Sphagnum rubellum, the red peat moss, is a species of peat moss in the family Sphagnaceae. It forms low, reddish cushions in wet areas like bogs and poor fens across North America and Eurasia, particularly in regions with oceanic climates. The species can vary in colour from green to pink or deep crimson, and grows up to 10 cm (3.9 in) tall. Like other peat mosses, it plays an important role in forming and maintaining peatlands.

This species is closely related to S. capillifolium, with which it was historically confused, though genetic studies have confirmed them as distinct species. While they can occasionally interbreed where their populations overlap, they typically occupy different habitats – S. rubellum preferring open, wet bogs while S. capillifolium grows in drier, more shaded areas.

Sphagnum rubellum is particularly well-adapted to wet, nutrient-poor conditions. It can transport water efficiently through its stems and maintain stable growth even when raised above the water table. While it grows more slowly than many related species, it is very resistant to decay. The species provides good conditions for tree seedlings to germinate, though its continued growth can later prevent young trees from establishing.

Though classified as a least-concern species in Europe and secure in North America, S. rubellum faces threats from peatland drainage, commercial harvesting, and air pollution, particularly nitrogen deposition. It is considered vulnerable or threatened in parts of its range, especially in central and southeastern Europe. Genetic studies suggest the species survived the last ice age in at least two separate refugia in Europe, which has influenced its current patterns of genetic diversity.

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