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Solitary graminoid herb growing in tussocks, with branching both inside (intravaginal) and outside leaf sheaths (extravaginal) but without runners or stolons. Culms to 10–20 cm (on manured sites to 30 cm), erect (rarely ascending), glabrous, minutely scabrous beneath the panicle. Base of culms with pale greyish, withered leaf sheaths.
Leaves with keel, flat to moderately folded (convolute), smooth and glabrous. Basal leaves 5–10 cm long, narrow, 0.8–2.5 mm broad, tapering towards apex. Culm leaves 2(3), similar to basal leaves but with shorter blades 1.5–5 cm, the flag leaf blade attached below the middle of the culm. Ligula 1–2 mm, 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 or open panicle (2.5)3–5(6) × (1.0)1.2–1.7(2.0) cm, occupying 1/3–1/5 of culm length. Panicle with 4–6(7) nodes with (1)2–3 branches at each of the lower nodes. Branches relatively short, very scabrous, the longer ones with 3–4 spikelets. Spikelets 5–7 × 2–3 mm, with 3–5 flowers. Bracts (glumes and lemmas) with keels. Glumes acute, smooth, violet or purplish throughout or with brownish or yellowish hyaline apex. Lower glume 3.0–3.2 mm, usually longer than 1/2 the length of spikelet, lanceolate, with 1 vein; upper glume 3.2–3.7(4.0) mm, more broadly lanceolate, distinctly longer than 1/2 the length of the spikelet, with 3 veins. Lemmas 3.2–3.8(4.0) mm, acute, often with a lacerate apex (rarely found in other Svalbard species of Poa except for P. abbreviata and P. hartzii), with 3–5 veins and long, more or less straight hairs on veins, minutely scabrous between the veins, pale purplish with a broad, bronze yellow and white hyaline margin. Paleas with pubescent veins and shorter than lemmas. Anthers well-developed, 1.3–2.2 mm, or shrivelled (non-functional).
Fruit an achene (with one seed).
Reproduction by seeds, probably both sexual and asexual (agamospermy); no vegetative reproduction. Flowers and seems to set seed regularly; however, there are no reports of ripe seeds of this species from Svalbard (Eurola 1972; Alsos et al. 2013), Greenland (Sørensen 1941), or anywhere else in the Arctic (reviewed in Alsos et al. 2013). In spite of these germination results, seed-set must be frequent also under natural conditions in Svalbard as this species is a regular colonizer of open ground, in Svalbard as everywhere else in the Arctic. Young plants, obviously sprouted from seeds, are commonly observed. This should be a warning to those extrapolating observations about absence of seed-set and seed germination in arctic plants.
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 (pseudovivipary). Poa glauca is mainly or entirely a decaploid species in Svalbard (2n = 70) and the seed-set is probably mixed sexual and asexual. The anthers and pollen are well developed in many plants, aborting in other plants (without loss of seed-set). In the study of Haugen (2000), 68 % of investigated plants had well developed anthers with seemingly functional pollen, 32 % had shrivelled (aborting) anthers and no pollen. Indirect evidence of sexuality is the presence of several and very frequent assumed hybrids with other species of the section (sect. Stenopoa) throughout its range outside Svalbard, but no other species of this section is present as native in Svalbard. Haugen (2000) investigated seed-set in a laboratory situation without and with emasculation (removal of anthers) in a pilot study of a few plants of Svalbard P. glauca. She found 18 % seed-set (139 fruits from 756 florets) in control plants (not manipulated), 9 % (41 fruits from 447 florets) in emasculated plants, suggesting potentially fairly high levels of both sexual and asexual seed-set.
There is no special adaptation to fruit dispersal, and most dispersal is probably passive (fruits inside florets blown along the ground). The species is common almost everywhere where ecological conditions are suitable (in Svalbard and almost everywhere else in the Arctic), and both dispersal and establishment is assumed to be efficient.
Poa glauca differs from both P. arctica s. lat. and P. pratensis s. lat. in its absence of stolons, much smaller panicles with few spikelets, and strongly scabrous panicle branches (smooth in P. arctica, often slightly scabrous in P. pratensis). It differs from P. alpina in, e.g., its much narrower leaves, lack of a distinct basal sheath of several years of leaf remains, and in a much smaller panicle with shorter and much more scabrous branches. From P. abbreviata and P. hartzii it differs most distinctly in presence of extravaginal shoots and the scabrous panicle branches but also in lemmas not densely hairy both on and between the veins.
Mistaking this Poa for a Puccinellia, especially P. angustata, is possible because they share the lacerate lemmas. However, all species of Puccinellia have rounded backs of bracts (glumes and lemmas).
Poa glauca is mostly found in sites with some open ground, on everything from coarse gravel and among blocks to fine-grained substrates (sand, silt) but most frequently on coarser, well-drained substrates. It is never found in permanently wet sites but may tolerate occasional inundation on gravel bars in rivers. It is confined to substrates with circumneutral or basic soil reaction (pH) in Svalbard, absent from all the districts with only acidic soils. It may form large tussock on fertilized sites.
Moderately thermophilous. Poa glauca is concentrated to areas with a relatively warm climate in the middle and northern arctic tundra zones and the weakly and clearly continental sections. The range is confined to the islands of Spitsbergen and Nordaustlandet. In Nordaustlandet it is found in the most favourable site known in that island: Floraberget (the "Flora Cliff") at Murchisonfjorden, Gustav V Land. In Spitsbergen there are single occurrences and very small locality groups at Van Mijenfjorden, on Ossian Sarsfjellet in Kongsfjorden, and at Liefdefjorden. Except for these, the entire range is within the middle and interior parts of the two major fjords with middle arctic tundra: Isfjorden and Wijdefjorden. It is a common species in these two areas.
Outside Svalbard, Poa glauca is one of the most widespread of all arctic plants, present in almost every area (including the small, isolated dot of Jan Mayen island), and also with extensive ranges in temperate mountains south to S Europe, the Caucasus, C Asia, and the southern Rockies.
Poa glauca belongs to the species-rich and complicated section Stenopoa, including, e.g., the more temperate species P. nemoralis and P. palustris (and should probably include also P. compressa currently assigned to section Tichopoa). Together with those of the American section Secundae these species constitute a major northern temperate to arctic complex with a reticulate morphological variation pattern combined with extensive variation in ploidy levels (from diploid to more than decaploid) and assumed mixture of sexual and asexual seed production.
In a combined geographical, morphological and cytological investigation, Pálsson (1986) studied the transition between the more temperate P. nemoralis and the arctic-alpine P. glauca. He found a fairly smooth transition in morphological traits between the two species and an even increase of morphological traits from P. glauca with increasingly northern location and increase in chromosome number. The transition from the mainly di- and tetraploid (2n = 24, 28) temperate P. nemoralis to the mainly decaploid (2n = 70) high arctic P. glauca appeared as a cline rather than as two distinct species. This is not a normal hybrid situation as the seed-set is high and regular throughout this transition. The highest ploidy levels and the most distinctive morphological features of P. glauca are found in the northernmost populations. These show little variation throughout the northern arctic parts of Europe, Asia and North America. However, as soon as one moves south to the southern arctic parts where P. nemoralis, P. palustris and several additional species in Russia are present, plants and even entire regional populations become difficult to assign to species. The Svalbard plants of P. glauca are among those most isolated from all relatives in sect. Stenopoa and probably therefore the least varying and the easiest to assign.
Propagation by bulbils (vivipary) is common in other asexual and mixed sexual and asexual complexes in Poa (e.g., in P. alpina and the P. arctica–pratensis group) but remains to be convincingly documented from sect. Stenopoa. However, a very few viviparous Svalbard populations are difficult to assign elsewhere. These have not yet been studied critically.
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.
Eurola, S. 1972. Germination of seeds collected in Spitsbergen. – Annales Botanici Fennici 9: 149–159.
Haugen, J. 2000. Possible hybrid origins of Poa hartzii and Poa arctica ssp. caespitans (Poaceae) investigated by morphology and isoenzymes. – Cand. scient. Thesis, Univ. Oslo, Oslo.
Pálsson, J. 1986. The Poa glauca/nemoralis complex in Iceland and its response to the environment. – Symbolae Botanicae Upsaliensis 27(2): 169–174.
Sørensen, T.W. 1941. Temperature relations and phenology of the northeast Greenland flowering plants. – Meddelelser om Grønland 125. 305 pp.