- Name also: Beautiful Sandwort, Red Sadwort, Arctic Sandwort, Boreal Stitchwort
- Family: Pink Family – Caryophyllaceae
- Growing form: Perennial tufted herb.
- Height: 3–8cm (1.2–3.2 in.). Stems quite erect, sparsely branched, at least top (often completely) sparsely haired.
- Flower: Corolla regular (actinomorphic), white–reddish, approx. 1 cm (0.4 in.) wide. Petals 5, ovate–obovate, entire, approx. 3 mm (0.12 in.) long, shorter than sepals. Sepals 5, tapered, 3-veined. Stamens 10. Pistil of 3 fused carpels, styles 3. Flowers stalked. Buds long.
- Leaves: Opposite, stalkless, greyish green. Blade linear–lanceolate, 4–8 mm (0.16–0.32 in.) long, with entire margins, 3–5-veined.
- Fruit: Narrow, green, 3-valved, 5–6 mm (0.2–0.24 in.) long capsule.
- Habitat: Snow-bed sites in fell tundra, rocks, gravels, precipices. Requires alkaline soil (is calcicole).
- Flowering time: July–August.
- Endangerment: Vulnerable.
Mountain sandwort is very rare species growing on the large fells of Enontekiö on gravels and rocky outcrops on the high fells of Saana, Malla and Kuottuskaiti. It is low-growing and densely tufted with glandular hairs and a reddish stem (the scientific name is rubella means ‘somewhat red’). The sepals of its flowers are tapered and the petals, which are shorter than the calyx, are broadly ovate or obovate.
Apart from mountain sandwort, two other sandworts that grow on the Finnish tundra are tufted sandwort (M. biflora) and teesdale sandwort (rock sandwort, bog sandwort, M. stricta). These small, tufted plants are quite similar to each other. Of the two, tufted sandwort makes wider but rarer tussocks. Its stem has fine and glandular hairs, its sepals are blunt and its petals, which are longer than the calyx, are narrowly long. Densely tufted teesdale sandwort’s stem is quite glabrous and has relatively and noticeably long flower stems which terminate in small flowers with narrowly long petals. Teesdale sandwort grows very rarely on rocky outcrops and gravel slopes on the tundra on the large fells of Enontekiö. There are stands at least on Saana, Malla and Toskalharji. Tufted sandwort is slightly more widespread: it is found quite commonly on the large fells of Enontekiöa and also rarely in Inari and the Central Lapland forest belt and northern parts of Koillismaa.
Snow pearlwort (Sagina nivalis) and Alpine pearlwort (Arctic pearlwort, S. saginoides) are two other small, tufted close relatives that grow in Lapland too. The easiest way to tell them apart is in the fruiting stage: their capsules are 4–5 valved while the sandworts are 3-valved. Atctic sandwort (Norwegian sandwort, Arenaria norvegica) and fringed sandwort (A. pseudofrigida) are also small-flowered close northern relatives, although they are adorned extravagantly in relation to their size with large white flowers. Both are very rare in the wild in Finland.