Poa pratensis L., Sp. Pl. 1: 67-68, 1753.
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https://dx.doi.org/10.3897/phytokeys.15.3084 |
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https://treatment.plazi.org/id/89294A68-E510-5948-A460-8C2D0091F6F8 |
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Poa pratensis L., Sp. Pl. 1: 67-68, 1753. |
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16. Poa pratensis L., Sp. Pl. 1: 67-68, 1753. Fig. 17 View Figure 17 18 View Figure 18
Type:
Russia, Prov. Sanct-Petersburg, 5 km australi-occidentum, 26 Jun 1997, N.N. Tzvelev N-257 (conserved type: BM! designated by Soreng and Barrie 1998, 157; isotypes: B!, C!, CAN!, CONC!, H!, K!, KW!, L!, LE!, LIV!, MA!, MO!, MW!, NSW!, P!, PE!, PR!, S!, SI!, TNS!, US-3456252!, W!).
Description.
Hermaphroditic. Perennials; tufted or not, rhizomatous, shoots solitary or tufted in part, tufts of narrow to medium girth and low to medium height, sometimes forming a dense turf (as in lawns), green, bluish-green, or bluish-gray-green; tillers extravaginal (basally cataphyllous), or also intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), with lateral and downward tending, cataphyllous shoots. Culms 5-70(-100) cm tall, erect or bases decumbent, leafy, terete or weakly compressed, smooth; nodes terete or weakly compressed, 1-2(-3) nodes exposed, proximal node(s) usually not exerted. Leaf sheaths terete to slightly compressed, glabrous or infrequently sparsely to moderately puberulent; butt sheaths papery, smooth, glabrous; flag leaf sheaths 2-20 cm long, margins fused 25-50% the length, 1.2-5(-6.2) × long as its blade; collars smooth, glabrous or ciliate along the margins; ligules 0.9-2(-3.1) mm long, abaxially smooth or scabrous, upper margin ciliolate or glabrous, apices truncate to rounded, infrequently obtuse; blades of cauline leaves 0.4-4.5 mm wide, flat or folded, to involute on the margins, soft and lax to moderately firm, abaxially smooth, glabrous, adaxially smooth or lightly scabrous, frequently with sparse, slender, erect to appressed, curving, sinuous or strait hairs to 0.2-0.8 mm long, broadly prow-tipped or some narrowly prow-tipped; blades subequal, or middle blades longest, flag leaf blades 1.5-10 cm; sterile shoot blades of extravaginal shoots like those of the culm, of intravaginal shoots, when present, sometimes distinctly narrower (0.4-1 mm wide), flat to involute. Panicles 2-15(-20) cm long, erect or nodding, loosely contacted to open, narrowly ovoid to narrowly or broadly pyramidal, sparse to moderately congested, with (25-)30 to over 100 spikelets; rachis with (1-)2-7(-9) branches per node; primary branches spreading early or late, terete or angled, smooth or sparsely to moderately densely scabrous; lateral pedicels usually 1/5-1/2 the spikelet in length, smooth, or sparsely to moderately densely scabrous, prickles fairly fine; longest branches (1-)2-9 cm, with 4-30(-50) spikelets, spikelets usually fairly crowded in distal 1/2. Spikelets 3.5-6(-7) mm long, to 3.5 × long as wide, lanceolate to ovate, laterally compressed, sometimes bulbiferous; florets 2-5, infrequently bulbous basally and leaf-like distally, hermaphroditic; rachilla internodes terete, mostly less than 1 mm long, smooth, glabrous; glumes narrowly lanceolate to lanceolate, infrequently broadly lanceolate, unequal to subequal, usually distinctly shorter than the adjacent lemmas, distinctly keeled, keels sparsely to densely, usually moderately, scabrous, infrequently smooth, apex acute, to acuminate; lower glumes 1.5-4(-4.5) mm long, 1-3-veined, narrowly lanceolate, occasionally weakly sickle shaped; upper glumes 2-4.5(-5) mm long, distinctly shorter to nearly equaling lowest lemma, 3-veined; calluses dorsally webbed, web well developed, sometimes with secondary tufts under each marginal vein, hairs 2-4 mm long, woolly; lemmas 2-4.3(-6) mm long, lanceolate, green or strongly purple colored, distinctly keeled, keels and marginal veins long villous, intermediate veins glabrous or infrequently short villous to softly puberulent, between veins glabrous, smooth or finely muriculate, smooth or lightly scabrous above, intermediate veins prominent, margins narrowly to broadly hyaline, apices acute; paleas scabrous, medially sometimes softly puberulent over the keels, intercostal region narrow, glabrous, or rarely very sparsely and minutely hispidulous. Flowers chasmogamous; lodicules 0.35-0.5(-0.7) mm long, broadly ovate, with a short lateral lobe about midpoint; anthers 1.2-2 mm long, infrequently aborted late in development and ca. 1 mm long. Caryopses 1.5-2 mm long, elliptical in side-view, slightly laterally compressed, subtrigonous in cross-section, brown, sulcus broad, shallow, hilum 0.2 mm long, round to oval, grain adherent to the palea. 2 n = 28-147.
Distribution.
The species is distributed worldwide but absent from tropical countries except in high mountains, or where introduced. In Mexico, the species is known from Baja California, Chihuahua, Coahuila, Distrito Federal, Hidalgo, Mexico, Nuevo León, San Luis Potosí and Veracruz. Poa pratensis subsp. agassizensis and subsp. alpigena are possibly native to Mexico.
Ecology.
The facultatively apomictic, mostly high polyploid species inhabits cool mesic to frigid climates, is often seeded for pastures and lawns, and is easily established outside of cultivation since it tolerates disturbance. In Mexico, it occurs from 10-3650 m. Flowering May to July.
Discussion.
Even though the species is highly plastic and tends to look a bit odd in low latitudes, we made an attempt to sort out the subspecific forms in Mexico. The results were unsatisfactory. We have identified a few specimens that match the typical forms, but we could not confidently place most of the material into subspecies. Poa pratensis is primarily a high polyploid and facultatively apomictic ( Clausen 1961). It is a common circumboreal species with numerous strains that are treated as species by some authors and as subspecies by others. In Russia (including the former Soviet States) the decision of whether to recognize the various morphological "forms" as subspecies or as distinct species has changed ( Tzvelev 1976, Czerepanov 1995) in favor of species, while in the UK Cope and Gray (2009) in the United Kingdom, and Portal (2005) in France Belgium and Switzerland have gone with subspecies. Stoneberg-Holt (2004) correlated morphology and ploidy-level in samples of Poa pratensis collected mainly across Eastern Europe and in Montana in the USA, and grown in a common garden with and without shade. She concluded that there was a continuum of morphological forms that grade from one extreme to another. Plants with predominantly very-fine, moderately firm (form retaining) intravaginal-leaved shoots, and low polyploidy (2n = 28-42) are referable to subsp. angustifolia; these grade into plants with some intravaginal-leaved shoots that are mostly soft-bladed and mainly of middle-ploidy (2n = 42-56) that are referable to subsp. pratensis; these grade into plants with all or most shoots extravaginal, fairly broad-bladed, of mainly higher ploidy (2n = 58-144) referable to subsp. irrigata. Selections by plant breeders from across the range of these forms are all evidently introduced into North America for pastures, soil stabilization, and lawns. However, the cultivated forms have been selected from forms attractive for lawns and most durable to mowing and trampling, and we are no longer dealing with geographic and ecologically differentiated natural taxa. Poa pratensis subsp. alpigena and subsp. agassizensis are probably native and are primarily mid-range polyploids. Our key to subspecies is presented for heuristic purposes; however, in practice it is difficult to draw a firm line between the tax a.
Key to the subspecies of Poa pratensis
| 1 | Vegetative shoots intravaginal (each with a well-developed, 2-keeled, longitudinally-spilt prophyll), and extravaginal shoots (each with a rudimentary prophyll and one to several cataphylls at the base); the involute blades often distinctly narrower than the flat ones | 2 |
| - | Vegetative shoots all extravaginal (or infrequently also with an intravaginal shoot), isolated or crowded (each extravaginal shoot with a rudimentary prophyll, and one to several cataphylls at the base) | 4 |
| 2 | Blades mostly flat and fairly soft, or a mixture of folded-involute moderately-soft to soft vegetative shoot blades, and flat or folded, soft culm blades; the adaxial surfaces of all blades usually glabrous; abaxial veins of intravaginal shoot blades slender, narrower than the intercostal surfaces; plants of pastures and parks and waste ground to subalpine | 6e. Poa pratensis subsp. pratensis |
| - | Blades of vegetative and culm shoots involute on the margins, moderately firm, and of fairly uniform width; the adaxial surfaces, at least of the vegetative shoot blades with sparse, elongated, weakly-appressed hairs; abaxial veins of intravaginal shoot blades slender to thick, narrower to broader than the intercostal surfaces; plants widespread | 3 |
| 3 | Blades ca. (0.8-) 1-2 mm wide (expanded), the longer vegetative shoot blades short less than 10 (-15) long; panicles contracted, branches smooth or sparsely scabrous; plants of mountain meadows, open forests, and subalpine | 16a. Poa pratensis subsp. agassizensis |
| - | Blades 0.4-1 mm wide (expanded), the longer vegetative shoot blades often exceeding 10 cm long; panicles loosely contracted to open, branches usually scabrous; plants of pastures, waste ground | 16c. Poa pratensis subsp. angustifolia |
| 4 | Extravaginal shoot blades fairly slender (1-2 mm wide), usually folded; vegetative shoots mostly isolated; panicles narrowly pyramidal, branches mostly smooth or sparsely scabrous, spikelets 3-4.5 mm long; plants of subalpine to alpine | 16b. Poa pratensis subsp. alpigen a |
| - | Extravaginal shoot blades generally broader (2-5 mm wide), flat or folded, often lax; vegetative shoots isolated or crowded; panicles pyramidal to broadly pyramidal, branches somewhat sparsely to fairly densely scabrous; spikelets 4-7 mm long; plants of lawns and parks and waste ground to low alpine | 5 |
| 5 | Glumes subequal, frequently pruinose, lower glumes (1) 3-viened, similar in shape to the upper glume, upper glumes often equal to the lowest lemma in length; panicles fairly sparsely flowered; collar margins and ligule abaxial surfaces commonly pubescent | 16d. Poa pratensis subsp. irrigata |
| - | Glumes unequal, infrequently pruinose, lower glumes 1 (3)-veined, narrower than the upper glume, upper glumes usually shorter than lowest lemma; panicles moderately densely flowered; collar margins and ligule abaxial surfaces usually glabrous | 16e. Poa pratensis subsp. pratensis |
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