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GROWTH FORM

Mat-forming graminoid herb growing in often extensive stands due to horizontal, branched rhizome, typically with very slender rhizome branches of 2–8 cm between aerial shoots. Aerial shoots ascending from rhizome. Culms (5)9–15 cm, erect, smooth and glabrous. Base of culms with a few withered leaves more or less forming a loose sheath.

LEAF

Leaves keeled, flat to folded, smooth and glabrous. Basal leaves 3–7 cm long, shorter than culm, narrow, 0.5–1.5 mm broad, tapering at the apex. Culm leaves 3–4, blade 1–3 cm long, broader than leaves of vegetative shoots (1.3–2.2 mm), flag leaf blade attached near middle of culm but much variation due to developmental stage. Ligula 1–2 mm, obtuse, often lacerate.

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 narrowly elongate, rather compact panicle (2)2.5–3.5(5) cm long with erect to ascending branches; panicle occupying 1/3–1/4 of culm length. Panicle with 7–10 nodes and 3–4(5) branches at each of the lower nodes. Branches 5–15 mm long, smooth or very sparsely scabrous, the lower ones with 4–6(8) spikelets along much of the branch length. Spikelets difficult to measure due to very early development of flowers into bulbils, but smaller than in ssp. alpigena (probably ca. 3–3.5 × 2–2.5 mm), with 2(3) flowers. Bracts (glumes and lemmas) with keels, often fairly sharp. Glumes lanceolate to broadly lanceolate, acute, with 3 veins, green or distal and marginal parts turning into purple with a narrow, white hyaline margin. Lower glume 2.1–2.4 mm, smooth and glabrous, distinctly shorter than upper glume; upper glume 2.7–3.3 mm, ca. 4/5 of entire spikelet length (before development of bulbil), often scabrous on keel, otherwise smooth and glabrous. Lemmas 1.8–2.5 mm, broadly lanceolate, subacute to acute, with 5 more or less distinct veins, scabrous along keel, with dense, wavy (curly) hairs on the veins and keel but glabrous and smooth between the veins, with a small, loose tuft of cottony hairs at the base of the lemma, with same coloration as glumes but with broader hyaline margin. Paleas shorter than lemmas, with pubescent veins. Stamens absent in nearly all observed plants (Haugen 2000 reported a few).

The entire spikelet except for the glumes starts to turn into bulbils early in the season. Bulbils small, with narrow, dark purplish green leaves, but in great abundance making the panicle appear very bushy late in season.

FRUIT

Replaced by bulbils produced from spikelets in the panicle.

REPRODUCTION

Vegetative reproduction by bulbils. Poa pratensis ssp. colpodea forms stands locally by vegetative growth of the rhizome system and are spread over longer distances by bulbils (vivipary). No seed production has been observed or is assumed.

The bulbils are spread mainly by water and wind, in the latter case along the ground and especially in late autumn and early winter when the ground is frozen and often with a firm snow cover. Bulbils often end up in depressions in the terrain, sites that become wet during snow melt and often moist to wet throughout the growth season, i.e., suitable for germination and survival of this plant. For the adaptive features of bulbils compared with seeds, see Poa alpina var. vivipara.

COMPARISON

The viviparous grasses of Svalbard belong to three genera: Deschampsia, Festuca and Poa. All viviparous species of Deschampsia and Festuca are tussock-forming with intravaginal branching only. All viviparous grasses with extravaginal branching and rhizome systems (mat-forming) belong to Poa. In addition, the leaves of viviparous species of Deschampsia and Festuca are flat without a keel or involute (margins rolled together into a narrow cylinder), whereas the leaves of species 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.

Among the viviparous Poa, P. alpina grows in dense tussocks with intravaginal branching only, whereas the P. arctica–pratensis complex has extravaginal, horizontal and branched rhizomes and forms mats. Haugen (2000) found the following characters to separate between P. pratensis ssp. colpodea and the other bulbil-reproducing parts of this complex (P. arctica/pratensis viviparous): In ssp. colpodea culm length ca. 9–15 cm, panicle length 2.4–3.2 cm, panicle branches 1.3–7.0 mm, erect and sometimes sparsely scabrous, lower glume usually 3-veined, nearly as long as upper glume 2.6–3.5 mm, upper glume keel often scabrous, lemmas 0.7–0.9 mm wide, never hairy between veins, tuft (tomentum) at base of lemma moderately developed, and anthers usually missing; in the other subspecies: culm length 12–20 cm, panicle length 3.3–5.2 cm, panicle branches 6.1–14.1 mm, ascending or more or less spreading and smooth, lower glume often 1-veined, shorter than upper glume 3.3–3.8 mm, upper glume keel smooth, lemmas 0.9–1.0 mm wide, sometimes with some hairs between veins, tuft (tomentum) at base of lemma well-developed, and anthers often present but shrivelled. The measures deviate somewhat from those given by us in the description above. This is due to different samples of material being studied. Scholander (1934) emphasized another character: the smaller and much more numerous spikelets found in the panicles of ssp. colpodea compared with the others.

HABITAT

On moist, fine-grained substrates, on flat or gently sloping ground with periodic or constant seepage or high water levels, often together with the tetraploid morph of Dupontia fisheri. A weak competitor and never found in dense, tall-grown vegetation. Probably indifferent as to soil reaction (pH).

DISTRIBUTION

Cryophilous. In all zones but rare in the middle arctic tundra zone; in the transitional to clearly continental sections. This plant increases in frequency towards the northeast (into the harshest parts of Svalbard). It has been recorded from all the four major islands in the Spitsbergen group, being especially frequent in Nordaustlandet, and is also documented from Kong Karls Land. This is an easily overlooked (or ignored) plant and may have a denser and larger distribution in Svalbard than currently documented.

Poa pratensis ssp. colpodea is a high arctic specialist, otherwise reported from the northernmost parts of European Russia, Siberia, the Russian Far East, Canada, and Greenland, mainly in the 2–3 northernmost zones. We have observed plants in the field in several places in arctic Canada, Far East and Siberia, besides Svalbard, and they look the same everywhere.

COMMENTS

Poa pratensis ssp. colpodea is one of the more enigmatic of arctic plants. It was first described by Th. Fries in 1870 (see Elven et al. 2011) but its recognition as something apart from the main variation in the P. arctica–pratensis complex is due to Scholander (1934), specifying its characters based on an abundant material collected in the northeastern parts of Svalbard in 1931. Since then, the plant has been in and out of systematic treatments of Svalbard plants, depending on whether the author was a splitter or lumper.

This plant was included in the study of some Svalbard Poa by Haugen (2000) and compared with the tussock-forming P. abbreviata, P. glauca and P. hartzii and the more or less mat-forming P. arctica ssp. arctica, ssp. caespitans and viviparous P. pratensis ssp. alpigena. Haugen studied morphology, isoenzyme patterns, and reproduction. Surprisingly, it came out distinct from the entire P. arctica–pratensis complex in isoenzymes, in another main branch in an UPGMA classification with P. hartzii and P. glauca as its closest neighbours (Haugen 2000: 72). In the four investigated enzymes, it shared its AAT type with P. hartzii and to some degree P. glauca, its TPI type with P. glauca, whereas it had unique PGI and PGM types. Its isoenzyme phenotypes were in all cases simpler or just as complex as the patterns in the other investigated taxa, not suggestive of any very complicated hybridogeneous background from any among these.

In an UPGMA classification of the P. arctica–pratensis complex based on morphological characters, it constituted one of the first main clusters, whereas all other plants of the complex constituted the second cluster (Haugen 2000: 62). Other investigators have found the same in North America where McLachlan et al. (1989) found reason to recognize the plant in the Queen Elisabeth Islands in the Canadian Arctic Archipelago. Soreng (2007) accepted the subspecies for Flora of North America (however, he probably included all high arctic viviparous plants of the P. arctica–pratensis complex in this subspecies).

We then end up with accepting P. pratensis ssp. colpodea as a genetically probably quite distinct taxon but with some delimitation problems morphologically, mainly because there are few characters to study in viviparous plants. The data from isoenzymes support rank as a species apart from the P. arctica–pratensis complex rather than as a subspecies of P. pratensis. A more extended genetic investigation of this plant and its relatives, applying other and more differentiating molecular markers, might be rewarding.

LITERATURE

Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF).

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.

McLachlan, K.I., Aiken, S.G., Lefkovitch, L.P. & Edlund, S.A. 1989. Grasses of Queen Elisabeth Islands. – Canadian Journal of Botany 67: 2088–2105.

Scholander, P.F. 1934. Vascular plants from northern Svalbard with remarks on the vegetation in North-East Land. – Skrifter om Svalbard og Ishavet 62. 155 pp.

Soreng, R.J. 2007. Poa L. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico 24. Magnoliophyta: Commelinidae (in part): Poaceae, part 1: 486–601.

Observations in svalbard

__Herbarium specimen __Observation

ALL SPECIES OF THE GENUS Poa