Assessment Notes

Justification

Suillus brunnescens is a widespread Suillus in western North America, occurring with five-needle pines across the western mountains. Five-needle pines are suffering declines from the introduced fungal pathogen White Pine Blister Rust (Cronartium ribicola), and subsequent attacks by the mountain pine beetle (Dendroctonus ponderosae). The impacts on this species are unclear, but, at present, are not thought to be causing declines to such an extent that the species would approach the thresholds for listing as threatened. Therefore, this species is assessed as Least Concern.

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Taxonomic notes

Suillus brunnescens was described based on a type collection made near Grants Pass, Oregon, USA (Smith and Thiers 1964). Suillus borealis (Smith et al. 1965), described from Idaho, is a synonym (Nguyen et al. 2017).

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Geographic range

This species is widespread in the mountains of western USA from the southern Sierra Nevada in California, north through the Siskiyou mountains and Cascade Range throughout the Pacific Northwest, east across the northern Rocky Mountains into southern Canada.

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Population and Trends

Suillus brunnescens is locally common and widespread in western North America, occurring with five-needle pines across the western mountains. Many five-needle pine species are however declining due to the introduced fungal pathogen White Pine Blister Rust (Cronartium ribicola).

Population Trend: Decreasing

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Habitat and Ecology

It is ectomycorrhizal with five-needle pines; especially Sugar Pine (Pinus lambertiana) in California, and Western White Pine (P. monticola) in the Pacific Northwest. Fruiting is in summer and fall, with young to mature trees.

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Threats

Many five-needle pine species are declining due to the introduced fungal pathogen White Pine Blister Rust (Cronartium ribicola), and subsequent attacks by the Mountain Pine Beetle (Dendroctonus ponderosae). Prolonged droughts and decades of fire suppression have drastically altered western montane forests, leading to thicker, denser, Abies-dominated forests. As a result hotter, stand-replacing fires (rather than patchwork and understorey burns) are commonplace, altering appropriate habitat drastically and making it ill-suited for this species.

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Conservation Actions

Continued work on breeding blister rust resistant pines is needed, and control of blister rust spread. The extent of this species' range and tree associations also require further study.

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Use and Trade

Suillus species are edible, but are not highly regarded and thus only occasionally collected.

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Source and Citation

Siegel, N. 2022. Suillus brunnescens. The IUCN Red List of Threatened Species 2022: e.T198478949A198487395. Accessed on 20 November 2025.

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• Country occurrence