Life span

Perennial, moderately long-lived.

Growth form

Solitary herb with basal caudex sparsely covered by marcescent leaf remains, single or branching into several clustered rosettes and forming small, loose tussocks. Each rosette potentially with one flowering stem without leaves (scape). Flowering stems erect, more rarely ascending, moderately elongating during and after the flower stage to 10 cm or more, sparsely to densely pubescent with irregularly few-branched hairs and slender simple hairs.

Leaf

Leaf rosettes up to 3 cm or more. Leaves alternate, up to 15 × 5 mm, elliptic, narrowly obovate or oblanceolate, acute, entire, mid vein not or moderately prominent, green. Upper leaf surface glabrous or sparsely to densely pubescent with simple hairs (up to 1.2 mm), forked, and more rarely cruciform and irregularly branched hairs; lower leaf surface moderately pubescent with same hair types; margins mainly with stout simple hairs up to 1.2 mm.

Inflorescence

Inflorescence a raceme, mostly with 2–5 flowers but sometimes up to 10, very short in flower stage, not elongating much in fruit stage. Pedicels 2–4 mm, shorter than fruit and sometimes less than half of fruit length, stout, attached with scape at an angle of 50–80°, with predominance of simple hairs, sometimes only such ones.

Flower

Flowers radially symmetric with 4 free sepals and petals. Sepals up to 2 × 1.5 mm (i.e., about 1.5 times as long as broad), broadly ovate or elliptic, pale greyish green, distally sometimes slightly tinged with pink or purple, with broad white margins. Petals up to 5 × 4 mm, contiguous or overlapping, patent (making the flower fully open), broadly obovate or spathulate, notched, pale or bright yellow.

Fruit

Fruit a silicule up to 9 × 5 mm, erect to erectopatent, ovate or rarely lanceolate, glabrous except for short stout hairs in the margin (along the suture between the valves), very rarely sparsely pubescent on valves, dark greyish green. Style short, up to 0.3 mm. Seeds 4–7(8) in each room, mainly in the distal part of the fruit, dark brown to nearly black, up to 1.4 × 1.1 mm.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. Flowers comparatively large and adapted to pollination by insects; probably a mixed mater. Flowering and seed-set is regular and abundant in most years; mature seeds are regularly observed.

There is no special adaptation to seed dispersal.

Comparison

See also D. alpina. The five yellow-flowered species of Draba found in Svalbard are often confused. They can be assigned to three groups: D. alpina + D. oxycarpa; D. corymbosa; and D. micropetala + D. pauciflora. Draba alpina + D. oxycarpa differs from the two other groups in absence of coarse, stout hairs on leaves (and fruits), from D. micropetala + D. pauciflora also in much larger petals and longer styles.

Draba alpina and D. oxycarpa are often difficult to keep apart. The most reliable diagnostic characters seem to be the following: In D. alpina petals are narrower and erectopatent (i.e., half open flowers), sepals are narrow, ca. 2 times as long as broad and purplish tinged, fruit stand is elongated, fruits glabrous or sparsely hairy also on valves, and seeds medium brown and slightly smaller (ca. 1.0 × 0.9 mm); in D. oxycarpa petals are broader and patent (i.e., fully open flowers), sepals are broader, 1–1.5 times as long as broad and not purplish tinged, fruit stand is subcorymbose, fruits mostly only hairy marginally, on the suture between the valves, and seeds blackish and larger (ca. 1.2 × 1.0 mm). A major character distinguishing D. oxycarpa from D. alpina in mainland Norway is the pale yellow petals of the former; in Svalbard both species usually have bright yellow petals.

Habitat

Most common in heaths among dwarf shrubs and other forbs, snowbeds with an early melt, bird cliff meadows, but also gravel plains and disturbed sites. On fine textured or mixed substrates, well drained to fresh, and from weakly acidic to basic soil reaction (pH). Probably absent from strongly acidic substrates. Usually with considerable to moderate snow protection during winter but less dependent upon it than its look-alike D. alpina. Probably little grazed by reindeer and geese.

Distribution

Present in all zones and sections but less common in the polar desert zone and the clearly continental section than in the others. Found on all the major islands in the Spitsbergen group (Spitsbergen, Prins Karls Forland, Nordaustlandet, Barentsøya, Edgeøya) and also on Bjørnøya.

Draba oxycarpa has an amphi-Atlantic range that includes E Greenland, Scandinavia (S and N), Svalbard, and N European Russia east to Polar Ural. It is possible that also the yellow-flowered Draba of Iceland and Jan Mayen belong to D. oxycarpa.

Comments

See also Draba alpina.

Draba oxycarpa is an octoploid, amphi-Atlantic species. A ‘parallell’ species, largely similar in morphology and also octoploid, is known from Wrangel Island, E Chukotka, and W Alaska, i.e., the central Beringian districts. It has provisionally been denoted as Draba ‘pseudo-oxycarpa’ (by Elven et al. 2011).

There is some morphological and ecological variation within D. oxycarpa but Brochmann et al. (1992) demonstrated close genetic connections between plants in S Scandinavia (Dovrefjell mts) and Svalbard, supporting only one species. Further, their studies indicated that D. oxycarpa is consistently different from its morphologically most similar relative in the Nordic regions: D. alpina. The plants of D. oxycarpa in S Scandinavia nearly always have broad, pale sepals and broad, patent, pale yellow petals, with a short, corymbose inflorescence in the fruit stage, and with distinctly ovate fruits distinguishing it from plants of D. alpina. They also grow on more well drained soil, in more exposed sites with less snow protection, and they start flowering weeks before D. alpina in the same areas. In the morphological characters mentioned, they differ markedly from D. alpina. However, plants of D. oxycarpa in N Scandinavia and in Svalbard usually have bright yellow petals and also differ from those of S Scandinavia in one or more other characters and often approach D. alpina, and they are also less strictly confined to well drained, exposed sites. The characters we have found most reliable as diagnostic throughout the major parts of the range of the species (Scandinavia, Iceland, Greenland, Svalbard) are seed colour followed by sepal and petal shape and marginal hairs on the fruits.

This species has been recognized in Svalbard since the late 1930’s but under the name D. gredinii E.Ekman (described in 1933 from Greenland as a new species). The name Draba oxycarpa Sommerf. (described in 1833 from Svalbard and perhaps the Dovrefjell mts as a new species) was re-introduced by Bretten (1973) as the priority name for this species, especially for plants in the Dovrefjell mts. Identity between the Svalbard plant (as D. gredinii) and the Scandinavian one (as D. oxycarpa) was argued for by, e.g., Bretten (1973), based on morphology, subsequently supported genetically and cytologically by Brochmann et al. (1992)

Draba oxycarpa is a mixed mater, probably mainly inbreeding, but perhaps more outcrossing than D. alpina due to more widely open and larger flowers (Brochmann & Elven 1992; Brochmann 1993). Together with the different ecology of D. oxycarpa in Svalbard compared with S Scandinavia, this may help explain a rather strange feature in hybridization. Even if extensive hybridization has been assumed among the species of Draba by previous authors (especially Elisabeth Ekman in the 1920's to 1940's), observers today are reluctant to accept as hybrids plants without signs of any abortion (and the “hybrids” of Ekman were almost always fully pollen and seed fertile). We rarely see plants with obvious abortion (fruits typically abort at an early stage in Draba and are retained on the dry scapes, often for several years). However, we see some, and the most common Draba hybrid in Svalbard is D. lactea × oxycarpa, seen with one or a few individuals nearly every year during our field works. This hybrid has never been observed in Scandinavia, even if the ranges of the two parents overlap also there (both in the north and in the south). The explanation of this discrepancy may be found in the differences in habitat (for both species) between Scandinavia and Svalbard, and an overlap in flowering times in Svalbard, but not in Scandinavia, but there may also be a genetic explanation.

Literature

Bretten, S. 1973. Slekta Draba i Knutshø-Finshøområdet på. Dovre. Sider ved dens systematikk og autøkologi. – Cand. real. Thesis, Univ. Trondheim, Trondheim.

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

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).