Life span

Perennial, moderately long-lived.

Growth form

Solitary herb with basal caudex, more or less branched, with branches slightly to moderately covered by leaf remains and ending in often large rosettes in loose to open tussocks. Each rosette potentially with one flowering stem. Flowering stems ascending or erect, often very short at the beginning of flowering, 1–2 cm, but strongly elongating during and after flowering to 8–12 cm, occasionally 15–20 cm, in well-developed plants often with 1–2 entire or rarely dentate leaves, stems densely pubescent with stellate and often multibranched hairs into the inflorescence.

Leaf

Leaf rosettes up to 3–5 cm but often much smaller, occasionally larger. Leaves alternate, up to 20 × 8 mm, oblanceolate or obovate, entire or occasionally dentate in well-developed plants, mid vein not prominent, greyish green or grey (due to pubescence). Upper and lower leaf surfaces densely pubescent with short-stalked stellate hairs 0.3–0.5 mm in diameter, each hair with 3–5 main branches; petiole and lower part of margin occasionally with simple hairs up to 1.5 mm.

Inflorescence

Inflorescence a raceme with 5–15 flowers, elongating strongly in the fruit stage, sometimes up to 8–10 cm. Pedicels 4–8 mm in fruit stage, shorter than or about the same length as fruit, slender to moderately stout, attached at an angle with stem of 30–60°, pubescent with stellate and often multibranched and simple hairs.

Flower

Flower radially symmetric with 4 free sepals and petals. Sepals up to 3.5 × 2 mm, elliptic, greyish green with narrow to moderately broad white margin. Petals 3.5–5 × 2–3 mm, mostly more than twice as long as sepals, contiguous, patent (making the flower fully open), obovate or spathulate, slightly notched, white.

Fruit

Fruit a silicule 6–11 × 2.5–4 mm, erect or erectopatent, lanceolate or elliptic, not twisted, mid and lateral veins on valves not prominent, densely pubescent with short-stalked stellate hairs, greyish green. Style long, 0.9–1.2 mm. Seeds numerous, 10–12 in each room, medium brown, ca. 1 × 0.8 mm.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. Flowering and seed-set is regular in most years; mature seeds are often observed. Frequent outcrossing is assumed due to the large, open flowers adapted to insect pollination (Brochmann 1993; Brochmann & Elven 1993). Seeds germinate to 84 % (Alsos et al. 2013).

No special adaption to seed dispersal, probably mainly passively by wind over short distances.

Comparison

There are three species of Draba in Svalbard with only or predominantly stellate hairs: D. arctica, D. glabella and D. nivalis. The other white-flowered species either have simple hairs only (D. fladnizensis) or a mixture of simple, forked, cruciform, and/or multibranched hairs. Draba arctica and D. glabella have comparatively large, stellate hairs (0.3–0.5 mm), whereas D. nivalis has minute hairs (< 0.2 mm). Draba nivalis also has much smaller flowers and is generally a much smaller plant than the two others. Draba arctica differs from D. glabella essentially in that it has dense, stellate hairs also in the inflorescence, including the sepals, and on the fruits, whereas D. glabella usually has glabrous or subglabrous mid axis and pedicels and sepals and fruits either glabrous or with scattered, simple hairs. The stellate hairs on the leaves of D. arctica are usually more complex, with branched rays, than those of D. glabella with 4–5 simple rays. Those three species are therefore easily kept apart from all other Draba in Svalbard and also from each other, both in flowering and in fruiting stages.

Habitat

Most often in poorly vegetated areas such as on gravel ridges, in open patches in heaths, screes, gravel slopes, and road verges, but also in more densely vegetated environments such as bird cliff meadows, snowbeds with an early melt, upper parts of seashores, and sometimes in the uppermost parts of salt marshes. On well drained to slightly moist (bird cliffs, shores, snowbeds), mixed substrates with cirumneutral to basic soil reaction (pH). Primarily at exposed sites with high rates of insolation. Probably little grazed by reindeer and geese.

Distribution

Common in the middle and northern arctic tundra zones and in all sections. In Svalbard mainly restricted to Spitsbergen; reported from one site each on Edgeøya and Nordaustlandet.

The general range of Draba arctica is uncertain due to confusion with several morphologically similar species both in North America and in Russia. Our current data confirm the species from NE Canada (Ellesmere Land), Greenland and Svalbard. It has often been reported from arctic European Russia but we have not yet confirmed any specimens from there.

Comments

Draba arctica is a decaploid species (2n = 80, see Brochmann et al. 1993) within the circumpolar D. cinerea group, also including, among others, the mainly hexaploid (2n = 48) D. cinerea Adams and the octoploid (2n = 64) D. oblongata R.Br. A basic study of this group, also including data from Svalbard, is Böcher (1966). A subsequent study (Andersen 2003) is summarized by Andersen et al. (1999) and Elven et al. (2011). Here, D. arctica, D. cinerea, D. glabella, and also D. norvegica, were found to be consistently different in both molecular markers and morphology. Draba cinerea has not been recorded from Svalbard but is otherwise nearly circumpolar. Draba norvegica is recorded from E Canada, Greenland, Iceland, the Faeroes, N British Isles, mainland Fennoscandia, and N European Russia. Draba oblongata is confirmed from Greenland and North America, probably also present in significant parts of arctic Russia, but not (yet) confirmed from 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.

Andersen, B. 2003. Morphological and isoenzymatic variation in Draba arctica J. Vahl. and its relatives (Brassicaceae) in the North Atlantic region. – Cand. scient. Thesis, Univ. Oslo, Oslo.

Andersen, B., Elven, R., Nordal, I. & Spjelkavik, S. 1999. Species in the Draba 'hirta' complex in the North Atlantic area. – Skrifter Norske Videnskaps-Akademi. I. Matematisk Naturvitenskapelig Klasse, n. s. 38: 173–182.

Böcher, T.W. 1966. Experimental and cytological studies on plant species. IX. Some arctic and montane crucifers. – Biologiske Skrifter 14(7). 74 pp.

Brochmann, C. 1993. Reproductive strategies of diploid and polyploid populations of arctic Draba (Brassicaceae). – Plant Systematics & Evolution 185: 55–83.

Brochmann, C., Borgen, L. & Stedje, B. 1993. Crossing relationships and chromosome numbers of Nordic populations of Draba (Brassicaceae), with emphasis on the D. alpina complex. – Nordic Journal of Botany 13: 121–147.

Brochmann, C. & Elven, R. 1992. Ecological and genetic consequences of polyploidy in arctic Draba (Brassicaceae). – Evolutionary Trends in Plants 6: 111–124.

Brochmann, C., Soltis, D.E. & Soltis, P.A. 1992. Electrophoretic relationships and phylogeny of Nordic polyploids in Draba (Brassicaceae). – Plant Systematics & Evolution 182: 35–70.

Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF).