closed-sheathed cottongrass

Closed-sheathed cottongrass is a sedge in the genus Eriophorum (family Cyperaceae) characterized by leaf sheaths that are fused to form a closed tube around the stem, a morphological feature distinguishing it from open-sheathed relatives. Cottongrasses are quintessential plants of northern peatlands, bogs, and acidic fens across the boreal and arctic zones of the Northern Hemisphere, producing conspicuous cottony white seed heads — modified perianth bristles elongating as fruits mature — that transform peat bogs into spectacular white-tufted landscapes in late spring and early summer. These plants are ecological keystones of Sphagnum-dominated peat bogs, contributing organic matter through their dense root systems that resist decomposition in waterlogged, oxygen-depleted conditions, driving peat formation over millennia. Eriophorum species serve as important food plants for ptarmigan, geese, and various invertebrates in arctic and subarctic ecosystems. Climate change threatens cottongrass habitats through warmer temperatures accelerating peat decomposition, altered hydrological regimes, and permafrost thaw that fundamentally transforms the structure of northern peatlands.