Mat-forming graminoid herb with an extensive system of horizontal, long, branched rhizomes with reddish brown, scaly leaves, typically with branch lengths of 4–10 cm between aerial shoots, forming very loose stands. Culms 8–15 cm.

Basal leaves 5–12 cm long, 1.5–2.5 mm broad, flat or more often folded, smooth or slightly scabrous in the apical part, with a M-profile with margins more or less revolute, mid vein depressed on the upper surface in a V-shaped groove that ends well below the apex, the apical part triangular in cross-section (this is a diagnostic character of Eriophorum species with flat leaves). Culms with 1–2 leaves above the basal leaves, similar to these, with a 1.5–2.5 cm long, not inflated sheath. Uppermost culm leaf attached at or about the middle of culm, with sheath little or not inflated, blade well developed, 2.5–5 cm long. Sheaths of culm leaves with a narrow hyaline margin without red cells.

Inflorescence a dense (early) to open (later) cluster of (1)2–6 globular spikes, before the wool stage 1.0–1.2 × 1.0–1.4 cm, in the wool stage up to 2.5 cm long, subtended by 1–6 bracts with (5)7(9) distinct veins, with dark grey mid parts and a narrow, white hyaline margin without red cells. The lowermost bract has an extended blade. Spikes sessile, subsessile or on 0.5–1 cm long peduncles with short, stiff hairs. Each flower subtended by a broadly triangular, acute to obtuse, greyish black scale with a paler grey margin and apical part (but not shiny silvery in the margin and without red cells). Flowers are bisexual, having 3 stamens with long anthers, 1.8–2.2 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 after the flowering stage. Wool white.

Each flower in the spike produces a nut.

Sexual reproduction by seeds; efficient local vegetative reproduction by rhizomes, forming stands that easily may become fragmented. Wind pollinated. Seed-set is probably intermittent and nuts do not seem to mature every year.

Nuts are efficiently spread by wind due to the attached wool. Dispersal of rhizome fragments by birds or water is possible.

The three taxa of Eriophorum in Svalbard are distingushed by several features. Eriophorum scheuchzeri has a single spike (head) with only scaly hyaline bracts, 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 ending 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. The anthers of E. triste are distinctly longer (1.–2.2 mm) than those of E. sorensenii (1.0–1.5 mm), and E. sorensenii has a very reduced uppermost culm leaf and some lower scales in the spikes with silvery hyaline margins, whereas E. triste has a well-developed blade on the uppermost culm leaf and no scales with silvery hyaline margins.

Eriophorum triste is a specialist of shallow mires and marshes on calcareous ground, almost always with abundant ground water (and sometimes submerged), on fine-grained substrates. The vegetation cover may be dense (moss carpets) but more often partly open.

Thermophilous. Nearly entirely within the middle arctic tundra zone and the weakly or clearly continental sections. Restricted to Spitsbergen and to the middle and inner parts of the Isfjorden, Kongsfjorden, Liefdefjorden and Wijdefjorden districts. The species is rather common in the calcareous areas north of Isfjorden, at Kongsfjorden, and at inner and middle Wijdefjorden, but rare elsewhere.

This is mainly an American arctic species, reaching across N Greenland to Svalbard and across the Bering Straits to NE Asia. The connection of the Svalbard population is obviously to the west.

There has been much controversy concerning whether E. triste is a worthwhile taxon or just a less significant part of the variation of the widespread E. angustifolium (see references in Elven et al. 2011). Novoselova (1994, 1998) argued for two species with little or no overlap in characters. This opinion is shared by almost everyone familiar with the two species in the field. The other viewpoint, that there is only one polymorphic species, is reflected by Ball & Wujek (2002) and others having limited field experience from the Arctic. Elven & Murray (in prep.) studied the variation in the E. angustifolium group in NW North America and found three well characterized taxa (E. angustifolium s. str., E. komarovii and E. triste), each with several diagnostic characters, with overlapping ranges but with very few intermediate plants and all of these with aborting anthers and fruits. This suggests that we are dealing with three distinct species. It also explains the rather strange description by Ball & Wujek (2002) in Flora of North America because these authors lumped the high arctic and alpine E. triste with the southern boreal E. komarovii inside one subspecies (due to both have hairy peduncles). In Europe, the problem is insignificant as E. triste never has been found on or close to the European mainland, whereas E. angustifolium never has been found in Svalbard.

Ball, P.W. & Wujek, D.E. 2002. Eriophorum Linnaeus. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico. 23. Magnoliophyta: Commelinidae (in part): Cyperaceae: 21–27.

Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF) Vascular plants. http://panarcticflora.org/

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

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

Novoselova, M.S. 1998. Nomenklaturnie kombinatsii v rode Eriophorum L. (Cyperaceae). – Novosti Sistematiki Vysshykh Rastenii 31: 7–9.