The Flora of Svalbard

No means of vegetative reproduction. The plant flowers and fruits very regularly in Svalbard and produces a large amount of seeds which are assumed to ripen regularly. It is assumed that the species is mainly selfing (Brochmann et al. 1999). Seeds germinate 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 seed capsules (Prop et al. 1984). Secondary dispersal by water or wind.

Saxifraga rivularis and S. hyperborea are similar in most features and have been confused. They are most easily separated by the former regularly having subterranean runners (seen when digging the plants, but often lost in herbarium specimens), the latter never. Saxifraga rivularis therefore often grows in diffuse tussocks or small mats, whereas S. hyperborea always forms small, dense tussocks. The flowering stems of S. hyperborea are more often erect than those of S. rivularis, and more often reddish to purplish coloured, but these differences are not constant. Both species are easily separated from the related S. cernua and S. svalbardensis by their lack of bulbils in the axils of stem leaves and their much smaller flowers.

Saxifraga hyperborea is characteristic of moist flats, moist snowbeds, seepage areas, shallow mires, and shores (also upper parts of seashores). It may occur in manured areas like bird cliff meadows but more rarely than S. rivularis. The substrate may be fine-grained (silt, sand) or coarser (gravel). The plant is largely indifferent as to soil reaction (pH), but perhaps found more often on basic substrates than on acidic ones.

Saxifraga hyperborea is one of the diploid (2n = 26) parents of the tetraploid (2n = 52) S. rivularis, together with the diploid Beringian S. bracteata D.Don (Jørgensen et al. 2006). Saxifraga bracteata is restricted to the coasts of the North Pacific and the Bering Strait, and Jørgensen et al. (2006) assumed the origin of the allotetraploid to have taken place by hybridization of S. bracteata and S. hyperborea, followed by polyploidization, in the Beringian region. Even if S. rivularis and S. hyperborea are superficially similar, they differ distinctly in morphology, ploidy level, and molecular markers (Guldahl et al. 2005; Jørgensen et al. 2006; Westergaard et al. 2010) and deserve rank as two independent species. 

Saxifraga hyperborea is circumpolar. It is fairly uniform in the arctic parts. More morphological variation is found in the mountains surrounding the North Pacific, and a second species has been described from there: S. flexuosa Sternb. The molecular investigations to date have not given support to S. flexuosa as a species separate from S. hyperborea (Jørgensen et al. 2006).

Brochmann, C. & Steen, S.W. 1999. Sex and genes in the flora of Svalbard - implications for conservation biology and climate change. – Det Norske Videnskaps-Akademi. I. Matematisk Naturvitenskapelig Klasse, Skrifter, Ny serie 38: 33−72.

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.

Guldahl, A.S., Gabrielsen, T.M., Scheen, A.-C., Borgen, L., Steen, S.W., Spjelkavik, S. & Brochmann, C. 2005. The Saxifraga rivularis complex in Svalbard: Molecules, ploidy and morphology. – Flora 200: 207–221.

Jørgensen, M.H., Elven, R., Tribsch, A., Gabrielsen, T.M., Stedje, B. & Brochmann, C. 2006. Taxonomy and evolutionary relationships in the Saxifraga rivularis complex. – Systematic Botany 31: 702–729.

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.

Westergaard, K.B., Jørgensen, M.H., Gabrielsen, T.M., Alsos, I.G. & Brochmann, C. 2010. The extreme Beringian/Atlantic disjunction in Saxifraga rivularis (Saxifragaceae) has formed at least twice. – Journal of Biogeography 37: 1262–1276.