An important ecosystem engineer in peatlands, S. angustifolium influences carbon cycling through its decay-resistant tissues and shows considerable resilience to climate change, maintaining stable growth patterns even under warmer and drier conditions.

The species is dioicous, producing spore capsules in late summer, and invests significantly in chemical defences to protect its reproductive structures.

It plays a key role in the ecological succession of peatlands, particularly in areas recovering from permafrost thaw, where it forms intermediate "lawn communities" that mark the transition from wet post-thaw conditions to drier hummock vegetation.

Its genome of 395 megabases shows unique adaptations for bog environments, including specialised pathways to manage pH stress through hormone expression and cell transport mechanisms.

[12] The plant typically appears green or yellowish in colour, and to the untrained eye may resemble its close relatives S. recurvum, S. fimbriatum, or S. capillifolium.

Along the stem are small triangular leaves, 0.7–1.0 mm long, that hang downward, featuring blunt tips that often appear worn and a distinctive broad border at their base.

[4] The most reliable microscopic feature for identifying S. angustifolium (except when comparing it with S. balticum) is the structure of its hanging branch leaves, which have distinctive large pores on their outer surface near the leaf tips.

The moss's vigorous lateral spread capability is particularly evident under favourable conditions, where it can significantly expand its coverage area through vegetative growth.

[13] Sphagnum angustifolium shows considerable morphological variation, particularly in southern parts of its range where identification becomes more challenging due to less distinct characteristics.

[4] The most significant taxonomic confusion occurs within the S. recurvum complex, particularly between S. angustifolium and S. flexuosum, which show some genetic overlap despite being distinct species.

[3] In exposed, wet areas, particularly in the upland regions of northern and western Britain, S. angustifolium might be confused with ground-growing forms of S. cuspidatum.

[4] Globally, S. angustifolium has a circumboreal distribution (occurring throughout the northern regions of Europe, Asia, and North America) with a distinct preference for continental rather than coastal areas.

[4] Studies have documented its presence across numerous European countries, including Bulgaria, Croatia, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Latvia, Lithuania, Montenegro, Norway, Poland, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, and the United Kingdom.

[4] In the British Isles, S. angustifolium is most frequently encountered in locations where there is a distinct flow of mineral-enriched water, favouring the more nutrient-rich end of its ecological tolerance range.

[15] Unlike some Sphagnum species that are restricted to specific microhabitat conditions, S. angustifolium shows considerable flexibility in its habitat requirements within collapse scar environments.

This adaptability allows it to persist across a range of moisture conditions, though it tends to be most abundant in areas with moderate water tables that have had time to stabilise after initial permafrost thaw.

[16] The male structures are often conspicuous, surrounded by brightly coloured yellow or pale orange modified leaves that contrast sharply with the plant's normal green foliage.

[4] The male structures are often conspicuous, surrounded by brightly coloured yellow or pale orange modified leaves that contrast sharply with the plant's normal green foliage.

[4] Female plants develop swollen archegonia (reproductive organs), which then mature into light yellow-brown spore capsules supported by a stalk (seta).

[4] The species produces relatively small spores (approximately 25 μm in diameter) with sparse surface protrusions on their outer layer (perispore).

It either forms pure carpets or grows alongside other peat moss species, such as Sphagnum riparium, S. flexuosum, S. fusbum, S. subnitens, S. recurvum var.

[11] Sphagnum angustifolium supports various invertebrates (animals without backbones) in peatland ecosystems, including ants, ground beetles (Carabidae), and non-biting midges (Chironomidae).

[16] When growing in favourable conditions with consistent moisture and adequate nutrients, S. angustifolium shows remarkable resilience to damage from herbivores.

Even under environmental stress, such as warming or reduced precipitation, S. angustifolium maintains its biomass production and decay-resistant properties, ensuring the continuity of its ecosystem functions.

S. angustifolium communities show rapid ecological turnover; for example, studies in northwestern Canada report a 30% change in composition over a decade, highlighting its transitional role in succession.

Its success depends on transplant size, with larger plugs (10–15 cm in diameter) showing better survival and growth, likely due to improved moisture retention.

However, its establishment is strongly affected by local moisture conditions, underscoring the importance of maintaining suitable hydrological environments for recovery.

[13] Sphagnum angustifolium demonstrates resilience to climate change, maintaining stable morphology and growth under experimental warming and reduced precipitation.

Even with a 37% reduction in nighttime precipitation, it maintains growth patterns and chlorophyll concentrations, reflecting efficient water retention and sustained photosynthesis.

In nutrient-poor peatlands, it maintains stable production after water level changes, sometimes increasing biomass during warmer growing seasons.