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Butyriboletus primiregius D. Arora & J.L. Frank

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Scientific name
Butyriboletus primiregius
D. Arora & J.L. Frank
Common names
IUCN Specialist Group
Mushroom, Bracket and Puffball
Assessment status
Assessment date
IUCN Red List Category
Siegel, N.
Mueller, G.M.

Assessment Notes

The content on this page is fetched from The IUCN Red List of Threatened Species: https://www.iucnredlist.org/species/195923185/195926310


Butyriboletus primiregius is a locally common species in true fir forests of the Sierra Nevada and Cascade Range, which has also been recorded from Idaho. The species is widespread and no decline has been observed despite localized threats having been identified. It is assessed as Least Concern (LC).

Taxonomic notes

For many years, this species was one of three western North American 'cryptic' species being called Boletus regius Krombholz (Thiers 1975, Arora 1986). Arora and Frank (2014) described three new western North American species, and erected the genus Butyriboletus for the group of closely related 'butter boletes'.

Geographic range

This species is common in the mid- to high-elevation forests of the Sierra Nevada and southern Cascade Range in California, USA, continuing north in the Cascade Range in Oregon. It has also been reported from the Rocky Mountains in Idaho.

Population and Trends

The population is widespread and appears stable. No decline has been noted.

Population Trend: stable

Habitat and Ecology

It is ectomycorrhizal, associated with Abies spp. especially White Fir (Abies concolor) and Red Fir (Abies magnifica) in mid- to high-elevation forests of the Sierra Nevada and Cascade Range, with rare reports from the Rocky Mountains in Idaho. Fruiting occurs in spring and early summer.


Prolonged droughts and decades of fire suppression have drastically altered the high sierra forest, leading to thicker, denser, Abies-dominated forest. As a result, hotter, stand-replacing fires (rather than patchwork and understory burns) are commonplace, altering appropriate habitat drastically, and making it ill-suited for this species. However, due to the widespread nature of this species, the overall threat to the population is likely minimal.

Conservation Actions

Land management is required to ensure a reduction in the build up of 'fuel' for burns mid-to high-elevation Abies forests. Additionally, more data are needed on populations and trends of this species.

Use and Trade

This species is edible, and is often collected for food. Occasionally it is commercially harvested (especially in the Mount Shasta area of California), and sold under the name King Butter Bolete (Arora and Frank 2014).

Source and Citation

Siegel, N. 2021. Butyriboletus primiregius. The IUCN Red List of Threatened Species 2021: e.T195923185A195926310. https://dx.doi.org/10.2305/IUCN.UK.2021-2.RLTS.T195923185A195926310.en .Accessed on 26 September 2023

Country occurrence