Assessment Notes

Justification

Clavariadelphus occidentalis is a common and widespread species in western North America, occurring in both hardwood and conifer forests; from southern California north into Alaska. It appears to extend south through Mexico into Honduras. Reports from eastern USA likely refer to a different species.

Recent unpublished phylogenetic data has suggested multiple cryptic species in the C. occidentalis group. These cryptic species will need to be considered if a rigorous taxonomic revision is undertaken, but for now, C. occidentalis is assessed as Least Concern.

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Taxonomic notes

Clavariadelphus occidentalis was described by Methven (1989), from a collection made in Yuba County, California, USA. Prior to this, the western North American species went by the misapplied name Clavariadelphus pistillaris.

Unpublished sequence data suggest multiple species going by the name C. occidentalis (see Clements 2018).

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Geographic range

This species is widespread in western North America, from southeast Alaska, south to southern California, east to the Rocky Mountains. It is also reported from Mexico and Honduras. Records from eastern United States likely refer to a different species.

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Population and Trends

The population is widespread and appears stable. However, the possibility of multi cryptic species will need to be considered if a rigorous taxonomic revision is undertaken.

Population Trend: Stable

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Habitat and Ecology

It is ectomycorrhizal with hardwoods and conifers, in coastal and montane forests across western North America south through Mexico into Honduras.

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Threats

While local treats could impact some scattered parts of its range, no specific threats have been identified with regards to this species.

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Conservation Actions

No specific conservation actions are needed with regards to this species. Clavariadelphus in western North America are in dire need of modern taxonomic work, as preliminary phylogenetic data has suggested multiple cryptic species in the C. occidentalis group.

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Use and Trade

No use/trade is known.

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Source and Citation

Mueller, G.M. 2025. Clavariadelphus occidentalis. The IUCN Red List of Threatened Species 2025: e.T272184211A272184621. Accessed on 22 November 2025.

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• Country occurrence