Perennial, moderately long-lived.
Solitary herb with a tap root and a short unbranched or branched caudex with leaf remains from previous years, when branched forming dense tussocks up to 5?10 cm in diameter. Caudex branches ending in leaf rosettes without or with spreading or erect flowering scapes (stems without leaves). Scapes very short in flowering stage (flowers often situated in the middle of basal leaf rosettes), elongating in late flowering and fruit stage to 6(8) cm, moderately densely pubescent with ca. 1 mm long, simple, flattened, white hairs.
Leaves alternate, 10?25(30) × 2?4(5) mm, narrowly oblanceolate or spathulate, obtuse, entire or with 1?2 obscure teeth on each side, glabrous or very sparsely pubescent with simple or few-branched hairs, dark green, often tinged with purple.
Inflorescence a very short raceme in flowering stage, 0.5?1 × 0.8?1.2 cm, elongating strongly in fruiting stage to 2?3(5) cm, with 8?15 flowers. Pedicels stout, attached at an angle of 70?90°, 2?4 mm long (fruiting stage), shorter than fruit. Inflorescence mid axis and pedicels with same type of hairs as the stem.
Flowers radially symmetric, 3?5 mm in diameter, with 4 free sepals and petals. Sepals 2.0?2.8 × 1.8?2.3 mm, suborbicular, rounded at apex, purple with very narrow, pale purple margin. Petals 2?3 × 0.8?1.2 mm, spathulate with short claw, rounded at apex, contiguous or slightly overlapping, white or often purplish at base, often turning purple with age (‘purpurascens’). Stamens 6; filaments ca. 3 mm, flattened at base; anthers 0.3?0.4 mm, almost orbicular. Gynoecium of 2 carpels with 2 rooms separated by a secondary, hyaline wall. Stigma slightly bifid.
Fruit a siliqua with two rooms, opening as the two side walls (valves) fall off, leaving the seeds attached to the suture or frame (replum) between the valves. Fruit 6?10 × 2.5?4 mm, thick, sausage-shaped and turgid, with valves pubescent with flattened, white hairs. Style thick, ca. 1 mm long. Seeds in 2 rows in each room (6?10 seeds per room), 1.0?1.2 × 0.7?0.9 mm, brown.
Sexual reproduction by seeds; no vegetative reproduction. Flowers are adapted to pollination by insects but we assume that self pollination prevails. Seed maturation is regular. Seeds germinated to 60 % in an experiment (Alsos et al. 2013).
Seeds are not adapted to any special way of dispersal, probably mostly passively dispersed locally.
Braya glabella ssp. purpurascens can be mistaken for Cardamine bellidifolia, Cochlearia groenlandica, white-flowered Draba spp., and Eutrema edwardsii. It differs from Cardamine bellidifolia, Cochlearia groenlandica and Eutrema edwardsii in pubescent leaves (partly), stems and fruits. From Draba it differs in the shape of fruits, sausage-shaped and parallel-sided, and also in the flattened hairs. The fruits of Draba are oblong or ovate with curved sides and have no flattened hairs.
On ground open or only slightly covered by algal crust, in moist site types. Usually on soil patches in frost patterned ground, on sediment or gravel plains, or on dry patches in shallow mires, sometimes on moist calcareous gravel. Braya is a specialist of calcareous ground with little competition, sometimes very common in areas with pure limestone.
Braya glabella ssp. purpurascens occurs in all zones except the polar desert and all sections except the weakly oceanic. On Spitsbergen it occurs from Sørkapp Land in the south to the north coast but with its main concentrations in the large fjord systems: Van Keulenfjorden, Van Mijenfjorden, Isfjorden, Kongsfjorden, Liefdefjorden, Woodfjorden, and Wijdefjorden. In addition, it is reported from one site on NW Edgeøya and two on Nordaustlandet.
The global distribution is arctic circumpolar, most common in the western parts (Greenland, North America), and probably extending south in the N Rockies in W North America (as B. henryae Raup). In Europe, its southernmost occurrences are found near North Cape on the island Magerøya in Finnmark in N Norway.
The Braya of Svalbard is uniform and all plants are assigned to B. glabella ssp. purpurascens (B. purpurascens), even if there is some not yet studied variation in fruit pubescence and shape. The relegation to subspecific rank is rather recent (Harris 1985; Rollins 1993; Cody 1994; Warwick et al. 2003). We are familiar both with the more W North American B. glabella s. str. and with the arctic B. purpurascens and are not convinced that this merger within one species is justified. However, we here follow the current established usage and assign it as a subspecies.
There is an intriguing corollary due to the politics of species conservation. This is an extremely rare and threatened species in mainland Norway, only known from a few small populations on a dolomite plateau on the island Magerøya. These are the only populations on the European mainland, and Norway had to give it strict protection to be able to sign the Berne agreement on threatened species. Nevertheless, P. glabella ssp. purpurascens is still under decimation and critically threatened by intense grazing of domesticated reindeer at its only occurrence on the European mainland. As Svalbard is part of Norway as concerns nature management and conservation, this rather common species in Svalbard is at present given a stricter protection than tens of much more threatened species in the archipelago. Hence, every development project (e.g., mining) in parts of Svalbard with limestone will be in conflict with Norway's signature of the Berne protocol.
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.
Cody, W.J. 1994. Nomenclatural changes and new taxa for the Yukon flora. – Canadian Field-Naturalist 108: 93–95.
Harris, J.G. 1985. A revision of the genus Braya (Cruciferae) in North America. – Ph.D. Thesis, Univ. Alberta, Edmonton.
Rollins, R.C. 1993. The Cruciferae of Continental North America. – Stanford Univ. Press, Stanford.
Warwick, S.I., Al-Shehbaz, I.A., Sauder, C.A., Harris, J.G. & Koch, M. 2003. Phylogeny of Braya and Neotorularia (Brassicaceae) based on nuclear ribosomal internal transcribed spacer and chloroplast trnL intron sequences. – Canadian Journal of Botany 82: 376–392.