Life span

Perennial, potentially quite long-lived.

Growth form

Solitary herb with basal caudex slightly or moderately covered by leaf remains from previous years, branching into numerous, often large, rosettes in loose to open tussocks. Each rosette potentially with one flowering stem. Flowering stems ascending or erect, sometimes short at the beginning of the flowering, 1–2 cm, but strongly elongating during and after flowering to 15–20 cm or occasionally more, in well-developed plants with 1–2(3) dentate leaves. Stems moderately to densely pubescent with stellate, forked, and sometimes simple hairs in the lower part, often glabrous in the inflorescence.

Leaf

Leaf rosettes up to 7–8 cm, occasionally larger. Leaves alternate, up to 40 × 10 mm, oblanceolate or obovate, dentate in well-developed plants, occasionally entire in stunted plants, mid vein not prominent, pale to greyish green. Upper and lower leaf surfaces sparsely to moderately pubescent with short-stalked, stellate hairs 0.3–0.5 mm in diameter with 3–5 main branches, and where branches are simple or have slight secondary branching, occasionally in mixture with a few forked and/or simple hairs, petiole and lower part of margin often with simple hairs up to 1 mm.

Inflorescence

Inflorescence a raceme with 8–15 flowers, elongating strongly in the fruit stage, sometimes up to 8–10 cm. Pedicel 5–10 mm in fruit stage, about the same length as the fruit, slender to moderately stout, attached with scape at an angle of 20–30°, glabrous or occasionally pubescent as scape.

Flower

Flowers radially symmetric with 4 free sepals and petals. Sepals up to 3 × 1.8 mm, elliptic, pale greyish green with narrow to moderately broad white margins. Petals 3.5–6 × 2–3.5 mm, mostly more than two times as long as sepals, contiguous, patent (making the flower fully open), broadly obovate or spathulate, slightly notched, creamy white, rarely pale yellow.

Fruit

Fruit a silicule 7–12 × 2–3.5 mm, erect or erectopatent, lanceolate or narrowly lanceolate, sometimes twisted, mid and lateral veins on valves often prominent, glabrous or rarely with a very sparse pubescence of short simple or forked hairs, dark olive, greyish or brownish green. Style short, 0.1–0.2 mm. Seeds numerous, 10–14 in each room, medium brown, ca. 1 × 0.8 mm.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. Frequent outcrossing is assumed due to the large, open flowers (Brochmann 1993). Flowering and seed-set is regular in most years; mature seeds are often observed. The seeds germinated to ca. 54 % in an experiment (Alsos et al. 2013).

There are no special adaptations to seed dispersal.

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 only simple hairs (D. fladnizensis) or a mixture of simple, forked, cruciform, and/or multibranched hairs (D. lactea, D. norvegica, D. subcapitata). 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 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, up to the sepals, and on the fruits, and the stellate hairs usually have secondary branching; whereas D. glabella often has glabrous or subglabrous mid axis and pedicels and sepals and fruits either glabrous or with scattered, simple hairs and the stellate hairs usually have simple branches. These three species are therefore well distinguished from each other and from other white-flowered species of Draba, both in flower and in fruit stages.

Habitat

Usually in environments with little or intermediate vegetation cover such as scree, gravelly or moderately vegetated slopes, bird cliff meadows, but also often reported from disturbed sites, e.g., road verges, and on upper parts of seashores. On well drained to slightly moist (bird cliffs, shores) mixed substrates with circumneutral to basic soil reaction (pH), rarely on substrates with weakly acidic reaction. Growth sites usually moderately exposed to moderately protected, not including snowbeds.

Distribution

Moderately thermophilous. Iin the middle and northern arctic tundra zones and in the weakly oceanic to clearly continental sections. In Svalbard restricted to Spitsbergen where it is locally common in some parts, especially in the climatically more favourable parts along some of the western fjords (Isfjorden, Kongsfjorden), and to one site northernmost on Barentsøya.

The general range is circumpolar in the low arctic and boreal zones, and this is one of the most widespread of Draba species.

Comments

Draba glabella varies within broad limits in size and pubescence (degree and kinds). This octoploid species (2n = 64) is polymorphic and may well be heterogeneous, meaning that the species may consist of several parts where different parental low-ploid genomes partake. However, the Svalbard plants largely correspond in their morphology to those of N Fennoscandia, Greenland, and the neighbouring parts of Russia. Several studies have given support to D. glabella as major, independent species in the northern regions (Andersen 2003; Andersen et al. 1999; e.g., Böcher 1966; Brochmann et al. 1992, 1993; Elven et al. 2011). All these studies include considerations also of Svalbard plants.

The species is white-flowered throughout its range. However, a population in the Pyramiden area in Dickson Land, Spitsbergen, is characterized by distinctly pale yellow petals.

For the intricate questions of the correct names of D. glabella and D. norvegica, see Comments under D. norvegica.

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 polyploidy 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., 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).