Life span

Perennial, potentially very long-lived.

Growth form

Both solitary and mat-forming herb forming cushions by shorter branches or forming extensive carpets by long prostrate perennial branches (slightly rooting). Tussocks or carpets 0.1–1 m broad or more. Lateral flowering branches very short, somewhat glandular pubescent.

Leaf

Leaves opposite, sessile, 2–6 mm long and broad, evergreen and thick, sessile, triangular, suborbicular, obovate or oblanceolate, ciliate towards the base and with an apical hydathode (pore) surrounded by white calcareous crust.

Inflorescence

Flowers singly in leaf axils.

Flower

Flowers radially symmetric, up to 1–3 cm broad, with 5 free sepals and petals. Sepals 2.2–3.2 × 1.8–2.7 mm, broadly ovate, ciliate and sometimes with stalked glands. Petals 5–15 × 3–8 mm, ovate, obtuse or acute, pink or purple. Stamens 10, purple. Ovary semi-inferior, of two carpels with two rooms, split apically.

Fruit

Fruit a capsule with numerous seeds.

Reproduction

Sexual reproduction by seeds; local vegetative reproduction by fragmentation of mats. Forming extensive prostrate mats with, to some extent, rooting branches. Detached branches can root and lead to new individuals but experimental propagation show large variation in rooting ability (20–90 %, Hagen 2002). The species is insect pollinated and commonly visited by small flies. Probably a mixed mater. Germinability of seeds is 60–70 % at 18–20°C, but only 2 % under natural outdoor conditions on a moraine (Alsos et al. 2013; Müller et al. 2011).

No special adaptation to seed dispersal. However, 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 animals, e.g. geese that selectively feed on seed capsules (Prop et al. 1984).

Comparison

This is the only Saxifraga in Svalbard with purple flowers, and non-flowering plants are also easily distinguished from all other Svalbard plants by their opposite, sessile, thick (evergreen) and more or less triangular leaves with a pore (hydathode), seen as a white dot, in the apex.

Habitat

Growing in a wide range of environments such as heaths and meadows, river and sea terraces, river bars, patterned ground, on tussocks in mires, cliffs, and scree. Often dominating along with Dryas octopetala in semi-dry heath vegetation. On well to poorly drained, mixed or fine textured soils with weakly acidic to basic soil reaction (pH). Growing in moderately exposed sites with wind abrasion (plants then often tussocky) but also in rather protected moderate snow beds with shortened growing season (plants then mostly mat-forming). Probably not much grazed by reindeer or geese.

Distribution

Common in all zones and sections. Probably the most widespread of all Svalbard vascular plants and often dominating in the vegetation. Also one of the most visible, especially early in the season when it flowers and may cover large stretches with its purple mats. Saxifraga oppositifolia has been recorded from almost every place in Svalbard visited and documented by botanists (and amateurs).

The general range is circumpolar and arctic–alpine, very widespread.

Comments

The total range of Saxifraga oppositifolia is wide, including the entire circumarctic area and many temperate mountain ranges south to the Alps, C Asia, and the central Rocky Mountains (Hultén 1973; Hultén & Fries 1986). A suggestion has been made to distinguish between pulvinate and prostrate plants as races (Andersson & Hesselmann 1901; Rønning 1996), respectively as ssp. reptans (G. Andersson & Hesselm.) Rønning and ssp. pulvinata (G. Andersson & Hesselm.) Rønning, but no genetic support has been found for such a division (Brysting et al. 1996). However, there may be a racial differentiation between tetraploid (2n = 52) Beringian and North American plants (ssp. smalliana (Engl. & Irmsch.) Hultén or ssp. glandulisepala Hultén) and diploid (2n = 26) European and W Siberian plants (ssp. oppositifolia). The former are characterized by, e.g., glandular sepals, the latter by eglandular sepals. The two constitute two main lineages in the molecular data analyzed (Abbott et al. 2000; Holderegger & Abbott 2003; Abbott & Comes 2004). Transitions between the two are known from arctic Canada and Greenland (Aiken et al. 2007), recognizable by a few glands on the sepals. Plants with some sepal glands are known from Svalbard as is the tetraploid chromosome number (from two counts). It is therefore feasible that both lineages (or subspecies) are represented also in Svalbard, ssp. smalliana probably only in transitional forms.

Literature

Abbott, R.J. & Comes, H.P. 2004. Evolution in the Arctic: a phylogeographic analysis of the circumarctic plant, Saxifraga oppositifolia (Purple saxifrage). – New Phytologist 161: 211–224.

Abbott, R.J., Smith, L.C., Milne, R.I., Crawford, R.M.M., Wolf, K. & Balfour, J. 2000. Molecular analysis of plant migration and refugia in the Arctic. – Science 289: 1343–1346.

Aiken, S.G. (ed.), Dallwitz, M.J., Consaul, L.L., McJannet, C.L., Boles, R.L., Argus, G.W., Gillett, J.M., Scott, P.J., Elven, R., LeBlanc, M.C., Gillespie, L.J., Brysting, A.K., Solstad, H., and Harris, J.G. 2007. Flora of the Canadian Arctic Archipelago: descriptions, illustrations, identification, and information retrieval. – [CD-ROM version] National Research Council Canada, Ottawa.

Alsos, I.G., Müller, E. & Eidesen, P.B. 2013. Germinating seeds or bulbils in 87 of 113 tested Arctic species indicate potential for ex situ seed bank storage. – Polar Biology 36: 819–830. Doi 10.1007/s00300-013-1307-7.

Andersson, G. & Hesselman, H. 1901. Bidrag till kännedomen om Spetsbergens och Beeren Eilands kärlväxtflora grundade på iakttagelser under 1889 års svenska polarexpedition. – Bihang till Kungliga Svenska Vetenskaps-Akademiens handlingar 26: 1–88.

Brysting, A.K., Gabrielsen, T.M., Sørlibråten, O., Ytrehorn, O. & Brochmann, C. 1996. The Purple Saxifrage, Saxifraga oppositifolia, in Svalbard: two taxa or one? – Polar Research 15: 93–105.

Hagen, D. 2002. Propagation of native Arctic and alpine species with a restoration potential. – Polar Research 21: 37–47.

Holderegger, R. & Abbott, R.J. 2003. Phylogeography of Arctic–Alpine Saxifraga oppositifolia (Saxifragaceae) and some related taxa based on cpDNA and ITS sequence variation. – American Journal of Botany 90: 931–936.

Hultén, E. 1973. Supplement to Flora of Alaska and neighboring territories. A study in the flora of Alaska and the transberingian connection. – Botaniska Notiser 126: 459–512.

Hultén, E. & Fries, M. 1986. Atlas of North European vascular plants north of the Tropic of Cancer. I–III. – Cramer, Vaduz.

Müller, E., Cooper, E.J. & Alsos, I.G. 2011. Germinability of arctic plants is high in perceived optimal conditions but low in the field. – Botany 89: 337–348.

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.

Rønning, O.I. 1996. Svalbards flora. Ed. 3. – Oslo: Norsk Polarinstitutt.

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