Solitary herb growing in dense, often quite large, dense or more loose tussocks (diameter often 10 cm or more), often in large stands with near confluence of tussocks. Old leaves persist for 1—2 years. Each tussock has one central root and an extensively branched caudex. Aerial shoots relatively short but occasionally up to 5—7 cm with 3—5(9) pairs of leaves. Stems pubescent with very short (less than 0.05 mm), thick, down-pointing (retrorse), white hairs. Flowering stems usually short, rarely more than 2 cm, and the entire tussocks thereby being quite flat. The tussocks are often difficult to see when not in flower, merging with the gravel where they are growing.
Leaves opposite, 2—5 × 1—1.5 mm, spathulate with broad (winged) bases, ciliate in the lower 1/2—1/3 of margin (cf. the scientific name ‘ciliata’), otherwise glabrous, with more or less distinct mid vein and lateral veins, obtuse, green or reddish.
Flowers singly at end of flowering shoots (rarely up to 4 in a short dichasial cyme), abundant, often covering the entire tussock, with a distinct vanilla smell.
Flowers on pedicels up to 10 mm, radially symmetric, up to 10—12 mm in diameter, with 5 free sepals and petals. Sepals 3—5 × 1.2—1.7 mm, ovate, acute, with distinct mid vein and 2 lateral veins, glabrous or with a few short and thick, white hairs at the very base, purplish or sometimes green, with white or pink hyaline margins ca. 0.3 mm broad. Petals 5—6 × 2.5—3 mm, nearly twice as long as sepals, broadly elliptic, obtuse, strongly spreading, translucent white. Stamens 10; filaments 2—3 mm; anthers very small and short, ca. 3 mm. Gynoecium of 3 carpels with 3 stigma.
Fruit a capsule 4—5 mm, slightly longer than sepals, pear-shaped (pyriform) and opening by 6 teeth, slightly glossy, pale brown, with one room and several seeds.
Sexual reproduction by seeds; no vegetative reproduction. The distinct vanilla smell speaks for insect pollination and the plants are frequently visited by flies. Seed production is abundant in Svalbard and the seeds germinate to 30 % (Alsos et al. 2013).
There are no adaptations to any special kind of seed dispersal. We assume the dispersal to be passive. The only possible mode of long distance dispersal is within the digestive channel of birds.
Arenaria differs from other small Caryophyllaceae by having shorter and broader leaves and short, thick hairs on stems. The two species of Arenaria are rather different. Arenaria pseudofrigida is densely caespitose and has comparatively large flowers 10—12 mm in diameter; A. humifusa is rhizomatous and normally with scattered aerial shoots (but sometimes in small tussocks), and has small flowers 6—8 mm in diameter.
Arenaria pseudofrigida is a specialist on gravelly ground, often on dry, flat and exposed bars or terraces, either along the coast or on small elevations in valleys. It is very tolerant to drought and wind abrasion (the low tussocks may function as a protective layer keeping the fine grained soil from being blown away) but intolerant to competition. It is assumed to be calciphilous but is also found on the circumneutral sandstones near Longyearbyen. It has, however, not been found in any area with mainly acidic substrates.
The range is within the middle and northern tundra zones and the clearly continental to transitional sections, e.g., fairly wide. In Spitsbergen it is rather frequent along the middle and inner parts of Isfjorden, Kongsfjorden, Liefdefjorden (Bockfjorden), and Wijdefjorden. Single records are known from the north side of Bellsund, Prins Karls Forland and Edgeøya.
The global range is arctic amphi-Atlantic, restricted to NE Greenland, Svalbard, NE Fennoscandia, and N European Russia.
Arenaria pseudofrigida is part of a small European species group, the A. ciliata L. aggregate, with several species on open, usually calcareous ground in lowlands and mountains. Arenaria pseudofrigida is the single arctic outpost of this group.
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.