• Proposed
  • 2Under Assessment
  • 3Preliminary Assessed
  • 4Assessed
  • 5Published

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
Proposed by
Noah Siegel
Comments etc.
Noah Siegel

Assessment Notes

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 & Frank (2014) described the three species, and erected the genus Butyriboletus for the group of closely related ‘butter boletes’.

Why suggested for a Global Red List Assessment?

Butyriboletus primiregius is a locally common species in true fir forests of the Sierra Nevada and Cascade Range, also recorded from Idaho.

Population is widespread, and no decline has been observed. We recommend it should be listed as Least Concern (LC).

Geographic range

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, and reported from the mountains in Idaho.

Population and Trends

Population is widespread and appears stable; no decline has been noted.

Population Trend: Stable

Habitat and Ecology

Ectomycorrhizal, associated with Abies sp. especially White Fir (Abies concolor) and Red Fir (Abies magnifica) in mid to high elevation forests of the Sierra Nevada and Cascade Range, and rare reports from the Rocky Mountains in Idaho. Fruiting 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, overall threat to the population is likely minimal.

Increase in fire frequency/intensityDroughts

Conservation Actions

Fuels reduction in mid to high elevation Abies forests.

Research needed

More data on populations and trends of this species.

Use and Trade

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


Arora, D. 1986. Mushrooms Demystified. Ten Speed Press: Berkeley, CA. 959 p.

Arora, D. & Frank, J.L. 2014. Clarifying the butter Boletes: a new genus, Butyriboletus, is established to accommodate Boletus sect. Appendiculati, and six new species are described. Mycologia 106(3): 464-480.

Thiers, H.D. 1975. California Mushrooms—A Field Guide to the Boletes. Hafner Press: New York, NY. 261 p


Country occurrence

Regional Population and Trends

Country Trend Redlisted