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Life span

Perennial, moderately long-lived.    

Growth form

Solitary graminoid herb growing in small, dense tussocks with all branching inside leaf sheaths (intravaginal, i.e., no runners or stolons). Culms to 10 cm or more, spreading or sometimes prostrate on the ground (very rarely erect), smooth and glabrous. Base of shoots surrounded by a cylinder of firm, shiny, pale yellowish grey withered leaf sheaths.    

Leaf

Leaves with keel and narrowly folded (convolute), smooth and glabrous. Basal leaves 3–8 cm long, usually much shorter than culms, narrow, 0.5–1.5 mm broad, abruptly tapering at the apex. Culm leaves 2–3, similar to basal leaves but with slightly inflated sheaths and much reduced blade, 0.4–1 cm long, the flag leaf blade attached below the middle of the culm. Ligula 0.5–1 mm, acute.    

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, ovate panicle 1–2 × 0.5–1.5 cm, occupying less than 1/5 of culm length. Panicle with 3–5 nodes with 2 branches at each of the lower nodes. Branches 1–5 mm, smooth, each with 1–3 spikelets. Spikelets 6–7 × 2.5–3.5 mm, with 3–6 flowers. Bracts (glumes and lemmas) with less distinct keel than in many other species of Poa. Glumes acute, smooth and glabrous, purplish (rarely greenish or pale lilac), the lower glume 3.2–3.7 mm, less than 1/2 the length of the spikelet, narrowly lanceolate, with 1 vein, rarely two short lateral veins, the upper glume 3.6–4.2 mm, 1/2 the length of the spikelet or more, more broadly lanceolate or oblanceolate, with 3 veins. Lemmas 3.0–3.3 mm, subacute, often with a lacerate apex (a character in Svalbard Poa shared with P. glauca and P. hartzii), with 3–5 veins, villous on and between veins except for the distal, hyaline part, purplish (rarely pale lilac or pale green) with a broad white and/or bronze yellow hyaline margin. Paleas shorter than lemmas and with pubescent veins. Anthers well developed, 0.4–0.7 mm.

Fruit

Fruit an achene (with one seed).    

Reproduction

Reproduction by seeds, probably sexual; no vegetative reproduction. Wind pollinated. Regularly flowering and with seed-set. Seeds germinates to 37 % (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 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 abbreviata is hexaploid (2n = 42). The pollen production is regular and the seed-set is probably mainly or entirely sexual but perhaps not very high. In a pilot study with a few plants of P. abbreviate, Haugen (2000) investigated seed-set in a laboratory situation without and with emasculation (removal of anthers).She found only 5 % seed-set (16 fruits from 311 florets) in control plants (not manipulated), only 2 % (3 fruits from 144 florets) in emasculated plants, indicating that sexual seed set dominates.

There is no special adaptation to seed dispersal, but the hairy lemmas may facilitate wind dispersal, perhaps also dispersal by animals (furs and feathers). Populations are usually rich in individuals, and the species is found in most sites and microsites where expected based on ecological requirements, suggesting an efficient dispersal and establishment.

Comparison

Poa abbreviata differs from P. arctica s. lat. and P. pratensis s. lat. in forming tussocks due to its intravaginal branching and total lack of rhizomes. It differs from the also tussock forming P. alpina in, e.g., its much narrower and more convolute leaves, lemmas densely hairy on and between the veins and with an often fringed apex, and in absence of a thick and dense 'socks' of several years' sheaths at the base of shoots; P. alpina has much broader and less convolute leaves that narrow abruptly in the apex, lemmas with long hairs on the veins only and with an evenly tapering apex, and presence of solid ‘socks’. It differs from P. glauca in being overall smaller (culm length rarely more than 10 cm), with intravaginal branching only, smooth panicle branches, and lemmas densely hairy; P. glauca is overall larger (culm length often ca. 20 cm), has a mixed intravaginal and extravaginal branching even if the plant usually is densely tussocky, the panicle branches are scabrous, often coarsely so, and the lemmas sparsely hairy on the veins only.

The species most similar to P. abbreviata, and probably its closest relative in Svalbard, is P. hartzii. They can be distinguished by the following characters: P. abbreviate is short-grown, culms rarely more than 10 cm, has very firm basal sheaths, shorter ligulas (0.5–1 mm), prostrate or ascending culms, leaves much shorter than half the length of culms, flag leaf blade attached below the middle of the culm, 1–3 spikelets per branch, and more broadly lanceolate glumes and lemmas; P. hartzii is more tall-grown, culms ca. 20 cm, has much less firm basal sheaths, longer ligulas (1.5–3 mm), erect culms, leaves nearly always more than half the length of the culms, the flag leaf blade attached at the middle of the culm, 2–5 spikelets per branch, and narrowly lanceolate glumes and lemmas.

Habitat

Poa abbreviata is among the most frost-tolerant of Svalbard plants, growing on outcrops and ridges with a scant snow cover in winter and exposed to the lowest temperatures and to abrasion by ice and snow crystals blown along the ground in strong winds. The buds are protected by the sheaths of leaf remains, and the tussocks catch snow and function as miniature snow banks, giving some protection. Also in the summer, its sites are harsh, often drying out and exposed to strong winds. The substrate is usually coarse (sand or coarser) and extremely well-drained, a difference from P. hartzii which has a preference for loam (silt) that may retain some water. The majority of sites of P. abbreviata are probably on basic substrates; the species is absent from many parts of Svalbard with acidic bedrock only.    

Distribution

Probably cryophilous. In all zones and in the weakly to clearly continental sections. The range is confined to three islands: Spitsbergen north of Van Mijenfjorden, especially the inner and middle fjord districts and on the north coast, the northern tip of Barentsøya, and Nordaustlandet where the species seems to occur scattered in most parts not covered by glaciers. The absence from all of Spitsbergen south of the Van Mijenfjorden and from the entire west coast except for the Ny-Ålesund area at Kongsfjorden is probably due to geology rather than climate.

The total range is probably very broadly amphi-Atlantic, encompassing the northernmost parts of the Canadian Arctic, N Greenland, Svalbard, and the northernmost parts of the Russian Arctic east to Taimyr. In Russia, the species has an interrupted range with its main occurrences in Franz Joseph Land, N Novaya Zemlya and Taimyr. The entire range is within the arctic zones.

Comments

The Svalbard material of Poa abbreviata belongs to the main arctic subspecies, ssp. abbreviata, which also is the subspecies of N Russia, Greenland and N Canada. The other subspecies, ssp. pattersonii (Vasey) Á.Löve, D.Löve & Kapoor (P. pattersonii Vasey)is Cordilleran (W North American mountains north to Yukon and Alaska), barely reaching the Arctic. No transitional forms are known and rank as two separate species may be merited. Apart from ssp. pattersonii, P. abbreviata is an unusually monomorphic species throughout its range.    

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.