Eriophorum vaginatum is one of the most abundant and distinctive plants in Alaska, found in low-lying, moist areas dominated by acidic soils and permafrost. Though called 'cottongrass' for the white, fluffy flowers, it is actually a member of the sedge family. Eriophorum vaginatum forms large, dense tussocks, which can dominate huge swaths of land, and make walking difficult and treacherous. The stems grow 10-60 cm tall, though the growth of the tussock can elevate the whole plant higher than that above the ground. Tussocks consist of many persistent dead leaves— though Eriophorum vaginatum may appear to dominate a landscape, living leaves and stems are often less abundant than they seem because of the volume of persistent dead material from these plants. Basal sheaths are 1-3 per stem. Leaves are filiform and triangular in cross-section. Spikes are solitary and upright, round to ovoid-oblong in shape, lacking involucralbracts. The scales subtending the highly reduced flowers are dark grey at the center with pale or transparent margins (distinguishing it from closely related tussock-forming E. brachyantherum and E. callitrix). Flowers are highly reduced and bisexual. The fruits are single-seeded, ovoid achenes with pointed tips, 2-3.5 mm long, surrounded by white bristles.
Eriophorum vaginatum is perennial and flowers in early summer.
Members of the genus Eriophorum are monoecious, with bisexual flowers. The flowers are wind-pollinated and the fruits wind-dispersed. Seeds of Eriophorum vaginatum germinate the best in disturbed soils. Seeds can germinate almost immediately after dispersal (not requiring stratification) and can remain present in the seedbank for several years, but their viability declines with time (Innes 2014). tussocks can survive fires, and rapidly regenerate and produce many new seedlings. This species does not spread vegetatively via rhizomes.
The 'cotton' of the flowering head was traditionally used by Alaska Natives as stuffing, or as a firestarter.
Eriophorum vaginatum has a widespread circumpolar range. In North America, E. vaginatum ranges from the northeastern United States, through eastern and northern Canada to Alaska. In Alaska, E. vaginatum is found throughout much of the state, except for the Aleutians and Southeast Alaska. In Denali, E. vaginatum is common, widespread and locally abundant north of the Alaska Range.
Eriophorum vaginatum is most abundant at low to moderate elevations where it has a 50% probability of occurring at any site under 300 meters, but its cover is highest at 300-500 meters. It is more abundant and has much higher covering on north-facing (or east/west facing) slopes, but in general has a strong preference for more level terrain. The average slope for all recorded occurrences is only 3 degrees. If a site in Denali is less than 4 degrees incline, there is a more than 35% chance Eriophorum vaginatum will be found there.