Assessment Notes

Justification

Cortinarius sierraensis has been reported with Lodgepole Pine (Pinus contorta) in the Sierra Nevada mountains, often near lakes, streams or other water sources. Infestation by bark beetles and changes in fire frequency and intensity are threatening its habitat leading to a population declines in this species. Because of its bright reddish brown to orange brown colours, this is an easily seen species, thus the small number of reports suggests that this may be a very rare species. Additionally, this is a target species of the Fungal Diversity Survey West Coast Rare Fungus Challenge that is engaging citizen scientists to search for rarely recorded fungi in the region. This focused effort has only recovered two records (iNaturalist 2024). Thus, taking a precautionary approach it is estimated that that its population size is c.1,000-1,500 mature individuals occurring in small scattered subpopulations of fewer than 250 mature individuals. Thus it is assessed as Endangered.

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Geographic range

This species is known from five sites in the southern, central, and northern Sierra Nevada in California, USA (MyCoPortal 2024, iNaturalist 2024).

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Population and Trends

Currently this species is known from five collections / observations, two of which are historic. Subpopulations are from high elevation Lodgepole Pine (Pinus contorta) forests near water sources. Until 2023 it was only known from southern and central Sierra Nevada Mountains. An observation in 2023 from Lassen Volcanic National Park extended its known distribution in the northern part of the mountain range. Because of its bright reddish brown to orange brown colours, this is an easily seen species, thus the limited number of reports supports that it is a very rare species. Additionally, this is a target species of the Fungal Diversity Survey West Coast Rare Fungus Challenge that is engaging citizen scientists to search for rarely recorded fungi in the region. This focused effort has only recovered two records (inaturalist.org). Thus, taking a precautionary approach it is estimated that that its population size is approximately 1,000-1,500 mature individuals. This is based on; five known functional individuals multiplied by an estimated factor of 200-300 to take into account the conversion to mature individuals, per Dahlberg and Mueller (2011) and additional potential sites based on potential habitat, that have not been recorded so far. It is thought to occurs in small scattered subpopulations, consisting of fewer than 250 mature individuals.

Population Trend: Decreasing

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Habitat and Ecology

This is an ectomycorrhizal species. Fruitbodies are scattered, growing from duff and soil under Lodgepole Pine (Pinus contorta). It is only known from a few locations in higher elevation Lodgepole Pine forests in the Sierra Nevada mountains, often near lakes, streams or other water sources. Fruiting occurs in summer and early fall.

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Threats

Mountain Pine Beetle (Dendroctonus ponderosae) outbreaks, leading to large scale dieback in Lodgepole Pine forest and an increase in fire frequency and intensity are likely detrimental to this species. Cortinarius sierraensis may also be indiscriminately collected if found by dyers. Based on the limited information on the species’ distribution and details of its habitat preference additional threats may be important.

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Conservation Actions

Known subpopulations should be protected from logging, development and other disturbances. Targeted surveys of suitable habitat are needed to assess the presence or absence of this species.

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Use and Trade

Closely related species of Cortinarius are highly prized dye fungi. C. sierraensis would likely be collected if found by dyers.

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Source and Citation

Mueller, G.M. & Siegel, N. 2025. Cortinarius sierraensis. The IUCN Red List of Threatened Species 2025: e.T273194444A273246569. Accessed on 22 November 2025.

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