Solitary graminoid herb with a densely branched vertical rhizome, growing as dense tussocks mainly of intravaginal shoots. Numerous reddish to light brown basal sheaths. Culms (2)4–6(8), shorter than or as long as the leaves during and after flowering, slightly scabrous (strong lens). Leaves and culms sometimes curved in one direction and appressed to the ground, giving the impression of a well-used kitchen brush.

Leaves 5–8(10) cm long, 0.1–0.3 mm broad at the base, involute, narrow, narrowing into an acute apex, often sideways twisted in the rosettes when seen from above, with scabrous margins, dark green with withered 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 0.6–0.8(1.0) × 0.5–0.6 cm, ovate, bisexual with female flowers at the base (basigynous). Scales obovate, obtuse to acute, brown with pale brown mid vein and a more or less broad hyaline margin. Perigynia 3–5 × 1.5–2 mm, with a small foot (1 mm), obovate (broader above the middle when including the foot) or broadly elliptic, flat, brown, scabrous at margin from the middle and up to the whitish apex, with a 0.1–0.2 mm long bifid beak. Stigmas 2.

Lenticular nut within the perigynium.

Sexual reproduction by seeds; no vegetative reproduction. Tussocks may, however, sustain for long periods (hundreds of years?). Assumed ripe fruits did not germinate in an experiment (Alsos et al. 2013) but this may be due to general difficulties in germinating sedge fruits in laboratories. However, present distribution, structure of populations, and size of individuals suggest that the species regularly reproduces by seeds.

Fruits' (inside perigynia) have no special adaptation to dispersal but are generally easily dispersed by wind, water and birds, perigynia of C. nardina perhaps especially easily by wind as they grow on exposed ridges and as they are fairly flat and easily moved by wind.

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 towards the ground. While 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 exposed calcareous ridges with fine to medium fine substrate. Often alone on the ridges or associated with, e.g., Poa abbreviata and Potentilla pulchella.

Locally frequent in the middle arctic tundra zone, scattered in the northern arctic tundra zone and barely penetrating to the polar desert zone. In the transitional, weakly and clearly continental sections. Rather common in areas with calcareous soils in N Spitsbergen and in Nordaustlandet, one location on Prins Karls Forland but not found on other islands. Farther south, there is a single report from near Midterhuken in Bellsund (Nathorst Land).

Carex nardina s.l. has a disjunct distribution in Greenland and North America extending south to the Rocky Mts. and to Gaspé Peninsula in Quebec in E Canada. It is barely crossing the Bering Straits to Chukotka in the Russian Far East and the North Atlantic with a scattered range in Iceland and N Scandinavia. For the two proposed races, see Comments.

American (incl. Greenland) and Scandinavian plants of Carex nardina have in previous times often been assigned to two different species or subspecies: C. nardina s. str. (ssp. nardina) described from N Sweden, and C. hepburnii (C. nardina ssp. hepburnii) described from the Rocky Mts. in Canada (see, e.g., Egorova 1999). The Scandinavian plants are usually very stunted with curved leaves and culms; the American plants are more often much taller (up to 20 cm or more) with erect leaves and culms. However, these characters are strongly modificative, and recent American authors have generally not accepted ‘hepburnii’ (Murray 2002).

There is some variation within the species in growth form. Very narrow and curved leaves dominate in plants from Scandinavia (ssp. nardina), whereas slightly broader and more upright leaves dominate in plants from Svalbard, Greenland and North America (ssp. hepburnii), but this character is not consistent (based on material available at TROM, R. Elven & I.G. Alsos observ.). A potentially more useful character is the shape of perigynia. The perigynia are overall narrow in Scandinavian plants, broader and more obovate in plants from Svalbard, Greenland and Canada. There may also be some differences in the shape of the beak and in how scabrous it is. A series of measurements give for C. nardina ssp. hepburnii 3.0–5.0 × 1.5–2.0 mm, for ssp. nardina (3.0)3.5–5.0 × 1.4–1.6 mm. Scandinavian plants (ssp. nardina) have a more distinct beak, ca. 0.5 mm, and a distinct foot or stipe, 0.5—1 mm, whereas the plants from elsewhere (ssp. hepburnii) have an indistinct beak, ca. 0.4 mm, and an indistinct foot, ca. 0.2 mm. We provisionally accept two races (but not two species): ssp. nardina in Scandinavia and Iceland, ssp. hepburnii in Svalbard, Greenland, Canada, Alaska, and Chukotka.

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.

Egorova, T.V. 1999. The sedges (Carex L.) of Russia and adjacent states. – St.-Petersburg State Chemical–Pharmaceutical Academy, St.-Petersburg, and Missouri Bot. Gard. Press, St. Louis.

Murray, D.F. 2002. Carex Linnaeus sect. Nardinae (Tuckerman) Mackenzie in N. L. Britton et al., N. Amer. Fl. 18: 21. 1931. – In: Flora of North America Editorial Committee (eds.), Flora of North America North of Mexico 23. Magnoliophyta: Commelinidae (in part): Cyperaceae: 568–569.