Assessment Notes

Justification

Tricholomopsis fulvescens occurs in scattered disjunct subpopulations in the Cascade Range in Washington and Oregon, USA, with a single site in the Klamath Range in California. It has also been reported from Arizona but these collections need to be verified and are being excluded from this assessment. The species is only known from seven collections, so too few data of this species are available to characterize its habitat preferences with high confidence, but it appears to prefer old growth forests with large amounts of course woody debris. No Pacific Northwest collections have been reported in the past 25 years, despite being included on the Northwest forest plan Sensitive Species list, and actively surveyed for. Unsuccessful efforts were been made to relocate it at two of the historic Washington populations in 2014, 2017-2020. Given the low number of records, lack of sightings in 25 years including unsuccessful attempts at recollecting it from historical sites, and habitat loss over its reported range, this can be considered a rare species. Even multiplying the known number of records by up to 200-300 times based on suitable habitat only results in an population size estimate of 1,400-2,100 mature individuals occurring in several small, disjunct subpopulations of fewer than 250 mature individuals. High-intensity fires that consume large pieces of coarse woody debris result in a lack of appropriate substrate and habitat in large parts of its potential range, and as a result the species is considered to be in decline. Thus, it is precautionarily assessed as Endangered.

---

Taxonomic notes

This species was described from a collection made at Mount Rainier National Park, in Washington, USA (Smith 1960). Many western North American Tricholomopsis species remain poorly known, and diversity and species boundaries should be investigated.

---

Geographic range

Tricholomopsis fulvescens occurs in scattered disjunct subpopulations in the Cascade Range in Washington and Oregon, USA, with a single site in the Klamath Range in California. It has also been reported from Arizona; these collections should be verified, and are being excluded from this assessment.

---

Population and Trends

This species is only known from seven collections, so there are too few collections of this species have been made to characterize its habitat preferences with high confidence, but it appears to prefer old growth forests, which have lots of course woody debris. No Pacific Northwest collections have been reported in the past 25 years, despite being included on the Northwest forest plan Sensitive Species list, and actively surveyed for (Castellano et al. 1999). Unsuccessful efforts were been made to relocate it at two of the historic Washington subpopulations (field visits 2014, 2017-2020 by N. Siegel). Given the limited number of records, lack of sightings in 25 years including unsuccessful attempts at recollecting it from historical sites, and habitat loss over its reported range, this can be considered a rare species. Even multiplying the known number of records by up to 200-300 times based on suitable habitat only results in an population size estimate of 1,400 - 2,100 mature individuals occurring in several small disjunct subpopulations of fewer than 250 mature individuals.

Population Trend: Decreasing

---

Habitat and Ecology

This is a saprotrophic species found fruiting in the fall, growing solitarily or scattered on rotten conifer wood in mid- to high-elevation forests. It is a poorly known species with limited information on its habitat preference, other than most collections come from old growth forests.

---

Threats

Little is known about this species to make a robust assessment of possible threats, but high-intensity fires that consume large pieces of coarse woody debris result in a lack of appropriate substrate and habitat in large parts of its potential range (Steel et al. 2023).

---

Conservation Actions

Until more is known about this species' habitat restraints, no specific conservation actions can be identified with regard to this species beyond site protection and management to reduce fire frequency and intensity. Targeted surveys for this species are needed to better the understanding of its population trends and habitat restraints. Modern taxonomic work on Tricholomopsis in the Pacific Northwest is needed to resolve taxonomic issues and identify potential cryptic species.

---

Use and Trade

No use/trade is known.

---

Source and Citation

Mueller, G.M. 2025. Tricholomopsis fulvescens. The IUCN Red List of Threatened Species 2025: e.T273227667A273247530. Accessed on 25 November 2025.

---

• Country occurrence