Life span

Perennial, potentially quite long-lived.

Growth form

Solitary herb with basal caudex densely covered by marcescent leaf remains, branching into often numerous, small, densely clustered rosettes forming small, dense tussocks. Each rosette potentially with one flowering stem, up to 10 or more per tussock. Flowering stems erect, sometimes short at the beginning of the flowering, 1–2 cm, but elongating during and after flowering, to 4–10 cm, without or with a leaf, densely covered with minute stellate hairs up to and including the pedicels (glabrous in plants with glabrous or subglabrous leaves).

Leaf

Leaf rosettes 1–2.5 cm, occasionally larger. Leaves alternate, up to 8 × 2.5 mm, narrowly oblanceolate, obovate or broadly obovate, obtuse, entire, mid vein not prominent, pale green. Upper and lower leaf surfaces and margins densely covered by a grey-white pubescence of minute (< 0.2 mm), regularly stellate hairs with ca. 8 patent to erectopatent branches with abundant secondary branching (strong lens or microscope), rarely only with a rim of such hairs along the margin (‘subglabrous’) and very rarely glabrous; petiole or lower part of margin often also with a few simple hairs up to 0.5 mm.

Inflorescence and Flower

Inflorescence a raceme with 5–10 flowers, elongating in the fruit stage up to 5 cm. Pedicels (1)2–3 mm, less than half the fruit length, slender, attached with scape at an angle of 40–60º but regularly curved upwards, covered by stellate hairs (rarely glabrous).

Fruit

Fruit a silicule mostly 5–7 × 1–1.5 mm, erect or more often erectopatent, linear, narrowly elliptic, narrowly lanceolate or oblong, sometimes falcate or slightly twisted, glabrous or rarely with scattered, mostly stellate hairs, dark olive green. Style short, 0.2–0.5 mm. Seeds numerous, 10–12 in each room, pale brown, ca. 0.9 × 0.7 mm.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. The flowers are very small and Draba nivalis is known to be highly selfing (Brochmann 1993). Flowering and seed-set is regular in most years; mature seeds are often observed. Seeds germinate to nearly 90 % (Alsos et al. 2013).

There is no special adaptation to seed dispersal.

Grundt et al. (2006) found frequent sterility barriers between populations of D. nivalis in the circumpolar area. Crosses between populations from Svalbard, mainland Norway, Alaska and Greenland were included.

Comparison

There are three species of Draba in Svalbard with only or predominantly stellate hairs, all white-flowered: D. arctica, D. glabella and D. nivalis. The other white-flowered species either have only simple (and sometimes forked) hairs (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 in diameter) with no or little secondary branching, whereas D. nivalis has minute hairs (< 0.2 mm) with abundant secondary branching. 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, whereas D. glabella usually has glabrous or subglabrous inflorescence branches, sepals and fruits, or more rarely fruits with scattered, simple hairs. These three species are therefore easily distinguished from all other species of Draba in Svalbard and from each other, both in flower and in fruit stages.

Habitat

Occupies poorly vegetated sites such as rocky outcrops, crevices and rock ledges, gravelly slopes, ridges, and more rarely in more densely vegetated heaths. On mixed substrates, always well drained with acidic to circumneutral soil reaction (pH), as opposite to D. fladnizensis which grows in similar sites but is absent from acidic substrates. Most common in exposed sites, with poor protection from snow during winter, and a longer growth season. Probably little grazed by reindeer and geese.

Distribution

Distributed in all zones and not rare in the polar desert zone on Spitsbergen and Nordaustlandet. Found in all sections. The species is recorded from Spitsbergen, Nordaustlandet and Prins Karls Forland.

The general range is circumpolar and arctic–alpine, reaching from the northern arctic zones far south in the mountains of W North America and C and E Asia but in Europe only south to S Norway.

Comments

The variation in pubescence in Draba nivalis is large and easily observed but perhaps not genetically very significant. Besides the common plants with an even, dense pubescence on leaves and stems, there are plants with marginal hairs only (‘subglabrous’), and also (but not yet found in Svalbard) completely glabrous plants with the same genetic markers as D. nivalis (Grundt et al. 2004; Elven et al. 2011). The differences in degree of pubescence are obviously inherited as the deviating plants are found as populations, sometimes exclusive for smaller regions (e.g., ‘subglabrous’ plants in parts of Varangerhalvøya, NE Norway). No genetic differences have yet been found among these pubescent, ‘subglabrous’, and glabrous plants, and there is no geographic pattern in the variation. We have therefore not assigned any taxonomic rank to the pubescence variants.

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.

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

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

Grundt, H.H., Kjølner, S., Borgen, L., Rieseberg, L.H. & Brochmann, C. 2006. High biological species diversity in the arctic flora. – Proceedings of the National Academy of Sciences 103: 972–975.

Grundt, H.H., Popp, M., Brochmann, C. & Oxelman, B. 2004. Polyploid origins in a circumpolar complex in Draba (Brassicaceae) inferred from cloned nuclear DNA sequences and fingerprints. – Molecular and Phylogenetic Evolution 32: 695–710.