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Caloboletus marshii D. Arora, C.F. Schwarz & J.L. Frank

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Scientific name
Caloboletus marshii
D. Arora, C.F. Schwarz & J.L. Frank
Common names
Ben's Bitter Bolete
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/195923616/195926787


Caloboletus marshii is a widespread bolete in the western United States. Most subpopulations are known from the range of its preferred ectomycorrhizal partner, Coast Live Oak. It is also occasionally found with other oak species around the Central Valley and Sierra Nevada foothills in California, and scattered populations are known from in the Willamette Valley of Oregon, and Columbia River valley in southern Washington. No decline has been reported and threats are expected to be localized. It is listed as Least Concern (LC).

Taxonomic notes

It was extensively detailed as Boletus "marshii" in Mushrooms Demystified (Arora 1986), but later formally described as Caloboletus marshii (Frank 2014).

Geographic range

This species occurs from southern California, USA, into Humboldt County in coastal/Coast range forests, typically with Coast Live Oak (Quercus agrifolia). There are scattered subpopulations inland around the Central Valley, and the Sierra Nevada foothills of California, and more rarely with Quercus garryana in the Willamette Valley of Oregon, and Columbia River valley into Washington.

Population and Trends

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

Population Trend: stable

Habitat and Ecology

It is ectomycorrhizal with oaks (Quercus spp.), especially Coast Live Oak (Quercus agrifolia). Typically fruiting occurs in late summer or early fall, even before the seasonal rains.


Urban development is leading to loss of habitat. Invasive plants, especially grasses growing in oak woodlands could also pose a threat.

Conservation Actions

Control of invasive plants in oak woodlands is needed, but no specific research is needed with regards to this species.

Use and Trade

There is no known use of or trade in this species.

Source and Citation

Siegel, N. 2021. Caloboletus marshii. The IUCN Red List of Threatened Species 2021: e.T195923616A195926787. https://dx.doi.org/10.2305/IUCN.UK.2021-2.RLTS.T195923616A195926787.en .Accessed on 28 September 2023

Country occurrence