Butyriboletus autumniregius is an uncommon bolete growing with conifers in California and Oregon, USA. It occurs over a widespread range, but is known from a limited number of records, and not enough data is available to assess trends.  However, given its broad habitat and geographic range, the species population is likely relatively stable and no specific threats have been identified. The species is assessed as LC

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 three new western North American species, and erected the genus Butyriboletus for the group of closely related ‘butter boletes’.

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.  However, given its broad habitat and geographic range, the species population is likely relatively stable and no specific threats have been identified. The species is assessed as LC

The species is restricted to far western USA.  It is known from Santa Cruz County, California, 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. It is uncommon over much of its range with most records coming from Mendocino County north into Oregon; rare south of Sonoma County, California.

The species occurs over a widespread area associated with a range of potential mycorrhizal hosts, but with a limited number of records (iNaturalist 2021). As it is a recently described species (Arora & Frank 2014) in the ‘Boletus regius’ complex, pre-2014 records need extra scrutiny and the number of historical records will likely increase.  Given its broad habitat and geographic range, the species population is likely relatively stable.

The species is reported 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. It is ectomycorrhizal but its host associations are 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).  The species forms sporocarps (mushrooms) in the 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.

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

More data on populations and trends of this species are needed as well as research to identify mycorrhizal host preference.

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