This species was described from a collection made in Sierra County, California, USA (Petersen 1988). Field identification can be tricky, as some collections are difficult to distinguish from the Ramaria rasilispora/magnipes complex without microscopic examination, and thus many sites are probably overlooked in the field. Coastal collections should be compared genetically with montane collections, as they may represent a distinct species.

Ramaria thiersii is an uncommon but widespread species in California and the Pacific Northwest, currently known from ~20 localities, but it probably under reported due to the difficultly in distinguishing it from the common R. rasilispora/magnipes complex without microscopic examination. Conservatively, there are up to 100 times the number of sites where the species occurs. Assuming 4-8 mature individuals at each site, its population size is estimated to be between 8,000-1600, nearly all in one subpopulation. Data to fully assess population trends are lacking, but past and ongoing habitat loss and decreases in habitat quality are likely to be negatively impacting the species. It nearly fulfils the conditions for listing as threatened under criterion C2a(ii) and so is assessed as Near Threatened.

In the mountains, Ramaria thiersii is known from the Sierra Nevada in California, the Cascade Range in California and Oregon, and the northern Rocky Mountains in Idaho. It is also reported from coastal collections in Mendocino County, California, USA and British Columbia, Canada; these collections should be regarded with some scepticism and be compared genetically with montane collections. They are not considered in this assessment.

The population occurs over a widespread area, with fairly continuous records in the Sierra Nevada range in California, plus into the Cascade Range and the Rocky Mountains in Idaho. Currently it is known from ~20 sites (Siegel et al. 2019, MyCoPortal 2024), but it is probably under-reported from the California mountains. Conservatively, there are up to 100 times the number of sites where the species occurs. Assuming 4-8 mature individuals at each site, its population size is estimated to be between 8,000-16,000, predominantly in one subpopulation. Data to fully assess population trends are lacking, but past and ongoing habitat loss and decreases in habitat quality are likely to be negatively impacting the species.

It is ectomycorrhizal with conifers, likely with fir (Abies spp.). Most collections come from drier montane conifer forest in the Sierra Nevada and eastern slopes on the Cascade Range. Fruiting is in spring or early summer. Many records do not include detailed habitat information. A few of the recent collections appear to be from areas with old growth or late seral stage Abies forests, but data tying this species to a specific habitat type are lacking.

This is an 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. 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 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 is included on the United States Forest Service Northwest Forest Plan Survey and Manage list of rare/old growth forests dependent fungi, and has been actively surveyed for since the late 1990’s (Castellano et al. 1999). It is included on the Oregon Natural Heritage rare fungi list (Oregon Biodiversity Information Center 2019), as a S2 species. Logging or machine clearing of understory should be limited in mature (or old growth forest) in areas this species in known to occur.

A better understanding of habitat requirements of this species, and if it is restricted to mature and old growth forests is needed. Continued surveys for this species are also needed, especially in the central and southern Sierra Nevada in California. Genetic research and modern taxonomic work comparing coastal and montane collections should be undertaken to clarify its distribution, population trends and habitat requirements.