Mat-forming graminoid herb with very long, branched horizontal rhizomes with scaly leaves, forming diffuse stands potentially being tens or hundreds of meters in diameter. Erect aerial shoots up to 25 cm or more.

Basal leaves 10–25 cm, narrow, involute, smooth. Flowering shoots with 1–2 basal leaves similar to those of vegetative shoots and 1–2 short culm leaves, the upper one attached at or below the middle of the culm, with slightly inflated sheaths and reduced blades. Sheath of the upper culm leaf with a narrow hyaline margin with very few if any red cells (see Comments).

Inflorescence a single globular terminal spike, 0.8–1.2 × 0.8–1.1 cm in flowering stage, up to 3.0–4.5 × 3.5–5.5 cm in fruiting stage, subtended by a few bracts with dark grey middle part and a broad shiny (silvery) hyaline margin constituting 1/3 or more of the width of the upper part of the bract, with very few if any red cells. Each flower subtended by a scale similar to the bracts but with even broader hyaline margins, apex broadly triangular. Flowers are bisexual with 3 stamens with short anthers, 0.8–1 mm, and a one-seeded gynoecium with 3 stigmas. Stamens and gynoecium are surrounded by a ring of hairs (transformed tepals) attached to the base of the gynoecium and elongating strongly as wool in the fruiting stage. Wool shiny white.

Each flower in the spike produces a nut.

Sexual reproduction by seeds; efficient local vegetative reproduction by rhizomes, resulting in very extensive stands that easily may become fragmented. Wind pollination. Flowering and seed-set is regular, and nuts seem to develop in most years. Germinability of seeds is low (7–10 %) but this may be due to difficulties in germinating this species in the laboratory (Alsos et al. 2013; Müller et al. 2011).

Fruits are efficiently spread by wind due to the attached wool. Dispersal of detached rhizome fragments between sites, by birds or water, is probable.

The three taxa of Eriophorum in Svalbard differ from each other in several features. Eriophorum scheuchzeri has a single spike (head) where all the bracts are scaly and hyaline, whereas both E. sorensenii and E. triste have two or more spikes with one or more extended, firm, leaf-like bracts. Eriophorum scheuchzeri and E. sorensenii both have filiform involute leaves, whereas E. triste has flat leaves with a V-shaped depression on the upper surface that ends well below the apex. In E. triste, the 2–4 spikes are all of the same size and sit on short, but distinct, peduncles, whereas E. sorensenii usually has one large spike and 1–2 smaller, subsidiary ones, all subsessile.

Nearly confined to mires and wetlands with wet or even periodically inundated conditions. Sometimes occurring as a pioneer on newly established, wet river bars, sediment plains and in deltas. On fine textured soils such as clay, silt or fine sand with poor drainage or stagnant water. Seems to be indifferent as to soil reaction (pH). Probably much grazed by reindeer and also by geese (feeding on the rhizomes).

Hardly thermophilous but absent from the harshest parts of Svalbard. Common in the middle and northern arctic tundra zones, barely penetrating the polar desert zone. Common in all sections. Common on Spitsbergen and recorded from some sites on Edgeøya and Nordaustlandet. Not recorded from Bjørnøya.

Eriophorum scheuchzeri ssp. arcticum is circumpolar in the northern arctic zones. It is replaced by ssp. scheuchzeri in the southern arctic and the boreal zones and this race also reaches more southern mountains, especially in Europe where it is found south to the Pyrenees, the Alps and the Balkan mountains.

The mainland race of Eriophorum scheuchzeri – ssp. scheuchzeri – differs from the Svalbard race – ssp. arcticum – in several characters, foremost in bracts much narrower with a very narrow and not silvery hyaline margin, with very numerous red cells, often as stripes, in the bracts and also in the sheaths of culm leaves, with a canaliculated and often yellowish apex on bracts, but also in culm width (1.2–1.5 mm in ssp. scheuchzeri, 1.0–1.2 mm in ssp. arcticum), and in the shape of the fruiting spike. When the wool is fully developed, the head of ssp. scheuchzeri has a globular shape, whereas that of ssp. arcticum is bell-shaped. For additional differences, see Novoselova (1994), Cayouette (2004), and Elven & Murray (in prep.). No transitions are observed in W Europe and few if any in Greenland, North America or Russia. The only reason for not accepting the two taxa as independent species is presence of some pollen-fertile intermediates in Alaska (Elven & Murray in prep.).

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.

Cayouette, J. 2004. A taxonomic review of the Eriophorum russeolum–scheuchzeri complex (Cyperaceae) in North America. – Sida 21: 791–814.

Elven, R. & Murray, D.F. In prep. The cottongrasses (Eriophorum L., Cyperaceae) of Alaska and Yukon Territory revisited.

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.

Novoselova, M.S. 1994. Sistema roda Eriophorum (Cyperaceae). I. Podrody Erioscirpus, Eriophoropsis, Phyllanthela. – Botanicheskii Zhurnal 79(11): 77–89.