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GROWTH FORM

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.

LEAF

Leaves with keel, flat or broadly folded (convolute), smooth or minutely scabrous in the margins. Basal leaves (1.5)2–6(8) cm long, 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).

Inflorescence a dense pyramidal panicle (2)3–5(7) × (2)3–4 cm, occupying less than 1/5 of culm length, often variegated in red and green. 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 to glumes 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. Stamens and fruits do not develop.

The entire spikelet above the glumes and perhaps the lowermost lemma is transformed into a bulbil with 2–3 small, green or reddish leaves, well developed before detaching from the mother plant.

FRUIT

Replaced by bulbils (vivipary).

REPRODUCTION

Vegetative reproduction by bulbils. Bulbils are produced in large amounts every year. Bulbils collected in Svalbard and stored one winter at -14°C in the Svalbard Global Seed vault, sprouted to 99 % (Alsos et al. 2013).

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-set, whereas higher ploidy levels are often (but not always) asexual with either seed-set without fertilization (agamospermy) or vegetative propagation by bulbils replacing the flowers in the spikelet (vivipary). Poa alpina var. vivipara is reported with moderately high chromosome numbers: 4/5×–7/8×, 2n = 32–52. The majority of bulbil-reproducing grasses seem to have their origin in inter-species hybrids but this is probably not the case in P. alpina. Variety vivipara does not differ from var. alpina in any observed feature except for the mode of reproduction. Infraspecific hybridization between ploidally different or otherwise incompatible strains of seminiferous P. alpina is suspected.

Bulbil reproduction may be a distinct fitness factor in humid arctic–alpine environments where long duration of the snow cover shortens the growth season. Bulbils shorten the period needed from propagule to reproducing individual appreciably compared with seeds. In a cultivation experiment in the field in the middle alpine belt at Finse, S Norway, var. vivipara developed from bulbil to reproducing plant within one year, whereas var. alpina took three years or more from seed to reproducing plant (Elven 1974). The reason may be the additional nutrients carried by a bulbil compared with a seed, and especially that it comes furnished with a functioning photosynthetic apparatus (green leaves) and often with emerging roots even before dispersal.

Bulbils are very efficiently spread by wind, often across snow banks or even glaciers (L. Ryvarden observ.). They keep their sprouting ability even after very rough handling across glaciers (also L. Ryvarden observ., across the Hardangerjøkulen Ice-Cap in S Norway). Bulbils do not depend much on good weather in the growing season; they usually develop whatever the conditions may be and very often sprout on the plant after a winter under a snow cover (R. Elven observ., Hardangerjøkulen area).

COMPARISON

The viviparous grasses of Svalbard belong to three genera: Deschampsia, Festuca and Poa. All viviparous Deschampsia and Festuca are tussock-forming with intravaginal branching only. All viviparous grasses with extravaginal branching and rhizome systems (mat-forming) belong to Poa (but note P. alpina with intravaginal branching). In addition, the leaves of viviparous Deschampsia and Festuca are either flat without a keel or involute (margins rolled together into a narrow cylinder), whereas the leaves of Poa have a keel and are flat or convolute (folded together). Also the glumes and lemmas in the spikelets differ: they have rounded backs in Deschampsia and Festuca, keeled backs in Poa.

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. These three species – P. alpina, P. arctica and P. pratensis – and hybrids that may involve them, are the only ones with proven viviparous plants among the taxa of Poa of Svalbard.

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. Easy to see is that they lack the dense ‘sock’ of old sheaths surrounding the base of the culms, and they have narrow, more strongly convolute and more evenly tapering leaves. None of them are known with bulbils.

HABITAT

Most common in heaths and meadows, along brooks and rivers, on slopes and more rarely on scree. On well drained or moderately drained, mixed or fine textured substrates of weakly acid or basic soil reaction (pH). Probably less frequent at strongly acidic sites. Requires snow protection during winter and rarely found in exposed sites. The viviparous reproduction enables the plants to complete the cycle of reproduction within a very short growing season. Hence, the viviparous form of P. alpina also grows in snowbeds in Svalbard but is not restricted to snowbeds to the same extent as it is in mainland Scandinavia. Probably grazed by reindeer and geese.

DISTRIBUTION

Common in the middle and north arctic tundra zones, perhaps transgressing into the polar desert zone in a few places; common from the weakly oceanic to the clearly continental sections. Found on all major islands, incl. Bjørnøya.

Poa alpina var. vivipara has a restricted, amphi-Atlantic range from Greenland eastwards to Novaya Zemlya and Polar Ural and southwards in Iceland, Fennoscandia, and the British and C European mountains. The range is always north of or higher up in the mountains than that of P. alpina var. alpina, but with a large overlap in ranges of these two varieties.

COMMENTS

There is little genetic difference yet found between var. vivipara and var. alpina (izoenzyme studies: 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). Nevertheless, the local and global ranges of the two varieties are markedly different and suggest significant genetic differences rather than modification only. One hypothesis could be that the genotypes of P. alpina present in the North Atlantic regions are more prone to turn into vivipary than those present in Canada, Alaska, and in Siberia east of the Urals. Variety vivipara is much hardier than var. alpina. At a global scale, however, var. alpina is the widespread race (se Distribution for P. alpina var. alpina).

LITERATURE

Alsos, I.G., Müller, E. & Eidesen, P.B. 2013. Germinating seeds or bulbils in 87 of 113 tested Arctic species indicate potential for ex situ seed bank storage. – Polar Biology 36: 819–830. Doi 10.1007/s00300-013-1307-7.

Elven, R. 1974. Artsinnvandring og vegetasjonsutvikling på resente morener i Finseområdet. – Cand. real. Thesis, Univ. Oslo, Oslo.

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.

PHOTOS Poa alpina var. vivipara

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Poa alpina vivipara 1 full
Poa alpina vivipara whole full

Observations in svalbard

__Herbarium specimen __Observation

ALL SPECIES OF THE GENUS Poa