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

Butyriboletus autumniregius D. Arora & J.L. Frank

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Scientific name
Butyriboletus autumniregius
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 autumniregius is an uncommon butter bolete, growing with conifers in California and Oregon, 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

Currently known from Santa Cruz County, California, USA, north into central Oregon, in coastal and coast range forests, and in the Sierra Nevada and Cascade Range foothills from central California into central Oregon. Uncommon over much of its range, most records come from Mendocino County, north into Oregon; rare south of Sonoma County, California.

Population and Trends

Population occurs over a widespread area, but with a 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

Known from the mixed evergreen coastal/coast range forests of Northern California, Sierra Nevada foothills, Siskiyou mountains in northern California and Oregon and the Willamette Valley and Cascade Range foothills of Oregon. Ectomycorrhizal; host still speculative, but believed to be with conifers, likely Douglas-fir (Pseudotsuga menziesii); other unverified associates (Arora and Frank 2014) include conifers SItka spruce (Picea engelmannii), fir (Abies spp.) pine (Pinus spp.), and the hardwood trees Tanoak (Notholithocarpus densiflorus) and Madrone (Arbutus menziesii).

Fruiting in fall, especially in seasons with substantial early rainfall.


This species occurs across a fairly widespread area with conifers; likely with Douglas-fir (Pseudotsuga menziesii) and possibly other conifers and hardwoods. No threats have been directly linked to this species. 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.

Conservation Actions

No specific conservation actions have been identified with regards to this species.

Research needed

More data on populations and trends of this species.

Use and Trade

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


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

Wood, M.G. and Stevens, F.A. 2020. MykoWeb; California Fungi. http://www.mykoweb.com/CAF/species/Butyriboletus_autumniregius.html

Country occurrence

Regional Population and Trends

Country Trend Redlisted