Assessment Notes

Justification

Butyriboletus persolidus is a locally common bolete, growing with oaks in western North America from sites in coastal and coast range forests in California, central and northern Sierra Nevada foothills, and with Quercus garryana in the Willamette Valley of Oregon and southern British Columbia, Canada. While it is not commonly recorded, and limited data are available to rigorously identify population trends, given its broad range and lack of specific threats, its population is likely relatively stable. It is assessed as Least Concen.

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Taxonomic notes

Long called by the European species, Boletus appendiculatus Schaeffer (Thiers 1975, Arora 1986), the western North American species was described as a distinct species, and the group of closely related "butter boletes" were given a new genus, Butyriboletus (Arora and Frank 2014).

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Geographic range

Butyriboletus persolidus is known from coastal and coast range forests in California from Monterey County to Mendocino County, and in the Sierra Nevada foothills from the central and northern part of the range. It is rare in the Pacific Northwest, where it has been reported with Quercus garryana in the Willamette Valley of Oregon and southern British Columbia, Canada.

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Population and Trends

The species has been reported over a broad area of far western US and Canada associating with oaks. While it is not commonly recorded and limited data are available to rigorously identify population trends, given its broad range and lack of specific threats, its population is likely to be relatively stable.

Population Trend: Stable

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Habitat and Ecology

The species is ectomycorrhizal with hardwoods, especially oaks (Quercus spp.). It forms sporocarps in the fall; especially in seasons with substantial early rainfall.

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Threats

This species occurs across a fairly widespread area with oaks (Quercus spp.) and possibly other hardwoods. No threats have been directly linked to this species. This species tends to fruit in seasons with early fall rains, and research into trends due to climate change, and the fall rainy season occurring much later in the year should be investigated.

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Conservation Actions

No specific conservation actions have been identified with regards to this species. Efforts to better document the species distribution and population trends is needed. Research into the effect of the later arrival of seasonal rain due to climate change is having on the species phenology is also needed.

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Use and Trade

This species is edible, and is often collected for food.

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Source and Citation

Siegel, N. 2022. Butyriboletus persolidus. The IUCN Red List of Threatened Species 2022: e.T217580629A217581897. Accessed on 22 November 2025.

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• Country occurrence