Life span

Perennial, probably comparatively short-lived.

Growth form

Solitary herb with a single stem or more often two or several flowering stems from a branched caudex. Subterranean runners never present. Most leaves basal. Pale, overwintering bulbil-shaped buds at stem bases. Flowering stems simple or branched in the inflorescence, erect, more rarely ascending, up to 10 cm but mostly shorter, sparsely hairy at base, with denser, 0.5–1 mm long, articulate, glandular hairs in the upper parts, hairs white, pink or purple, always with purple apical glands.

Leaf

Leaves alternate. Basal leaves long-stalked with petiole (0.5)0.7–1.2(1.5) cm, sheathing at base. Blade 0.3–1.0(2.0) × (0.3)0.6–1.0(1.2) cm, palmately lobed, with 3–5 obtuse or subacute lobes. One or two lower stem leaves, ± sheathing, short-stalked, palmately lobed, and one or two upper stem leaves, ± sessile, simple. No bulbils in leaf axils. Leaves glabrous or with sparse, long, articulate, glandular hairs.

Inflorescence

Terminal, with single flower or 2–3 flowers in a short cyme.

Flower

Flower radially symmetric with 5 free sepals and petals, half open with petals erectopatent. Sepals 1–2 × 0.8–1.8 mm, broadly ovate, obtuse, with articulate glandular hairs, especially on the lower part of the hypanthium, green or tinged reddish. Petals 3–5 × 1.3–1.8 mm, ca. 3 times as long as sepals, narrowly obovate, white with pink veins or pink throughout or more rarely purely white. Stamens 10. Ovary superior, of two carpels with two rooms, split apically.

Fruit

Fruit a capsule with numerous seeds.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. The plant flowers and fruits regularly in Svalbard and produces a large amount of seeds which are assumed to ripen regularly. It is assumed that the species is mainly self pollinated (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 water and by animals, e.g. geese that selectively feed on seed capsules (Prop et al. 1984).

Comparison

Saxifraga hyperborea and S. rivularis are similar in most features and have been confused. They are most easily distinguished by S. rivularis regularly having subterranean runners (easilyseen when digging the plants but often lost in herbarium specimens), S. hyperborea 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 tinged, but these differences are not constant. Both species are easily separated from the related S. cernua and S. svalbardensis by their much smaller flowers and their lack of bulbils in the axils of stem leaves.

Habitat

Saxifraga hyperborea is characteristic of moist plains, moist snowbeds, seepage areas, shallow mires, and shores (also upper parts of seashores). It may occur in manured areas such as bird cliff meadows but more rarely in such places than does 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.

Distribution

Present in all zones and sections. Frequent on Spitsbergen and parts of Nordaustlandet and recorded from several of the surrounding islands (e.g., Prins Karls Forland, Barentsøya, Kong Karls Land).

The general range is circumpolar in the arctic zones.

Comments

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 in the Beringian region by hybridization between S. bracteata and S. hyperborea followed by polyploidization. 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 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).

Literature

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 Polarinstitutts 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.