Solitary graminoid herb forming tussock by a densely branched rhizome. Rhizome branch lengths 0–0.5 cm. Culms (0.5)1–2(4) cm, shorter than the leaves during and after flowering, ascending or more rarely erect, slightly scabrous (strong lens).
Leaves 1–3 cm long, 0.5–0.8 mm broad at the base, narrowing into an acute apex, folded, scabrous along the leaf margins and on the mid vein, bright green with reddish withered leaves and leaf tips.
The flower in Carex is unisexual (either male or female), without perianth, and supported by a scale (the bract of the single flower). The male flower consists of 3 stamens. The female flower consists of a gynoecium of 2 or 3 fused carpels, with a single style and 2 or 3 stigmas, and with a single seed. The gynoecium is surrounded by a perigynium, a container with a narrow apical opening through which the style and stigmas emerge. The perigynia (and nuts) are either lenticular (when two carpels/stigmas) or trigonous (when three). The inflorescences are spikes, one or more per culm. If two or more spikes, all except for the uppermost are supported by more or less leaf-like bracts. Spikes may be unisexual or bisexual, and bisexual spikes may have the female flowers at base (basigynous) or at top (acrogynous). Flowers are wind pollinated and usually cross pollinated because the male flowers reach anthesis before the female flowers (protandry). Cross pollination predominates among sedges investigated in alpine Norway (Berggren & Haugset unpubl.), either due to the protandry or to genetic incompatibility. Seeds are spread inside their perigynia.
Inflorescence of one terminal spike 0.4–0.5 × 0.2–0.3 mm, bisexual with mainly female flowers and only a few male flowers at the base (i.e., acrogynous), ovate. Scales 1.2 × 2.2 mm, obovate and obtuse, brown with a narrow hyaline margin and a not very conspicuous lighter brown mid vein. Perigynia 1.5–2.0 × 1.2–1.3 mm, ovate, no beak, smooth, with enlarged cells, greenish first but later light brown when ripe. Stigmas 2.
Flat or lenticular nut within the perigynium.
Sexual reproduction by seeds; no vegetative reproduction. However, tussock may sustain for long periods by local vegetative growth. Flowering and seed-set is very regular. Seeds germinate to 62 % in an experiment (Alsos et al. 2013), an unusually high level of germination for a Carex.
The perigynia have enlargened cells that may be an adaptation to floating, and we assume that the main mode of dispersal is by sea currents.
There are only two Carex species in Svalbard which has the combination of cushion form and only one bisexual spike; Carex nardina and C. ursina. Both have rather narrow leaves, but those of C. nardina are narrower, usually curved and more pressed to the ground. Whereas the leaves of C. nardina are intravaginal, C. ursina has short runners. The spikes of C. nardina usually emerge above the leaves and are brown, those of C. ursina are situated among the leaves and are variegated in pale green and black.
On fine-grained substrates on seashore (i.e., salt marshes) and on circumneutral fine-grained substrates along rivers and streams close to the sea.
Common to scattered in the middle and northern arctic tundra zones; one site only in the polar desert zone. Found in the clearly continental to weakly oceanic sections. In Spitsbergen rather common on shores and along rivers in the inner fjord zone from Van Keulenfjorden and Van Mijenfjorden northwards. Also found in one locality on Edgeøya.
Carex ursina has a circumpolar range restricted to the arctic zones and occurs as frequent in the southern and middle arctic tundra zones, scattered in the shrub tundra zone and rare in northern arctic tundra zone.
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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.
