Life span

Perennial, moderately long-lived.

Growth form

Solitary herb with a single root but often a branched caudex, growing as one-stemmed plants or as loose tussocks with several stems. Caudex branches ending in short, aerial shoots with several leaves close together in basal parts. Stems 5—15 cm, ascending to erect, with several leaves, the uppermost ones reduced in size and attached 1—2 cm below the inflorescences. Stems and leaves moderately to densely pubescent with small, multibranched (dendroid) hairs ca. 0.5 mm long and broad.

Leaf

Leaves alternate, up to 4(5) × 1.5(2) cm, very variable in size, ovate to obovate, coarsely dentate with (2)3—4(5) teeth per side, apex obtuse to subacute, green. Basal leaves gradually tapering at base into an indistinct petiole with small auricles. Stem leaves sessile and clasping (auricles large and half surrounding the stem).

Inflorescence

Inflorescence an open raceme with 5—15 flowers, short and broad in the flowering stage, 1—3 × 1—2.5 cm, elongating markedly during fruit maturation to (4)5—6 cm. Flowers ebracteate, except that the lowermost flower may be in the angle of the uppermost stem leaf.

Flower

Flowers radially symmetric, on pedicels 0.5—1 cm in flowering stage but elongating during fruit maturation, up to 1—1.5 cm broad with 4 free sepals and petals. Sepals (2.5)3.0—3.5 × (0.8)1.0—1,5 mm, ovate, obtuse, glabrous or sparsely hairy, green but often with violet tinge in the apical part, with narrow but distinct, white hyaline margins. The two outer sepals distinctly saccate at base (sac with nectar accumulation). Petals 8—10 × 2—4 mm, spathulate, with narrow claw and broad, obovate blade, apex rounded, not notched, white. Stamens 6; filaments 3—4 mm, not flattened; anthers ca. 0.5 mm. Gynoecium of 2 carpels, with 2 rooms separated by a secondary, hyaline wall.

Fruit

Fruit a long, narrow siliqua, (20)25—30(35) × 1.2—1.5 mm, glabrous, with 10—15 seeds in one row in each room. Seeds ca. 1 mm in diameter, flattened with a distinct wing.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. Flowers are adapted to insect pollination (size, nectar) and fertilization probably depends on insect visits. Seed production in Svalbard is regular. Seeds germinated to ca. 7 % in an experiment (Alsos et al. 2013).

The seeds have no special adaptations to dispersal except that their wings may facilitate some short-distance wind dispersal.

Comparison

The only (faintly) similar species in Svalbard are found in Draba but all species of Draba have short, ovate or oblong siliquas and significantly smaller flowers.

Habitat

The majority of stands in Svalbard, at least in Spitsbergen, are located in south-facing scree and bird cliff meadows. The species may be rather indifferent as to soil reaction (pH) but the finds have been made on circumneutral to basic substrates. The situation may be different on Bjørnøya where the species more often is found on dolomite or schist gravel on frost-patterned ground.

Distribution

Recorded from the middle and northern arctic tundra zones and the weakly oceanic to weakly continental sections. The distribution is restricted to Bjørnøya, where Engelskjøn & Schweitzer (1970) mapped 9 localities in the southern and mountainous part of the island, and to the west coast of Spitsbergen from Hornsund north to Liefdefjorden, reaching some distance into the fjords (in the Isfjorden area to Kapp Smith). This is an ‘oceanic’, west coast pattern shared by, e.g., Cerastium alpinumLuzula arcuataRanunculus glacialisRhodiola roseaSalix herbacea, and perhaps Sagina caespitosa.

What is considered the global distribution depends on how the species is circumscribed. Arabis alpina s. lat. is known from the E African volcanoes and the islands west of North Africa (the Canary Islands, Madeira) north to Greenland, Jan Mayen, Svalbard, and NW Europe, and east to W Asia. Arabis alpina s. str. is confined to C and N Europe and the surroundings of the North Atlantic.

Comments

Arabis alpina s. lat. is an extremely widespread species, present in several temperate and even tropical mountains in Europe, westernmost Asia, and Africa. It has an interesting and quite complicated phylogeography when its genetic variation is analysed (see Koch et al. 2006). However, all populations studied in the regions around the North Atlantic (Svalbard included) are monomorphic as to both molecular and morphological markers. One single genotype seems to have penetrated the Arctic and reached both the western (Iceland, Jan Mayen, Greenland) and the eastern parts (Scandinavia, Svalbard).

Literature

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.

Engelskjøn, T. & Schweitzer, H.J. 1970. Studies on the flora of Bear Island (Bjørnøya). I. Vascular plants. – Astarte 3: 1–36.

Koch, M., Kiefer, C., Ehrich, D., Vogel, J., Brochmann, C. & Mummenhoff, K. 2006. Three times out of Asia Minor: the phylogeography of Arabis alpina L. (Brassicaceae). – Molecular Ecology 15: 825–839.