Entoloma nitriolens is a mainly arctic-alpine ectomycorrhizal fungal species associated with dwarf Salix in snowbed habitats, and Dryas in calcareous heaths. These habitats have been undergoing climate-driven decline in extent and quality through reduced snow cover, drying, and vegetation shifts during the last decades. Further habitat deterioration is predicted with continued biodiversity loss and decline of specialized alpine mycorrhizal fungal communities under ongoing and future climatic conditions. Based on these observed and projected habitat trends and the species’ ecological specialization, an ongoing and future global population reduction of at least 15% over a 50-year assessment period is conservatively inferred. The species is therefore assessed as Near Threatened (NT) under Criteria A3c+4c.

Entoloma nitriolens is close to E. politum, but as shown by Kokkonen (2024), E. nitriolens is phylogenetically clearly distinct from the latter, and is mainly an arctic-alpine species. It has formerly been called E. alpicola sensu Bjorbækmo (Brandrud et al. 2018).

Entoloma nitriolens is found mainly in arctic-alpine sites, in dwarf-Salix snowbeds, a nature type undergoing severe decline due to climate changes.

The species apparently has a fairly wide distribution in alpine (subalpine) Fennoscandia (Norway-Sweden-Finland, including arctic regions (Svalbard). The species is furthermore known from alpine Switzerland (from where it was described), and from Iceland and one, confirmed record from Alaska (Kokkonen 2024) as well as a couple of records from British Columbia, Canada (GBIF Aug 2026). (A few records from France, including the Pyrenees, could be (partly) correct, but need sequence-verification.)

The species is known from 8 sequence-verified localities from alpine Norway including arctic Svalbard (Brandrud 2018 with updates). It is furthermore known from 8 localities in Finland, including some lowland sites (Kokkonen 2024). The estimated, real/total number of localities in N Europe is 1 500. So far, the species seems to be rarer in alpine C Europe, and we estimated the total number of localities here to be 500 (high degree of uncertainty).  We further assume additional at least 1 000 localities according to the area of potentially suitable habitat in North America. This adds up to an estimated number of 3 000 localities worldwide. We assume on average 5- 10 fungal individuals (unique genotypes) per site each potentially comprising of several clones, resulting in a total population size of >30 000 mature individuals (cf. Dahlberg and Mueller, 2011).

Entoloma niotriolens is easily overlooked, has low detectability, and belongs to a taxonomically difficult species complex, while its alpine and arctic-alpine habitats are also relatively poorly surveyed for fungi. Known records therefore likely represent only a fraction of the true population. It is associated with alpine and arctic-alpine habitats In N Europe sometimes also in lowland Salix wetland habitats, where suitable habitat have been declining and are expected to continue to decline, particularly due to climate-driven vegetation change. Based on these habitat trends and the species’ ecological specialization, an ongoing global population decline of at least 15% over the next 50 years is conservatively inferred.

The species ectomycorrhizal fungal is mainly associated with rich and calcareous Salix herbacea-S. polaris snowbeds and calcareous Dryas-S. reticulata heaths. Its mycorrhizal association with Dryas octopetala has been documented from Svalbard (Brandrud et al. 2018). From subalpine Finland it is also documented from rich and moist forests-brooksides-rich fens (Kokkonen 2024).

Entoloma nitriolens has its major habitats in arctic-alpine dwarf Salix snowbeds as well as in calcareous Dryas heaths. The Salix snowbeds are undergoing continuing climate-driven change, including reduced snow cover, drying, longer growing seasons, and vegetation shifts that may reduce suitable dwarf-Salix habitat (Björk & Molau 2007; Sandvik & Odland 2014; Matteodo et al. 2016). The calcareous Dryas habitats are undergoing similar climate-driven changes and have little ability to migrate and lack suitable habitats at higher levels. Predictive studies indicate continued habitat and associated biodiversity loss and decline of specialized alpine mycorrhizal fungal communities under future climatic conditions (Niittynen et al. 2018; Arraiano-Castilho et al. 2024). The species restricted lowland wetland habitats are also declining due to areal loss and changed hydrology. Based on these observed and projected habitat trends and the species’ ecological specialization, an ongoing and future global population reduction of at least 15% over a 50-year assessment period is conservatively inferred. The species is therefore assessed as Near Threatened (NT) under Criteria A3c+4c, based on a suspected ongoing and projected population reduction inferred from continuing decline in the extent and quality of suitable habitat.

Conservation should focus on maintaining the extent, quality, and ecological integrity of known and potential arctic and alpine habitats and preventing avoidable local degradation from infrastructure development, intensive recreation, and other physical disturbance. Although the broader impacts of climate change cannot be addressed through species-specific conservation measures, protecting intact and well-connected arctic-alpine habitats may increase the resilience of Entoloma nitriolens and its host-plant communities to ongoing environmental change.

The concept and circumscription of Entoloma nitriolens has only recently been clarified (Kokkonen 2024). A reliable identification may still require DNA-based methods, records based on morphology alone may be uncertain. Targeted surveys in suitable habitats and molecular identification of specimens are therefore needed to clarify the species’ distribution, and improve baseline data on population status and trends. Without such data, declines may remain undetected and the severity of current threats difficult to assess.

There is no use and trade known, as it is considered to be poisonous.