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Published In: Species Plantarum 1: 67. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 6/2/2011)
Acceptance : Accepted
Project Data     (Last Modified On 6/3/2011)
General/Distribution: A genus of about 200 species; cosmopolitan, but mainly in temperate regions particularly of the northern hemisphere; 29 species occur in Pakistan, 1 of them only in cultivation.
Comment/Acknowledgements: A very difficult genus to name, partly on account of the wide range of variation displayed by the species, and partly because many of them are extremely closely related. Numerous rather cryptic characters (anther length, presence or absence of wool on the callus, pubescence of lemma body and palea keels, scabridity of panicle branches, length of ligule) have, of necessity, to be employed in the key, but the distinctions between several of the species must at sometime be re-examined on a biosystematic basis. The-problematical species will be apparent from the key which itself is still far from being fool-proof. It must be stressed that entire specimens complete with the basal parts are required for accurate determination and any reference to characteristics of the lemma refer always to the lowermost of a spikelet.

Two species allied to Poa pratensis have been reported from Pakistan but the presence of neither can be confirmed.Poa compressa Linn. differs by its strongly compressed stems and leaf-sheaths. In Flora Iranica (p. 35) Bor says of it, “Mountain sides in India and Pakistan, meadows in Europe,” but no material is cited. Poa alpigena (Blytt) Lindm. is very much like Poa pratensis but has a more slender habit, narrower leaves and a characteristically curved base. Furthermore, the paleakeels are ciliate below. The only specimen cited for Pakistan by Bor (Stainton 2957), however, lacks the essential feature of ciliate palea-keels and has therefore been accommodated in Poa pratensis in this Flora.


 

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Annuals or perennials. Leaf-blades usually flat, often with a blunt or hooded tip. Inflorescence an open or contracted panicle. Spikelets 2-several-flowered, laterally compressed; glumes subequal or unequal, 1-3-nerved, keeled, usually glabrous; lemmas deeply concave, keeled on the back, membranous but often with hyaline margins, 5-7-nerved, awnless; callus short, obtuse, often with loose woolly hairs; ovary glabrous, the hilum basal and punctiform.
 

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1 Annual or sometimes perennial, keels of palea with flexuous, curved or crispate hairs along their whole length (or almost so) (2)
+ Perennial or rarely annual; keels of palea scabrid or prickly, if hairy then only in the lower half (5)
2 (1) Lower panicle-branches spreading or deflexed after anthesis; spikelets with crowded florets; anthers 0.6-2mm long, at least twice as long as wide (3)
+ Lower panicle-branches erecto-patent after anthesis; spikelets with rather distant florets; anthers 0.2-0.5 mm long, scarcely longer than wide Poa infirma
3 (2) Spikelets not crowded towards the ends of the panicle-branches; anthers 0.6-0.8 (-1) mm long, 2-3 times as long as wide (4)
+ Spikelets crowded towards the ends of the panicle-branches; anthers usually 1.3-2 mm long, 5-8 times as long as wide Poa supina
4 (3) Lemma without any wool at the base Poa annua
+ Lemma with copious wool at the base Poa nepalensis
5 (1) Stem with a bulbous swelling at the base formed from the hardened remains of old leaf-sheaths (6)
+ Stem not bulbous at the base, but sometimes thickened with the scarious or fibrous (not hardened) remains of old leaf-sheaths (8)
6 (5) Lemma ciliate, or at least thinly hairy, on the keel and marginal nerves (7)
+ Lemma entirely hairless though often scabrid Poa bactriana
7 (6) Lemma with wool at the base, this usually copious; lemmas 2.5-3.5mm long; anthers 1-1.5mm long (or spikelets usually proliferating and these characters not visible) Poa bulbosa
+ Lemma without wool at the base (or sometimes just 1 or 2 strands); lemmas 3.5-5mm long; anthers 1.5-2.5mm long (spikelets rarely proliferating in our area) Poa sinaica
8 (5) Plant not as above; if lemma glabrous then plant not over 40cm high and panicle ovate or pyramidal; native wild specie (9)
+ Robust perennial up to 120 cm high; lemma entirely glabrous; panicle narrow; species only in cultivation Poa ampla
9 (8) Lemma hairy on the surface between the nerves (this may be extremely sparse) or sometimes only shortly asperulous (10)
+ Lemma glabrous on the surface between the nerves although the keel and marginal nerves are usually ciliate below (17)
10 (9) Palea-keels ciliate below, scabrid above (11)
+ Palea-keels scabrid throughout their length. (14)
11 (10) Tufted plants without stolons; culms not rooting from the lower nodes; panicle lax or dense (12)
+ Stoloniferous plant with culms often ascending from a procumbent base which sometimes roots from the lower nodes; panicle loose, 12-25cm long Poa stapfiana
12 (11) Spikelets, when young, elliptic or lanceolate; leaf-blades up to 6cm long and 1.5mm wide; panicle contracted, 0.5-5cm long; culms clothed at the base with the scarious remains of old leaf-sheaths (13)
+ Spikelets, when young, broadly ovate; leaf-blades 4-12cm long, 2-5mm wide; panicle compact or spreading, 3-7cm long; culms clothed at the base with the fibrous remains of old leaf-sheaths Poa alpina
13 (12) Dwarf plants up to 10(-15)cm high; wool present at the base of the lower lemmas; leaf blades up to 2cm long Poa koelzii
+ Taller plants up to 30 cm high; wool absent or extremely sparse; leaf-blades 2-6cm long Poa lahulensis
14 (10) Tufted plants without rhizomes, though sometimes with stolons; panicle lax or effuse, not spike-like; lemmas shortly hairy or with a felty pubescence between the nerves below; palea-keels evenly scabrid or prickly (15)
+ Tufted plants with rhizomes; panicle contracted, spike-like; lemma asperulous all over the back; palea-keels with prickles below and teeth above Poa tibetica
15 (14) Lower glume elliptic or oblong, 1-3-nerved; lemmas acute or obtuse; plant tufted, the culms sometimes decumbent at the base and rooting from the lower nodes, but the plant not other-wise spreading by stolons (16)
+ Lower glume subulate-acuminate in side-view, 1-nerved; lemmas obtuse; plant stoloni¬ferous Poa polycolea
16 (15) Robust grass; lemmas acute, gland-pitted on the back and with short, rather coarse hairs below; spikelets 7-8mm long, the florets eventually widely diverging Poa falconeri
+ Slender grass; lemmas very blunt, scabrid on the back and with either a few short hairs or a felty pubescence between the nerves below; spikelets ovate-elliptic, up to 5.5mm long Poa pagophila
17 (9) Palea-keels ciliate below, scabrid above (18)
+ Palea-keels scabrid ± throughout their length (19)
18 (17) Base of the lemma without any wool Poa sikkimensis
+ Base of the lemma with copious wool Poa stewartiana
19 (17) Plants rhizomatous (20)
+ Plants not rhizomatous (23)
20 (19) Lemmas strongly keeled on the back, acute or narrowly obtuse at the tip, narrowly hyaline at most (21)
+ Lemmas very broad, not strongly keeled on the back, rounded and broadly hyaline at the tip Poa calliopsis
21 (20) Uppermost node in the median third of the culm or above; plant loosely or densely tufted from a slender rhizome (22)
+ Uppermost node in the basal third of the culm; plant densely tufted from a short thick rhizome Poa versicolor subsp. araratica
22 (21) Panicle narrow, few-spiculate, the branches 2-3 at the lower nodes; ligule 1.5-3mm long (if ligule not more than 1 mm see 21. P. nemoralis) Poa sterilis
+ Panicle lanceolate to ovate, with many spikelets, often rather dense, with 3-5 branches at the lower nodes; ligule 1-3mm long (if ligule 3.5-10 mm long see 20. P. trivialis) Poa pratensis
23 (19) Anthers 1.3-2.5mm long (24)
+ Anthers 0.6-0.75 mm long Poa setulosa
24 (23) Ligule pointed or blunt, not more than 3mm long (25)
+ Ligule pointed, 3.5-10 mm long Poa trivialis
25 (24) Ligule very short, scarcely exceeding 1mm in length (26)
+ Ligule longer, 1-3 mm long (27)
26 (25) Anthers 1.3-2mm long; lower glume 3-nerved; panicle-branches scaberulous, 2-5 at the lower nodes Poa nemoralis
+ Anthers 1.8-2.5 mm long; lower glume 1-nerved; panicle-branches smooth, paired at the lower nodes Poa aitchisonii
27 (25) Smaller plants, but sometimes reaching 40cm in height; spikelets often becoming wedge-shaped; panicle not ample, either short (2-10cm long) and dense or longer (7-15cm long) but with relatively few spikelets (28)
+ Tall plant, usually 40-120cm high; spikelets ovate or oblong, not becoming wedge-shaped; panicle ample, 10-20(-30)cm long, with branches in distant clusters of 3-6 at a node Poa palustris
28 (27) Plant tufted, not stoloniferous, the culms usually erect; panicle narrow, lax or dense (29)
+ Plant stoloniferous, the culms erect or geniculately ascending from a creeping base; panicle very loose and spreading Poa polycolea
29 (28) Uppermost node in the basal third of the culm (30)
+ Uppermost node in the median third of the culm Poa sterilis
30 (29) Lowest lemma (2.8-)3-4.5mm long; spikelets 3-6.5mm long (31)
+ Lowest lemma (2-)2.3-3(-3.2)mm long; spikelets usually 3-4mm long Poa attenuata
31 (30) Very glaucous plant 10-25cm high (rarely higher); uppermost node in the lowest sixth of the culm
+ Green or glaucous plant, usually 25-50cm high; uppermost node about a third the way up the culm Poa versicolor subsp. araratica
 

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