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Solitary herb with a very short, subterranean caudex, simple or more often with short vertical branches, each ending in a leaf rosette at ground level. Flowering stems (scapes) erect, (2)3–8(10) cm, 0.5–1.0(1.2) mm broad, singly or sometimes several from rosettes, pubescent with patent, articulate, glandular hairs shorter than the stem diameter, hairs usually purple, at least with purple gland tips and cell walls.
Leaves alternate, all (except bracts) basal in rosettes, 1.2–2.0 × 0.4–1.2 cm. Blades obovate with rounded apex and narrowing more or less abruptly to a short petiole, coarsely dentate with obtuse triangular teeth as broad as or broader than wide.
Inflorescence of usually 2–4 flowers in a short, capitate raceme. Bracts below each inflorescence branch entire, narrowly ovate.
Flowers radially symmetric with 5 free sepals and petals. Sepals 3–4 × 1.5–2 mm, broadly ovate or obovate. Petals 3–4 × 1–2 mm, narrowly obovate, non-overlapping, 1.2–1.5 times as long as sepals, white or pink. Stamens 10. Gynoecium semi-inferior, of two carpels, split apically and with 2 styles.
Capsule with two beaks bending more than 90° outwards when ripe. Numerous seeds.
Sexual reproduction by seeds; no vegetative reproduction. The flowers are small and little visible and self-pollination is assumed to be the main mode in Svalbard. Flowering and seed-set are assumed to be fairly regular. Abundant seed germination from seed bank (Cooper et al. 2004).
Capsules have apical opening which ensures that the seeds only are dispersed at a minimum wind speed. Seed dispersal is often after the first snow fall, which increases the dispersal distance as the seeds are blown across a smooth surface (Savile 1972). Seeds are also dispersed by animals, e.g. geese, that selectively feed on capsules (Prop et al. 1984).
Micranthes nivalis may superficially be similar to M. tenuis but the two differ in several characters: Micranthes tenuis has more slender scapes which appears almost glabrous when seen without a hand lens, i.e., with sparse hairs < 1 mm long, the scape hairs are purple, also the cell walls, and less curly, rosette leaves are rounded with broad teeth pointing outwards, the inflorescence is more open and has branches with single flowers, and the beaks of the capsule bend back (more than to 90°); M. nivalis has comparatively stout scapes that are distinctly pubescent with hairs > 1 mm long, the scape hairs are curly, white and only purple at the very tip, the rosette leaves are more rhombic with narrower teeth pointing somewhat forwards, the inflorescence is more compact with several densely clustered flowers per branch, and the beaks of the capsule bend out but not back (up to 90°).
Of the four species of Micranthes in Svalbard, M. foliolosa and M. hieraciifolia are easily separable from the two others and from each other even by their leaves. Micranthes foliolosa has characteristic, obovate or obcuneate leaves with a few triangular teeth in the distal 1/3 only, and the leaves are thin and glabrous; M. hieraciifolia has ovate or lanceolate, subacute or acute leaves with sparse, shallow teeth along the sides, and the leaves are thick and with white, articulate hairs along the margins and on the lower surface. Micranthes nivalis and tenuis both have thick, rounded leaves with obtuse, forward pointing teeth, and they are not easily separable on their leaves alone. However, whereas M. nivalis has a fair amount of white and often some brown hairs along the leaf margins and on the lower surface, M. tenuis has only a scattering of very dark brown hairs on the lower surface.
Snowbeds and moist soil slopes, shallow mires. Predominantly on fine-grained substrates (clay, loam and fine sand). Micranthes tenuis is a specialist of moist–wet snowbeds and often confined to the coldest vegetation types in a terrain. Largely indifferent as to soil reaction (pH) but perhaps more rare in areas with acidic substrates only.
Frequent in all zones and sections. The species is known from all major islands, incl. Bjørnøya, and from several smaller ones.
The general range is circumpolar, restricted to the arctic zones and to mountains in the boreal zones, in Europe south to S Norway.
The group of Micranthes nivalis, M. tenuis, and two relatives (the Americans M. rufopilosa (Hultén) D.F.Murray & Elven and M. gaspensis (Fernald) Small, see Murray & Elven in print) has not been fully investigated as to molecular variation, but the two species present in Svalbard have been studied in Canada (Healy & Gillespie 2004). Morphologically, the two keep distinct, even when growing in close vicinity (Elven et al. 2011). Whereas M. tenuis is a diploid (2n = 20), M. nivalis is a hexaploid (2n = 60), and there is only a single substantiated report of a tetraploid (from Yukon, Canada). Until recently (after 2000), the majority of North American authors did not accept M. tenuis and M. nivalis as different, whereas these two have been accepted as independent species in N Europe for at least the last 60–80 years. Hybrids have been proposed now and then but never confirmed. The current evidence is that they are two well different species, often co-occurring in areas (but rarely within sites due to the different ecological demands), but never or very rarely forming any transitional forms.
Cooper, E.J., Alsos, I.G., Hagen, D., Smith, F.M., Coulson, S.J. & Hodkinson, I.D. 2004. Recruitment in the Arctic: diversity and importance of the seed bank. – Journal of Vegetation Science 15: 115–124.
Healy, C. & Gillespie, L.J. 2004. A systematic analysis of the alpine saxifrage complex (Saxifragaceae) in the Canadian Arctic Islands using morphology and chloroplast DNA data. – Canadian Field-Naturalist 118: 326–340.
Murray, D.F. & Elven, R. In print (2015). Micranthes rufopilosa (Hultén) comb. nov.: an alpine species from Alaska and Yukon. – Journal of the Botanical Research Institute of Texas.
Prop, J., van Erden, M.R. & Drent, R.H. 1984. Reproductive success of Barnacle Goose Branta leucopsis in relation to food exploitation on the breeding grounds, western Spitsbergen. – Norsk Polarinstitutts Skrifter 181: 87–117.
Savile, D.B.O. 1972. Arctic adaptations in plants. – Canada Department of Agriculture Research Branch Monograph 6. 81 pp.