Life span

Perennial, probably fairly short-lived.

Growth form

Solitary herb with basal caudex sparsely covered by marcescent leaf remains, single or branching into a few or several clustered rosettes forming small, dense tussocks. Each rosette potentially with one flowering stem without leaves (scape). Flowering stems erect, very short in early flower stage, 1–3 cm or less, elongating strongly during and after flowering to 7–14 cm in the tundra zones but often remaining stunted in the polar desert zone, moderately pubescent with long-stalked cruciform hairs, at base also with some simple and forked hairs.

Leaf

Leaf rosettes small, up to 3 cm (rarely much broader). Leaves alternate, to 10 × 5 mm (rarely larger), greyish green, obovate or oblong, apex rounded, entire, mid vein not prominent, greyish green. Upper leaf surface moderately to densely pubescent with coarse, long-stalked, cruciform hairs up to 0.8 mm broad, more rarely with some forked and/or simple hairs up to 1 mm; lower leaf surface with similar hairs; proximal parts of margins with stout simple hairs up to 1.5 mm, distal parts predominantly with long-stalked cruciform hairs up to 1 mm.

Inflorescence

Inflorescence a raceme, very short in the flower stage but elongating in the fruit stage up to 4–5 cm (in the tundra zones, shorter in the polar desert), often with a zig-zag mid axis, may remain corymbose or even capitate in the polar desert, with 4–5(9) flowers. Pedicels ca. 2–5 mm, about as long as fruit, stout, attached with scape at an angle of 40–45º but regularly curved upwards, with predominance of long-stalked cruciform hairs more or less mixed with irregularly branched, forked and simple hairs.

Flower

Flowers radially symmetric with 4 free sepals and petals. Sepals up to 1.8 × 1.0 mm (i.e., nearly two times as long as broad), elliptic, oblong or ovate, greyish green, often tinged with red or purple and with a distinct, white margin. Petals very small and narrow, 1.5–2.0 x 0.5–0.7 mm, not contiguous or overlapping, erectopatent (making the flower half-open), narrowly spathulate or cuneate, deeply notched, pale yellow.

Fruit

Fruit a silicule up to 8 × 3.5 mm, suberect or erectopatent, oblong, rounded towards both base and apex, sparsely or densely pubescent with short (up to 0.4 mm) forked and simple hairs, greyish green. Style very short, ca 0.1 mm, and the stigma seems to be sessile. Seeds 6–9 in each room, medium brown, up to 1.0 × 0.9 mm.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. Flowers are not adapted to pollination by insects and are probably predominantly or exclusively self pollinating. 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

Draba micropetala + D. pauciflora differ from the other yellow-flowered species, when in flower, by their very small and narrow petals, when in fruit, by their very short styles (ca 0.1 mm), and always by rounded to obtuse leaves with very coarse, long-stalked, cruciform hairs (in addition to other hairs). Draba alpina + D. oxycarpa differ from the others in absence of coarse, stout hairs on leaves (and fruits) and in the other characters mentioned above. Draba corymbosa differs from all the others in predominance of long, stout, simple hairs on leaves, making the plant visibly hirsute or strigose, in longer styles (often 0.2 mm or more), and in fruits with abundant, strigose hairs. The petals are also often larger and broader in D. corymbosa than in the others.

Draba micropetala and D. pauciflora are consistently different in several features: In D. micropetala with leaves with predominance of cruciform hairs (especially in apex), leaf apex rounded, fruits ovate–oblong, strigose and greyish green, and inflorescence elongating in fruit with a zig-zag mid axis; in D. pauciflora with leaves with predominance of simple and forked hairs, leaf apex obtuse, fruits obovate and pear-shaped, sparsely pubescent and olive green, and inflorescence not elongating (but the scapes elongate in both species). With careful study, they are not mistaken for each other or for any other Draba in Svalbard.

Habitat

Most frequent on open ground or in heaths and early snow-beds with short-grown vegetation, often a sparse moss carpet, but also on solifluction terraces, patterned ground, and gravel plains. Avoids very moist and wet sites and deep moss carpets, where it is replaced by Draba pauciflora. Usually on fine textured substrates within a wide range of soil reaction (pH) from quite acidic to basic. Probably little grazed by reindeer and geese.

Distribution

Cryophilous. Present in all zones and sections. One of the most hardy of vascular plants in Svalbard and slightly less common in the middle arctic tundra zone than in the harsher zones. Recorded from all major islands in the Spitsbergen group (Spitsbergen, Prins Karls Forland, Nordaustlandet, Barentsøya, Edgeøya) and also from some harsh, off-lying islands like Hopen and Kong Karls Land. Not recorded from Bjørnøya.

The general range is interrupted circumpolar in the northern arctic zones. In Europe, it is restricted to Svalbard.

Comments

Draba micropetala belongs to an exclusively arctic group with three known species: the circumpolar D. micropetala and D. pauciflora and the Canadian D. simmonsii Elven & Al-Shehbaz (Elven & Al-Shehbaz 2008). Draba micropetala and D. pauciflora have lower chromosome numbers than the other yellow-flowered species on Svalbard (the ploidy level of D. simmonsii is not known). The hexaploid (2n = 48) D. micropetala is consistently different from the tetraploid (2n = 32) D. pauciflora, in Svalbard and elsewhere, and is not very variable.

Until the 1980s, and even later, the name usually applied for this species, in Svalbard and elsewhere, was D. oblongata R.Br. ex DC. (see, e.g., Rønning 1964, 1979; Tolmachev 1975). However, Mulligan (1974) made clear that the name D. oblongata belongs to an entirely different, white-flowered species (previously named D. groenlandica E.Ekman) and connected the name D. micropetala to the yellow-flowered plant by locating a Canadian holotype. Other authors have applied the name D. adamsii, based on a Russian type. The name Draba adamsii is a younger name for D. pauciflora but has been misapplied, both in Svalbard and in, e.g., Greenland, for D. micropetala or as a collective name for D. micropetala + D. pauciflora (e.g., Böcher et al. 1978). The correct usage of names for the two Svalbard plants was established by Elven & Elvebakk (1996).

Brochmann et al. (1992, 1993) showed that the differences in chromosome numbers previously reported for the yellow-flowered Drabas were followed by differences in molecular markers supporting several distinct species. Draba micropetala and D. pauciflora may be less closely related to the species with larger flowers (D. alpina, D. corymbosa, D. oxycarpa) than previously assumed, see Elven et al. (2011).

Literature

Böcher, T.W., Fredskild, B., Holmen, K. & Jakobsen, K. 1978. Grønlands flora. Ed. 3. – P. Haase & Søns Forlag, København.

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. & Al-Shehbaz, I.A. 2008. Draba simmonsii (Brassicaceae), a new species of the D. micropetala complex from the Canadian Arctic Archipelago. – Novon 18: 325–329.

Elven, R. & Elvebakk, A. 1996. Part 1. Vascular plants. – In: Elvebakk, A. & Prestrud, P. (eds.), A catalogue of Svalbard plants, fungi, algae, and cyanobacteria. – Norsk Polarinstitutts Skrifter 198: 9–55.

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

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.

Rønning, O.I. 1964. Svalbards flora. – Norsk Polarinstitutt, Oslo.

Rønning, O.I. 1979. Svalbards flora. Ed. 2. – Norsk Polarinstitutt, Oslo.

Tolmachev, A.I. 1975. Draba L. – In: Tolmachev, A.I. (ed.), Flora Arctica URSS. VII. Papaveraceae–Cruciferae: 106–155.