaf-sheaths; spikelets often purplish; lemmas 2.5–3.5 mm longPoa phillipsiana
Leaf-blades ± bluish, less rigid, bases of leaf-sheaths and spikelets not usually purplish; lemmas 1.8–3 mm long
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Poa sieberiana
32Lemmas 3–4 mm long; leaf-blades with dense, soft, short hairs of equal length; leaf-sheaths purplish at basePoa petrophila
Lemmas usually <3 mm long; leaves with sparse, stiff hairs, or hairs of unequal length; leaf-sheaths not purplish
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33
33Leaves narrow with sparse, stiff hairs, extravaginal shoots often presentPoa sieberiana
Leaves not as narrow, densely hairy with hairs of two lengths, or surface distinctly scabrous between rows of hairs; extravaginal shoots absent
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Poa induta

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