This species is a formerly cryptic species in the Phaeocollybia kauffmanii complex; until it was described by Norvell (2000), from Van Damme State Park, in Mendocino County, California, USA. Before that P. benzokauffmanii was included in the concept of P. kauffmanii. Past collections have been examined and properly identified, and this species has been included in recent guides (Desjardin et al. 2015, Siegel et al. 2019), so most current records are being correctly identified.

Phaeocollybia benzokauffmanii is known from disjunct subpopulations from coastal Mendocino County, California, USA north into Washington State in the Coast Range and lower elevations of the Cascade Range in Oregon and Washington. Its population is widespread, but highly disjunct. This species appears to be restricted to mature and old growth forests, a habitat which is now rare and fragmented and continuing to decline in both quality and geographic extent due to logging and increased fire frequency and intensity. 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 this is 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.

This species is known from disjunct subpopulations from coastal Mendocino County, California, USA north into Washington in the Coast Range and lower elevations of the Cascade Range in Oregon and Washington.

Its population is widespread, but highly disjunct. This species appears to 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 due to logging and increased fire frequency and intensity. 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. Extrapolating these data to more northern sections of forests in 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 this is continuing into the future. It is suspected that the population will be declining at a similar rate.

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

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 has declined 90% in the last century (Society of American Foresters 1984, Haynes 1986). Fire is also a big threat to this species’ population. A stand replacing fire could severely degrade and/or diminish its current range.

No use/trade is known.

This species should be added to the United States Forest Service Northwest Forest Plan Survey and Manage list of rare/old growth forests dependent fungi. 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 populations are needed as is a better understanding of habitat restraints and requirements; e.g. is it restricted to old growth?