It forms low, reddish cushions in wet areas like bogs and poor fens across North America and Eurasia, particularly in regions with oceanic climates.

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.

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.

Sphagnum rubellum was originally described by the English bryologist William Wilson in 1855, who referred to it as "red dwarf bog-moss" due to its slender stems and small, reddish appearance.

Wilson noted that it is dioicous, meaning it has separate male and female plants, and he characterised its leaves as elliptical, obtuse, and subsucculent, with short, deflexed, attenuated branches.

Although S. rubellum bears some resemblance to S. acutifolium (now generally considered part of a broader species complex), Wilson distinguished it by its smaller size, neat appearance, and distinctive leaf shape.

Despite this, most modern taxonomists recognise S. rubellum as an independent species, distinguishable by its unique morphological and ecological traits under optimal growth conditions.

[7] Subsequent molecular analysis using microsatellite markers has further supported their status as distinct taxa, though there is evidence of high genetic variation within the red Acutifolia group as a whole.

Both S. andersonianum and S. bartlettianum show no significant genetic differentiation from S. rubellum, despite some morphological variations in features such as branch leaf arrangement and pore size.

[12] Sphagnum rubellum is found across the cool temperate regions of North America and Eurasia, in a belt-like pattern around the Northern Hemisphere (circumboreal distribution).

[14] In Britain, S. rubellum is particularly abundant in southern and western regions, where it largely displaces S. capillifolium, which is restricted primarily to upland areas such as the Pennines.

This habitat preference contrasts with S. capillifolium, which favours minerotrophic conditions and typically forms compact hummocks on relatively dry ground in shaded forests and open subarctic heaths.

[7] Sphagnum rubellum grows in bogs and poor fens (wetlands with some groundwater input), occurring in habitats ranging from raised mounds (hummocks) to flat areas (lawns).

[18] This reduced productivity under standard lab conditions suggests that current growth media may not be fully optimised for S. rubellum, potentially reflecting its specific habitat adaptations.

This relatively low but stable growth rate, combined with high decay resistance, represents an evolutionary strategy characteristic of section Acutifolia species.

Even under such rapid evaporation, the plant's efficient water transport system allows it to maintain stable growth in its characteristic low hummock habitat.

Laboratory experiments have demonstrated that S. rubellum can recover well from temporary periods of drought or flooding, though prolonged deep inundation may impair growth, especially when carbon dioxide concentrations in the water layer are low.

The presence of vascular plant clumps (tussocks) can create favourable microclimatic conditions that help S. rubellum survive drier periods.

The species responds positively to increased temperatures, showing enhanced growth and biomass production at 20 °C (68 °F) compared to 15 °C (59 °F), aligning with its relatively southern distribution.

When exposed to elevated ozone levels, S. rubellum experiences reduced growth and lower photosynthetic rates, though it maintains stable chlorophyll levels—indicating moderate resilience.

Comparatively, it displayed greater growth in open environments than in charcoal-filtered chambers, suggesting that field conditions may buffer some effects of ozone exposure.

[17] In peat bogs, Sphagnum rubellum provides a relatively dry microhabitat supporting diverse communities of oribatid mites, small soil arthropods involved in decomposition processes.

Local habitat characteristics, such as vascular plant diversity and groundwater level, strongly influence these mite communities, while geographic distance between bogs has minimal effect.

[29] Sphagnum rubellum underwent a significant range expansion during the Atlantic period (approximately 7500–5000 years before present), coinciding with the development of nutrient-poor (oligotrophic) plant communities across Central and Northern Europe.

This pattern of reduced genetic diversity in Central European populations is similar to that seen in other plant species that survived in restricted areas during glacial periods.

During glacial periods, the drier climate would have significantly restricted the available habitat for this moisture-dependent species, likely contributing to the formation of isolated populations in separate refugia.

[13] Modern genetic analysis indicates that the Neotropical populations of section Acutifolia (including S. rubellum) originated from a single northern (boreal) ancestor, though the exact relationships between groups remain unclear due to conflicting evidence from different genes.

Research has shown that when dead plant material from these species mixes with S. rubellum, it can accelerate decomposition, potentially undermining the peatland's ability to store carbon.

It is categorised as vulnerable in Luxembourg, near threatened in Switzerland, Serbia, and Slovenia, and is given various protective designations in parts of Russia, including classification as a rare species in both the Mari El Republic and Ulyanovsk Oblast.

This taxonomic ambiguity has made it challenging to accurately map the species' distribution in some regions, including the United Kingdom, where the two taxa have not been consistently distinguished in historical records.