- Written also: Alpine Rock-cress
- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Perennial herb.
- Height: 10–30 cm (4–12 in.). Stem base commonly many-branched, spreadingly stellate-haired, greyish green (sometimes hairless, pale green). Loosely tufted, base with many flowerless rosettes.
- Flower: Corolla regular (actinomorphic), white, approx. 1 cm (0.4 in.) wide; petals 4, wide, 7–8 mm (0.28–0.32 in.) long. Sepals 4. Stamens 6, of which 4 long and 2 short. Gynoecium fused, a single carpel. Inflorescence a raceme, extending in fruiting stage.
- Leaves: In basal rosette and alternate on stem. Rosette leaves stalked, stem leaves stalkless, uppermost amplexicaul. Blade elliptic, with large, sharp teeth, stellate-haired, stem leaves with sagittate base.
- Fruit: Many-seeded siliqua, commonly curved, cylindrical, 2–3 cm (0.8–1.2 in.) long, spreading. Stalk 0.6–1.2 cm (0.25–0.5 in.) long, ascending oblique.
- Habitat: Fell tundra snow-bed sites, damp gravels, wet rock shelves, springs, stream banks, river banks. Also the forest belt.
- Flowering time: July–August.
Alpine rockcress likes the open tops of fells but also grows around water in the birch and conifer forest belts. As a fell plant it is common but sparse. The minimalist landscape of Enontekiö’s large fells has the most suitable places for the species to grow in, from Lappish rock faces that are kept damp by running water to rocky frostlands and snow-bed sites.
Alpine rockcress thrives on soil that has a little or a lot of nitrogen, but it avoids the poorest soils. The southernmost fell stands are on the wet mossy surfaces of Saariselkä’s stream-banks as the southernmost single fells lack the damp environments that the species has adapted to. It grows as a rare plant around springs as far as Kuusamo, in Nuukavaara in Pudasjärvi, and in the canyons of Koillismaa.
Alpine rockcress that grows in sheltered springs becomes large and luxuriant while the same species in stony nooks and crannies on open tundra looks much more modest. The properties of the fruit and flowers do not vary in the same way, however, so the identification markers generally hold true for all the plants. It can take years for alpine rockcress in harsh conditions in the north to make a stem and flower.
Alpine rockcress is sometimes cultivated in rock gardens and as ground cover by names Garden arabis, Mountain rock cress or Caucasian rockcres, sometimes it is sold as its Alpine rockcress’ subspecies, A. alpina ssp. caucasica, sometimes as an independent species, Arabis caucasica.