Solitary herb with basal caudex densely covered by leaf remains, densely branched into one or several clustered rosettes forming small to moderate-sized, dense tussocks. Each rosette potentially with one flowering scape (without leaves). Scapes erect, moderately elongating during and after flowering to 8–15 cm, densely pubescent with simple, forked, and few-rayed multibranched hairs up to 1 mm or more.
Leaf rosettes up to 6 cm. Leaves alternate, to 20 × 7 mm, entire, oblanceolate or obovate, acute, mid vein often prominent, green. Upper leaf surface with a moderate to dense pubescence dominated by stout, up to 1.2 mm long, simple and/or forked hairs, and with lower density of much smaller multibranched hairs (up to 0.6 mm); lower leaf surface moderately pubescent with 3–5-rayed cruciform or multibranched hairs; margin with stout simple hairs up to 1.3 mm.
Inflorescence a corymbose raceme with 4–9(12) flowers, rarely more, very short in flowering stage and not elongating much in fruiting stage. Pedicels 3–7 mm, stout, attached to scape at an angle of 50–80°, straight or moderately curved, with predominance of simple and forked hairs.
Flower radially symmetric with 4 free sepals and petals. Sepals up to 3 × 2.5 mm (i.e., nearly as broad as long), broadly ovate, greyish green without any pink or purple tinge, with broad white margins. Petals up to 7 × 6 mm (i.e., nearly as broad as long), contiguous or overlapping, patent (making the flower fully open), broadly obovate, notched, bright yellow.
Fruit a silicule up to 12 × 6 mm, erectopatent, oblong or ovate to nearly orbicular, pubescent with short stiff, mostly simple hairs, greyish green. Style long, ca. 1 mm or longer. Seeds 6–12 in each room, medium brown, up to 1.3 × 0.9 mm.
Sexual reproduction by seeds; no vegetative reproduction. Flowers are adapted to pollination by insects but the species is probably a mixed mater. Flowering and seed-set is regular and abundant in most years; mature seeds are regularly observed. Germinating from seed bank (Cooper et al. 2004).
There are no special adaptations to seed dispersal.
See also Draba alpina. Draba corymbosa is distinguished from all other yellow-flowered Drabas by the predominance of long, stout, simple hairs on leaves, making the plant visibly hirsute or strigose, by longer styles (often up to 1 mm or more), and by fruits with abundant, strigose hairs. The petals are also often larger and broader in D. corymbosa than in the others and their colour more bright sulphur yellow.
Growing mostly on dry ridges and heaths but also in bird cliff meadows, on dry parts of river bars and in disturbed sites. On dry or very dry substrates of mixed soil texture with good drainage, often at moderately exposed sites with thin snow pack during winter and longer growth season. Only on substrates with a circumneutral or basic soil reaction (pH); probably little grazed by reindeers and geese.
Present and often frequent in all zones and sections. Found on all the major islands in the Spitsbergen group (Spitsbergen, Nordaustlandet, Barentsøya, Edgeøya) and even on the harshest island in all of Svalbard, Kvitøya. Not reported from Bjørnøya.
The general range is circumpolar in the arctic zones, only very rarely penetrating south to mountains in the boreal zones.
Draba corymbosa is a highly polyploid (14–18×, 2n = ca. 100–144) and polymorphic species to which several different names have been applied in different regions (see Elven et al. 2011 for discussion of names): D. bellii in Greenland and Canada (type from Greenland), D. macrocarpa in Russia (type from N Siberia), and partly D. kjellmanii in European Russia and Svalbard (type from Novaya Zemlya). Also the names D. barbata (described from Siberia and North America, type from Siberia) and D. pohlei (described from Siberia) probably belong to this species. The name D. corymbosa has proved to be the oldest valid name in this group and its Canadian type (se Mulligan 1974) assigns the name unambiguously to the species in question.
Brochmann et al. (1992) have shown that D. corymbosa is heterogeneous in the true, genetic meaning of the concept and probably has arisen numerous times by different combinations of genomes from several species at lower ploidy levels. This study was based on plants from Svalbard only. When the entire circumpolar range is included, the heterogeneity and polymorphy will probably be even more pronounced. It is therefore not surprising that the species has been described under many different names. The crucial question is whether it is one species or a number or interrelated species. At present, we treat it as a single species with a very reticulate origin from more low-ploid parents. The reticulation may make it impossible to recognize and justify several species.
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.
Cooper, E.J., Alsos, I.G., Hagen, D., Smith, F.M., Coulson, S.J. & Hodkinson, I.D. 2004. Recruitment in the Arctic: diversity and importance of the seed bank. – Journal of Vegetation Science 15: 115–124.
Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF) Vascular plants. http://panarcticflora.org/
Mulligan, G.A. 1974. Confusion in the names of three Draba species of the Arctic: D. adamsii, D. oblongata, and D. corymbosa. – Canadian Journal of Botany 52: 791–793.