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

Butyriboletus querciregius D. Arora & J.L. Frank

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Scientific name
Butyriboletus querciregius
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 querciregius is a pink-capped butter bolete, growing with oaks in USA.

This species occurs over a widespread range, but is known from a limited number of records, and not enough data is available to assess trends, therefore I recommend listing it as Data Deficient (DD).

Geographic range

Growing with oaks (Quercus spp) in coastal and coast range forests in California from San Diego County northward, and in the Sierra Nevada and Cascade Range foothills into the Pacific Northwest, where it occurs with Oregon White Oak (Quercus garryana) in the Willamette Valley of Oregon, and Columbia River Valley in Washington; and possibly into southern British Columbia, Canada.

Population and Trends

Population occurs over a widespread area, but with a fairly limited number of records (iNaturalist 2021). Being a recently described species (Arora & Frank 2014), in the ‘Boletus regius’ complex, pre-2014 records need extra scrutiny.

Population Trend: Uncertain

Habitat and Ecology

Ectomycorrhizal with oaks (Quercus spp.), especially Coast Live Oak (Quercus agrifolia) in California, and Oregon White Oak (Quercus garryana) in the Pacific Northwest. Fruiting in fall, especially in seasons with substantial early rainfall.

Temperate Forest


This species occurs across a fairly widespread area with oaks (Quercus spp.). No threats have been directly linked to this species. Overall, the habitat has threats from urban development leading to loss of habitat and invasive plants, especially grasses growing in oak woodlands.
This species tends to fruit in seasons with early fall rains; research into trends due to climate change, and the fall rainy season occurring much later in the year should be investigated.

Housing & urban areasAgro-industry farmingUnspecified speciesDroughts

Conservation Actions

Control invasive plants in oak woodlands.

Site/area protectionSite/area management

Research needed

More data on populations and trends of this species; is climate change affecting this species.

Population size, distribution & trendsPopulation trends

Use and Trade

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

Food - human


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.

iNaturalist. 2021. http://www.inaturalist.org

Siegel, N. and Schwarz, C. 2016. Mushrooms of the Redwood Coast. Ten Speed Press: Berkeley, CA. 601 p.

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