Assessment Notes

Justification

Phaeocollybia pseudofestiva's population is widespread, but highly disjunct. It is currently known from ~35 localities and 50 plus records. This species may be restricted to mature and old growth forests. Suitable habitat is now rare and fragmented, and continuing to decline in both quality and geographic extent. The scarcity of remnant old growth and mature forests in the Coast Range and Cascade foothills, and their fragmented condition are a major cause for concern; it is unknown if this species is capable of colonising and persisting in younger forests. Steel et al. (2023) calculated that over 30% of the conifer forests in the southern Sierra Nevada Mountains transitioned to non-forest vegetation between 2011-2020 and that between 50-85% of mature forests significantly declined in quality during this time. Extrapolating these data to more northern California into Washington State yields a conservative estimate of a loss / decline of at least 30% of habitat for this species over the past three generations (50 years) and continuing into the future. It is suspected that the population will be declining at a similar rate. It is assessed as Vulnerable A2c+3c+4c.

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Taxonomic notes

Phaeocollybia pseudofestiva is often mistaken for the more common P. olivacea and P. fallax. All three can grow in close proximity; some collections identified as P. pseudofestiva contain fruitbodies of one or both of these species (Norvell and Exeter 2009).

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Geographic range

This species is known from disjunct subpopulations from coastal Mendocino County, California, USA north to Vancouver Island, British Columbia, Canada in Cast and Coast Range forests, and scattered location in the Cascade Range in Oregon.

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Population and Trends

Its population is widespread, but highly disjunct. It is currently known from ~35 localities and 50 plus records (Norvell and Exeter 2009, Siegel et al. 2019, MyCoPortal 2024). This species may be restricted to mature and old growth forests. Suitable habitat is now rare and fragmented, and continuing to decline in both quality and geographic extent. The scarcity of remnant old growth and mature forests in the Coast Range and Cascade foothills, and their fragmented condition are a major cause for concern; it is unknown if this species is capable of colonising and persisting in younger forests. Steel et al. (2023) calculated that over 30% of the conifer forests in the southern Sierra Nevada Mountains transitioned to non-forest vegetation between 2011-2020 and that between 50-85% of mature forests significantly declined in quality during this time. Extrapolating these data to more northern California into Washington State and southern British Colombia yields a conservative estimate of a loss / decline of at least 30% of habitat for this species over the past three generations (50 years) and continuing into the future. It is suspected that the population will be declining at a similar rate.

Population Trend: Unknown

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Habitat and Ecology

It is ectomycorrhizal with conifers and possibly Tanoak (Notholithocarpus densiflorus), and possibly restricted to late seral stage and old growth forests. Fruitbodies are solitary or scattered in small patches, appearing in fall and early winter.

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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 this species has a preference for and an increase in fire frequency and intensity. The extent of old growth forest in the Pacific Northwest of North America has declined 90% in the last century (Society of American Foresters 1984, Haynes 1986). Climate change and droughts, along with forest management practices has made western forests highly susceptible to stand replacing forest fires. Fire is big threat to this species’ population. A stand replacing fire could severely degrade and/or diminish its current range.

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Conservation Actions

This species is included on the United States Forest Service Northwest Forest Plan Survey and Manage list of rare/old growth forests dependent fungi (Castellano et al. 2003), and has been actively surveyed for since the late 1990’s. Logging and machine clearing of understory vegetation should be limited in mature and old growth forest in areas where this species might occur. Continued surveys for existing subpopulations are needed to better understand population trends and habitat restraints and requirements; e.g. is it restricted to old growth?

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Source and Citation

Mueller, G.M. 2025. Phaeocollybia pseudofestiva. The IUCN Red List of Threatened Species 2025: e.T273227372A273246652. Accessed on 22 November 2025.

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• Country occurrence