The Flora of Svalbard

No means of 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 quite  regular. 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 seed capsules (Prop et al. 1984). Secondary dispersal by water or wind. Abundant seed germination from seed bank (Cooper et al. 2004).

Micranthes tenuis may be very similar to M. nivalis, but differs by having a more slender scape which appears almost glabrous when seen without a lens, whereas the scape of M. nivalis is distinctly pubescent, especially the upper 1–2 cm below the inflorescence. Stem hairs in M. tenuis are purple, also the cell walls, and shorter and less curly than those of M. nivalis which are purple only on the glands. Rosette leaves of M. tenuis are rounded with broad teeth pointing outwards, whereas those of M. nivalis are more rhombic with narrower teeth pointing somewhat forwards. The inflorescences of M. tenuis have branches with single flowers, whereas each branch in the inflorescence of M. nivalis usually carries several flowers. The capsule beaks of M. tenuis are also bent more strongly backwards than those of M. nivalis.

Of the four species of Micranthes in Svalbard, M. foliolosa and M. hieraciifolia are easily separable even on 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, multicellular hairs along the margins and on the lower surface. Micranthes nivalis and M. 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 only has a scattering of very dark brown hairs on the lower surface.

Not thermophilous, and often occupying the climatically less favourable sites in an area. Almost confined to snowbeds and shallow mires. Sometimes also in moist slopes with abundant soil. In poorly or rarely moderately drained soil, usually fine-grained (clay, loam, fine sand). Seems to be quite indifferent to soil reaction, but perhaps more rare in the acidic areas. Requires abundant protection from snow during winter, and not occurring at exposed sites. Probably little grazed by reindeer or geese.

The group of Micranthes nivalis, M. tenuis, and perhaps 1–2 relatives (the American M. rufopilosa (Hultén) A.E.Porsild and M. gaspensis (Fernald) Small), 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 the Yukon Territory, Canada) possibly from the related M. rufopilosa. Until recently (after 2000), the majority of North American authors have not accepted M. tenuis and M. nivalis as different, whereas these two have been accepted as independent species in northern 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.

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 Polarinstitutt Skrifter 181: 87−117.

Savile, D.B.O. 1972. Arctic adaptations in plants. – Canada Department of Agriculture Research Branch Monograph 6. 81 pp.