Solitary herb forming cushions up to 2 m in diameter and up to 20 cm tall. Tap root. Stem at ground level (caudex) richly branched. Dead leaves persist for several years, protecting the caudex branches.
Leaves opposite, densely crowded, 4–10(12) × 0.8–1.2(1.3) mm, linear, acute, ciliate with stout, triangular hairs or setae.
Flowers singly in shoot apices.
Flowers radially symmetric with 5 sepals and petals, bisexual or female. Calyx 1.5–2 × 1.5–2 mm, of fused sepals with short, obtuse and notched lobes. Petals free, 4–8 × 1.5–2.5 mm, erect up to half length, thereafter bending 90° outwards, apex slightly notched, pink (occasionally white). Stamens usually 10. Gynoecium of three carpels with three stigma, with one room.
Fruit a capsule that opens apically with six teeth. Numerous small seeds.
Sexual reproduction by seeds; no vegetative reproduction. Old stems may root but this is probably not sufficient to sustain independent individuals. Outcrossing and pollinated by insects. Produces a large number of ripe seeds. Germination 40–95 % at 20°C and around 20 % when germinated in field (Alsos et al. 2013; Müller et al. 2011).
No special adaptations to seed dispersal, although the apical opening of the capsule may ensure that seeds are spread only when the wind speed is over a certain level.
This is the only pink flowered species of the Caryophyllaceae in Svalbard. Non-flowering individuals may be recognized by the dense cushions and the opposite, densely crowded, linear leaves.
Most common in moderately to densely vegetated heaths and moderate snowbeds. On moderately well drained, mixed or fine textured substrates with acidic to basic soil reaction (pH). Requires moderate to good snow protection during winter. Probably little grazed by reindeer and geese.
Absent from the harshest parts of Svalbard. Frequent in the middle and northern arctic tundra zones, very rare in the polar desert zone. Occurs in all sections. Common on Spitsbergen and Bjørnøya, with a few records from Prins Karls Forland, Edgeøya and Nordaustlandet.
The general range reaches from Beringia eastwards across Canada, Greenland and N Europe to NW Siberia (i.e., with a huge gap in Asia), in the arctic zones and temperate mountains.
Silene acaulis is a remarkably distinct species in an arctic context, not closely related to any other arctic species. Its relatives are found in the southern temperate mountains from Europe to C Asia. However, there is some variation in the arctic material, associated with a large gap of about 100° longitude in N Siberia between the broadly amphi-Atlantic and the broadly amphi-Beringian parts of the range. Beringian and Cordilleran plants differ from the amphi-Atlantic ones in several features in leaves and flowers, summarized by Morton (2005). These Beringian–Cordilleran plants have been proposed as a separate race, ssp. subacaulescens (F.N.Williams) Hultén. Molecular evidence so far does not clearly support two taxa but we accept them (provisionally), even if there may be a transitional zone in North America. The Svalbard plant is accordingly ssp. acaulis.
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.
McCarthy, D.P. 1992. Dating with cushion plants: establishment of a Silene acaulis growth curve in the Canadian Rockies. – Arctic, Antarctic and Alpine Research 24: 50–55.
Morton, J.K. 2005. Silene Linnaeus. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico. 5. Magnoliophyta: Caryophyllidae, part 2: 166–214.
Müller, E., Cooper, E.J. & Alsos, I.G. 2011. Germinability of arctic plants is high in perceived optimal conditions but low in the field. – Botany 89: 337–348.