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Solitary graminoid herb growing in dense tussocks with all branching inside leaf sheaths (intravaginal, i.e., no runners or stolons). Culms to 20 cm or taller, smooth. Base of shoots surrounded by several years' withered leaf sheaths in two opposite rows (distichous) as a dense, pale cylinder (‘sock’). Culms and leaves glabrous.
Leaves with keel, flat or broadly folded (convolute), smooth or minutely scabrous in the margins. Basal leaves 4–6 cm, comparatively broad (3–5 mm) for almost their entire length, abruptly tapering at the apex. Culm leaves 2–3, similar to basal leaves but shorter, the flag leaf blade attached near the middle of the culm. Ligula 1.5–2(3) mm, obtuse or subacute.
INFLORESCENCE AND FLOWER
The units of the inflorescence of Poaceae are the spikelets, nearly always numerous in a panicle or spike-like inflorescence. Spikelets are composed of 2 glumes (bracts for the spikelet) and one or more flowers (the term used below) or rather floral units often named ‘florets’ because we do not know what is the exact flower. A flower or floret is composed of a lemma with 1 mid vein (probably the floral bract), a palea with 2 mid veins (either 2 fused bracteoles or perhaps 2 fused perianth leaves), 3 small organs called ‘lodiculae’ and essential in the opening of the flower at anthesis (possibly transformed perianth leaves or transformed stamens), 3 stamens (mostly), and a gynoecium of 2 fused carpels with 2 feathery stigmas and one seed.
Inflorescence a dense pyramidal panicle 1.5–3(3.5) × 1.5–2.5(3) cm, often variegated in red and green, occupying less than 1/5 of culm length. Panicle with 4–7 nodes with 2–3 branches at each of the lower nodes. Branches 10–30 mm, smooth or minutely scabrous, ascending and/or spreading. Spikelets 4–6 × 2.5–3.5 mm, with 3–4(6) flowers. Bracts (glumes and lemmas) with very distinct, often slightly scabrous keels and 1–3(5) veins. Glumes 2–3 mm, ca. 1/2 the length of the spikelet, broadly ovate, broadly and evenly tapering towards apex, red or greenish with bronze yellow and white hyaline margin, glabrous. Lemmas 2.5–4 mm, similar in shape and colour but with long, silky hairs on mid vein and lateral veins. No tuft of hairs at the base of the lemma. Paleas shorter than lemmas, with pubescent veins. Anthers 1.4–2 mm, usually well developed, dehiscent.
Fruit an achene (with one seed).
Reproduction by seeds, sexual and probably also asexual (agamospermy); no vegetative reproduction. Flowering regularly and probably with some seed-set but perhaps not all years.
In some grass genera, Poa among them, there is a fairly good correlation between ploidy levels and modes of reproduction. Diploids (mostly 2n = 14) and tetraploids (mostly 2n = 28) usually have sexual seed reproduction, whereas higher ploidy levels are often (but not always) asexual with either seed production without fertilization (agamospermy) or vegetative propagation by bulbils replacing the flowers in the spikelet (vivipary). Poa alpina var. alpina in Svalbard has high and irregular chromosome numbers (9–11×, 2n = ca. 63–77). The seed-set is assumed to be mainly asexual. However, pollen production is normally good and some degree of sexuality is assumed, also because at least two hybrids are documented with P. alpina as parental.
There is no special adaptation to seed dispersal, and the few known native stands in Svalbard are all fairly small in area, suggesting restricted and only local dispersal.
Poa alpina differs from P. arctica s. lat. and P. pratensis s. lat. in its intravaginal branching; the two others have extravaginal branching with rhizomes breaking out at the base of the basal leaf sheaths. This also means that P. alpina is much more densely tussocky than the two other species which grow in extensive mats or more loose tussocks. Another difference is the shape of the leaves, broad and abruptly tapering at the apex in P. alpina, narrower and more evenly tapering in the others, and in the shape of glumes and lemmas, broad and broadly acute in P. alpina, narrower and more acuminate in the others.
The other tussock forming species of Poa in Svalbard – P. abbreviata, P. hartzii and P. glauca – differ in more features and are rarely confused with P. alpina. All three have small, compact tussocks without the distinct ‘socks’ of sheaths, with much narrower leaves (densely convolute and 0.5–2.5 mm broad vs. flat or broadly convolute and 3–5 mm broad in P. alpina), leaves also more evenly tapering, and the panicles and spikelets are much smaller.
All native stands found in Svalbard are located on slopes with meadows and stable scree exposed to high insolation rates, or to the surroundings of warm springs, i.e., the climatically most favourable sites in all of Svalbard. On well drained fine textured or mixed substrates with circumneutral or basic soil reaction (pH). Probably not growing under acidic conditions. Requiring snow protection during winter. Grazed by reindeer and geese.
In addition, the species has been found on disturbed ground a few places in settlements and near cabins, obviously introduced.
Native and introduced. Thermophilous. As native found in the middle arctic tundra zone and the weakly and clearly continental sections. The known native stands of Poa alpina var. alpina in Spitsbergen are all located in very favourable sites: the close surroundings of the warm springs at Bockfjorden (Haakon VII Land) and three southwest-facing slopes with a very high number of other thermophilous indicator species at Sassendalen (Sabine Land) and Wijdefjorden (Ny-Friesland). The populations may be relicts from the Holocene Hypsithermal (8000–4000 BP).
Seminiferous Poa alpina has been documented from three other sites where we assume it to have been introduced: Tunheim on Bjørnøya, observed in 1957 and 1983 (Rønning 1959; Engelskjøn 1986), Hiorthhamn at Adventfjorden 1939 (Nordenskiöld Land) and Ny-Ålesund at Kongsfjorden 1939 (Oscar II Land), both the latter reported by Hadač (1941).
The global range of Poa alpina var. alpina is nearly circumpolar in the boreal and southern arctic zones but with a huge gap in Siberia east of the Jenissei (but it occurs in the S Siberian mountains). The Svalbard occurrences are by far the most northern ones known in the world; in Russia it reaches the southern island in Novaya Zemlya, in Greenland the middle parts, and in Canada the central parts of the Arctic Archipelago, in all cases at latitudes 5–10° south of Svalbard.
See also var. vivipara.
There is little genetic difference between var. vivipara and var. alpina (Iversen 1992; Nordal & Iversen 1993). Iversen (1992) showed a high level of genetic variation (isoenzyme phenotypes) in viviparous Poa alpina, higher than in many sexual species. Transition between seminifery (seed-set) and vivipary (bulbil-set) has proved easy with temperature changes (see, e.g., Nygren & Almgård 1962, referring many pioneer works of A. Müntzing). For the possible adaptive effects of vivipary in the Arctic, see var. vivipara and the references in Elven (1974). Nevertheless, the local and global ranges of the two varieties are markedly different and suggest significant genetic differences rather than modification only. Variety vivipara is restricted to the North Atlantic regions from E Greenland east to Svalbard and south to Iceland, Scotland, and Scandinavia. It reaches very far north and high up in the mountains and is much hardier than var. alpina. At a global scale, however, var. alpina is the widespread race and the only race in NE European Russia, Siberia, the Russian Far East, Alaska, Canada, and W Greenland, but it does not reach far north into the Arctic (see above).
Elven, R. 1974. Artsinnvandring og vegetasjonsutvikling på resente morener i Finseområdet. – Cand. real. Thesis, Univ. Oslo, Oslo.
Engelskjøn, T. 1986. Eco-geographical relations of the Bjørnøya vascular flora. – Polar Research, n. s., 5: 79–127.
Hadač, E. 1941. The introduced flora of Spitsbergen. – Det Kongelige Departementet for Handel, Sjøfart, Industri, Håndverk og Fiskeri. 49 pp.
Iversen, A.P. 1992. En populasjonsbiologisk undersøkelse av Poa alpina L. – Cand. scient. Thesis, Univ. Oslo, Oslo.
Nordal, I. & Iversen, A.P. 1993. Mictic and monomorphic versus parthenogenetic and polymorphic – a comparison of two Scandinavian mountain grasses. – Opera Botanica 121: 19–27.
Nygren, A. & Almgård, G. 1962. On the experimental control of vivipary in Poa. – Kungliga Lantbrukshögskolans Annaler 28: 27–36.
Rønning, O.I. 1959. The vascular flora of Bear Island. – Acta Borealia, ser. A, 15: 1–57.