Solitary graminoid herb forming dense tussocks from an often richly branched caudex. Almost all leaves crowded at the end of caudex branches. Culms up to 3–5(10) cm, smooth but slightly scabrous in the inflorescence.

Leaves (3)4–6(7) cm long, about 1.5–2 mm broad at the base, shorter than the culm (in well developed individuals), erect, folded or revolute (slightly M-shaped in cross section) and ending in an acute tip, papillose, margins and dorsal midvein scabrous, reddish-brown at base but otherwise bright green.

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 1 terminal male spike and 2–3 lateral female spikes. Lowest bract with sheath ca. 1 mm and blade of variable length (4–12 mm), reaching below or above the inflorescence, upper bracts reduced to sheaths. Spikes erect to erectopatent. The apical male spike 3–5 mm × 1–1.5 mm, on a 1–2 mm erect peduncle, usually reaching a few millimetres higher than the uppermost female spike. Female spikes 3–6 × 2.5–3 mm, on 2–5 mm long peduncles. Scales acuminate to cuspidate, brown and with a broad white hyaline margin and green midvein. Perigynia subrotund, patchy brown and green, smooth, abruptly narrowing into a 0.3–0.5 mm distinct scabrous beak with oblique aperture. Stigmas 3.

Triangular nut within the perigynium.

Sexual reproduction by seeds; no vegetative reproduction. Seed set abundant in the few stands found. Seeds germinated to 8 % (Alsos et al. 2013). The sometimes large populations, especially in Nathorstdalen, vouch for efficient seed reproduction.

Fruits (inside perigynia) have no special adaptation to dispersal but are generally dispersed by wind, water and birds.

Carex glacialis may resemble both C. krausei and C. capillaris but differs from both of these in several features: In Carex glacialis the perigynia are subrotund with an abruptly narrowed, very slender beak and the sheaths of the bracts are very short (ca. 1 mm) and hyaline. In C. capillaris and C. krausei the perigynia are more spindle-shaped and gradually narrowed into an extended beak, and the sheaths of the bracts are several millimetres long and green. However, all the three species form very dense and small tussocks with narrow, green leaves.

Growing in stable parts of southfacing slopes and in well developed heath. Only found on calcareous substrates. Often with Dryas octopetala and/or Cassiope tetragona.

Thermophilous. Restricted to the middle arctic tundra zone and the weakly continental section. The species is known only from five small areas in Spitsbergen: the Uversøyra – Bogegga area south of Brøggerhalvøya (Oscar II Land), the Blomstrand area at Kongsfjorden (Haakon VII Land), Kapp Smith (James I Land) and Nathorstdalen (Dickson Land) at Dicksonfjorden and Wordiekammen (Dickson Land) at Billefjorden in the Isfjorden area.

The general distribution is circumpolar where it is frequent in the shrub and southern arctic tundra and scattered in the middle arctic tundra zone. In Europe it reaches south to S Norway.

The rarity of Carex glacialis in Svalbard is perhaps surprising. This is a hardy species reaching far north in Canada, Greenland and Russia but not the northernmost zones. The first finds were made as late as in 1988 (by A. Elvebakk), which means that the species has been overlooked for a long time and probably still is.

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.