Life span

Perennial, but probably not very long-lived.

Growth form

Solitary herb with basal caudex sparsely covered by marcescent leaf remains, single or branching into a few or several clustered rosettes and forming small, loose to 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 5–10 cm in the tundra zones but may remain stunted in the polar desert zone, moderately pubescent with simple, forked, and cruciform hairs.

Leaf

Leaf rosettes small, up to 3 cm (rarely much broader). Leaves alternate, to 10 × 4 mm (rarely larger), entire, obovate or oblanceolate, apex obtuse or subacute, rounded, mid vein moderately  prominent, greyish green. Upper leaf surface moderately pubescent with coarse simple hairs up to 1 mm, rarely glabrous; lower leaf surface with simple hairs of similar size and often with long-stalked cruciform hairs up to 0.5 mm; margins predominantly with stout, simple hairs up to 1.3 mm, sometimes mixed with forked hairs of similar size.

Inflorescence

Inflorescence a raceme with 2–6 flowers, very short in flower stage and not much elongating in fruit stage, especially not in the polar desert zone. Pedicels 1.5–4 mm, about as long as the fruit, moderately stout, attached with stem at an angle of 40–45° but regularly curved upwards, with predominance of simple or forked hairs.

Flower

Flowers radially symmetric with 4 free sepals and petals. Sepals up to 2.3 × 1.5 mm (i.e., less than two times as long as broad), ovate, greyish green, often tinged with red or purple and with distinct, white margins. Petals very small and narrow, 2–3 × 0.6–1.3 mm, narrowly spathulate or oblanceolate, deeply notched, not contiguous or overlapping, erectopatent (making the flower half-open), pale yellow.

Fruit

Fruit a silicule up to 10 × 5 mm, suberect, obovate, rounded towards apex, glabrous or sparsely pubescent with very short (up to 0.2 mm) simple hairs, olive green. Style very short, ca 0.1 mm, and the stigma appears sessile. Seeds 6–9 in each room, medium brown, up to 1.5 × 1 mm.

Reproduction

Sexual reproduction by seeds; no vegetative reproduction. Flowers not adapted to insect pollination; probably almost exclusively self pollinated. 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 of Draba in Svalbard, 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 two others in absence of coarse stout hairs on leaves (and fruits) and in characters mentioned above. Draba corymbosa differs from both the other groups 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 other species.

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

Usually growing in densely vegetated moist heaths and tundra, in seepage and on mires, solifluction terraces, moist patterned ground, snowbeds, moist polar desert, nearly always with a moss carpet. Associated with fine textured substrates within a wide range of soil reaction (pH) from quite acidic to basic. Growth sites are usually with good snow protection during winter, and the species is probably adapted to short growth season in snowbeds. 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, less frequent in the middle arctic tundra zone than in the harsher zones, and less frequent in the weakly oceanic and transitional sections than in the more continental others. Recorded from most major islands in the Spitsbergen group (Spitsbergen, Nordaustlandet, Barentsøya, Edgeøya) and also from some harsh, off-lying islands like Kong Karls Land and Kvitøya. Not recorded from Bjørnøya.

The general range is interrupted circumpolar in the northern arctic zones, only rarely reaching south to the arctic boundary.

Comments

Draba pauciflora belongs to an exclusively arctic group with three known species, the circumarctic D. micropetala and D. pauciflora, and the Canadian D. simmonsii Elven & Al-Shehbaz (see Elven & Al-Shehbaz 2008; Al-Shehbaz et al. 2010; Elven et al. 2011). The two former are at lower ploidy levels than the other yellow-flowered species (the ploidy level of D. simmonsii is not known). The tetraploid (2n = 36) D. pauciflora is consistently different from the hexaploid (2n = 48) D. micropetala in molecular markers (Brochmann et al. 1992) and morphology, but is probably more polymorphic than the latter.

The common plant of Draba pauciflora,in Svalbard and elsewhere, is a ‘morph’ that is relatively tall-grown in the fruit stage, with an elongated scape with fruits only in the uppermost part, and with very few, fairly large, obovate (pear-shaped), and olive green subglabrous fruits. This ‘morph’ is typical for the wet moss tundras and mires of the southern to northern arctic tundra zone, which is the main worldwide range of the species. In the polar desert zone and in high altitude locations in mountains, another ‘morph’ is found, with very stunted growth, scape not elongating, often more numerous and differently shaped fruits (elliptic or oblong), greyish green (not olive green), and distinctly hairy. We have seen this ‘morph’ also in material from Greenland and Canada. Whether the variation is just clinal along the latitudinal and altitudinal gradients, or taxonomic, is not known, but Svalbard would be a suitable place for studying the subject.

Rønning (1964, 1979) misapplied the name D. micropetala for D. pauciflora, and he misapplied the names D. oblongata (Rønning 1964) and D. adamsii (Rønning 1979) for D. micropetala, i.e., all names were misapplied from the first edition of Rønning's flora (1964) until Lid & Lid (1995) and Elven & Elvebakk (1996). Hence, all records of Draba pauciflora pre-1996, and especially those identified using Rønning's floras, must be confirmed or re-determined.

Literature

Al-Shehbaz, I.A., Windham, M.D. & Elven, R. 2010. Draba Linnaeus. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico. 7. Magnoliophyta: Salicaceae to Brassicaceae: 269–347.

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).

Lid, J. & Lid, D.T. 1995. Norsk flora. Ed. 6 by R. Elven. – Det Norske Samlaget, Oslo.

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

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