Assessment Notes

Justification

Xerocomellus zelleri appears to be an uncommon but widely distributed bolete in western North America, however data to confirm this assumption are lacking due to confusion with X. atropurpureus; a recently described, and far more common 'cryptic species'. X. zelleri appears to have a preference for mature and old growth forests, but based on current information, we do not know if it is restricted to such habitat. It is locally common in old growth forests in Olympic National Park and other protected land on the Olympic Peninsula in Washington, USA, but it was not seen in the proximate surrounding forests which had been logged (N. Siegel field observations 2011, 2014, 2016). It appears to be rare across the rest of its range. Its population is likely too large to trigger listing under any threat category and as most of the known records are from protected areas, its population is inferred to be relatively stable. Without better information on its population size and trends to indicate that its population size is small, or declining at a rapid rate, it is assessed as Least Concern.

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Taxonomic notes

Work on western North American Xerocomellus (Siegel and Schwarz 2016, Frank et al. 2020) has shown that what was called X. zelleri was in fact the rarer of two different species, and the more common and widespread species, X. atropurpureus was then described.

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Geographic range

This species is found from southern British Columbia, Canada, south in coastal forests into northern California, USA, and in the Cascade Range in Washington, USA. Actual distribution information remains poorly known due to confusion of past records with the recently recognised, and much more common, Xerocomellus atropurpureus (Frank et al. 2020).

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Population and Trends

The population size and trend of this species are difficult to delimit as most published records under this name pertain to the recently recognised, cryptic Xerocomellus atropurpureus. It appears to be restricted to mature and old growth conifer forest. It is locally common in old growth forests in Olympic National Park and other protected land on the Olympic Peninsula in Washington, USA, but it was not seen in the proximate surrounding forests which had been logged (N. Siegel field observations 2011, 2014, 2016). It appears to be rare across the rest of its range. Frank et al. (2020) state "Despite extensive collecting over a six-year period in, we encountered this species only five times." Its population is probably too large to trigger listing under any threat category. As most of the known records are from protected areas, its population is inferred to be relatively stable.

Population Trend: Stable

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Habitat and Ecology

It is ectomycorrhizal with conifers, often fruiting on and around decaying moss covered stumps and logs, possibly restricted to mature and old growth forest.

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Threats

This is a ectomycorrhizal fungus species dependent on living host trees for viability. The major threat to this species and its co-occurring co-generic taxa is habitat destruction via the logging of old growth forests to which it appears confined to. The extent of old growth forest in the Pacific Northwest of North America declined 90% in the last century (Society of American Foresters 1984, Haynes 1986). The area is also experiencing an increase in fire frequency and intensity.

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Conservation Actions

Site protection and management to minimise threats are needed. New records of Xerocomellus zelleri need to be differentiated from X. atropurpureus. Detailed habitat notes are needed with new observations of this species to describe habitat limitations, its tree association and if it needs mature or old growth forests to produce sporocarps.

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Use and Trade

This species is edible, and occasionally collected for food.

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Source and Citation

Siegel, N. & Mueller, G.M. 2025. Xerocomellus zelleri. The IUCN Red List of Threatened Species 2025: e.T198481009A198487556. Accessed on 20 November 2025.

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• Country occurrence