Assessment Notes

Justification

Rhizopogon ellipsosporus is known from a single site in the Coast Range of California, and scattered sites in the Siskiyou Mountains and Cascade Range in Oregon, USA. Based on the few collections made, it appears to be restricted to mature and old growth forests, which are under threat from fires, logging and climate change. It is listed as Imperiled (G2) by NatureServe (explorer.natureserve.org) with an estimate of only up to 20 element occurrences (locations). This is an hypogeous species and thus has low detectability and its population size is likely much larger than the few records indicate. Conservatively it is estimated that there are up to 100 times more sites than are the currently known records, each with 4-6 mature individuals, resulting in a conservative estimate of 3,200-4,800 mature individuals (8 sites x 100 x 4-6 individuals) distributed in small, scattered subpopulations of fewer than 1,000 mature individuals. It is assessed as Vulnerable.

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Taxonomic notes

Many Rhizopogon lack distinctive morphological characters, and can only be reliably identified with genetic sequences.

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Geographic range

This species is known from a single site in the Coast Range of California, and scattered sites in the Siskiyou Mountains and Cascade Range in Oregon, USA.

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Population and Trends

Currently this species is known from eight sites in northern California and Oregon. Based on the limited number of collections made, it appears to be restricted to mature and old growth forests, which are under threat from fires and logging. It is listed as Imperiled (G2) by NatureServe (2022) with an estimate of only up to 20 element occurrences (sites). This is a hypogeous species and thus has low detectability and its population size is likely much larger than the small number of records indicates. Conservatively it is estimated that there are up to 100 times more sites than are currently known records, each with 4-6 mature individuals resulting in a conservative estimate of 3,200-4,800 mature individuals (8 sites x 100 x 4-6 individuals) distributed in small, scattered subpopulations of fewer than 1,000 mature individuals.

Population Trend: Decreasing

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Habitat and Ecology

It is hypogeous, fruiting solitarily or scattered in duff or soil in old growth forests. It is ectomycorrhizal, likely associated with Douglas-fir (Pseudotsuga menziesii). Fruiting is in fall, more rarely in spring. This species is dependent on mycophagy (primarily eaten by small mammals) for spore dispersal, and is probably restricted to old growth forests.

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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 it appears confined to 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). 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

Protection of mature and old growth forests in the Pacific Northwest is needed. Logging and machine clearing of understory vegetation should be limited in mature and old growth forest in areas where this species might occur. More data are needed on its population size and trends along with details on its habitat requirements and restraints.

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Use and Trade

No use/trade is known.

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Source and Citation

Mueller, G.M. 2025. Rhizopogon ellipsosporus. The IUCN Red List of Threatened Species 2025: e.T273227915A273247298. Accessed on 22 November 2025.

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