Solitary graminoid herb growing in dense, sometimes large tussocks (to 40 cm in diameter), with extravaginal branching (outside leaf sheaths). Almost all leaves basal. Culms several per tussock (often 15–20 or more), up to 15–20 cm long, very slender (0.4–0.8 mm broad), weakly trigonous with weak ribs, very strongly (greyish) papillose on and between ribs, smooth or slightly scabrous on ribs just beneath the inflorescence, procumbent or curved with the inflorescence resting on the ground in the fruiting stage, with 2–3 prophylls (basal leaves without or only with a reduced blade), and 3–4 leaves on the lower part of the culm, increasing in length upwards on culm.

Leaves folded or involute, 3–10 cm long, shorter than culms, very narrow, 0.4–0.6 mm, with mid vein sharply raised on the lower surface and impressed on the upper surface, margins serrate in the upper part, pale greyish or bluish green due to being very densely papillose.

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 a dense cluster, 0.8–1.2 × 0.3–0.6 cm, of (1)2–3 spikes, all or only the apical one bisexual with female flowers at top (acrogynous). All spikes with scale-like bracts 2.5–3.5 × 1.2–3 mm, very broadly ovate, obtuse or subacute, dark brown, with broad (ca. 0.3 mm), white hyaline margin, and with a darker or paler mid vein which in the lowermost bract may continue as a subulate, serrate tip up to 5 mm. Scales of male and female flowers similar, 1.5–2.5 × 1.2–2.0 mm, broadly ovate, obtuse to subacute, brown with a slightly paler mid vein and a broad (0.2–0.3 mm), white hyaline margin. Perigynia elliptic in outline, lens-shaped (lenticular, with one nearly flat and one slightly rounded surface), 1.8–2.2 mm, tapering at base into a short foot and at top into an insignificant (less than 0.1 mm) beak truncate at the aperture, with more or less distinct veins, strongly papillose, olive brown. Stigmas 2.

Lenticular nut within the perigynium.

Sexual reproduction by seeds; no vegetative reproduction. Fruits mature regularly, often in large amounts, and are deposited on the ground due to the curved or prostrate culms.

Short distance dispersal is probably mainly by sea currents and freshwater streams but dispersal over longer distances by birds is highly probable. The site types of C. glareosa are frequently visited by migrating birds.

The two Svalbard species most closely related to C. glareosa, in the section Glareosae, are C. lachenalii and C. marina. Carex glareosa differs from both of these in the very narrow leaves (less than 0.6 mm broad) and slender culms (less than 0.8 mm broad), the culms are slender, curving or prostrate, and the abundant, greyish papillae on both leaves and stems giving them a bluish green appearance. In both C. lachenalii and C. marina the leaves and culms are more than 0.8 mm broad, stiff, erect or ascending, and green or yellowish green. The very short beak of the perigynium also distinguishes C. glareosa from both C. lachenalii (beak distinct, 0.2–0.4 mm) and C. marina (no beak whatsoever).

On seashores, mostly on sandy or gravelly plains, rarely on more fine-grained soils, occasionally also occurring some distance from the sea and above the tidal and wave zone (especially in Adventdalen near Longyearbyen). On well-drained, periodically dry soils. The majority of stands are inundated by sea water now and then but not regularly (i.e., upper geolittoral). Due to inundations and frequent sedimentation, the substrates are never acidic, but often salty.

Thermophilous. The entire range is within the middle arctic tundra zone and the weakly continental section. Restricted to Spitsbergen where it is found at the northern shore of Van Mijenfjorden (Nordenskiöld Land) as very rare, and at Isfjorden where it is rather frequent near Longyearbyen and in Adventdalen, otherwise very scattered in the Lands of Nordenskiöld, Sabine, James I, and Oscar II. The global range is circumpolar in the arctic and northern boreal zones, in Europe south to Iceland and S Scandinavia (from where it now is rapidly disappearing, probably due to climatic change or change of land use close to the sea).

Two varieties have been proposed: var. glareosa and var. amphigena Fernald. The varieties have rather different perigynia (see Halliday & Chater 1969a; Toivonen 2002) but do not differ in other characters and may be intergrading. The former is circumpolar; the latter is amphi-Atlantic in NW Europe, reported from Iceland, Fennoscandia, and NW Russia, and from Greenland and NE Canada. They may merit rank as races but should be confirmed to differ in more than a single character before acceptance. They were not accepted as separate races by Egorova (1999). The Svalbard material has not yet been studied as to varietal affinity or variation.

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.

Halliday, G. & Chater, A.O. 1969. Studies in the Carex glareosa complex. 1. Fruit-shape. – Feddes Repertorium 80: 77–92.

Toivonen, H. 2002. Carex Linnaeus sect. Glareosae G. Don. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico. 23. Magnoliophyta: Commelinidae (in part): Cyperaceae: 311–321