Assessment Notes

Justification

Lactarius rubriviridis is currently known from three locations, two in California and one in Oregon. Despite yearly attempts to relocate it at the type location, it has not been found there since. Given that this is a hypogeous fungus, its detectability is low and it is likely under-collected. It faces plausible threats to its habitat from forest management, stand-replacing fires and bark beetle outbreaks. Given that it is known from only three locations and has not been recorded in 20 years, such threats could drive the species to extinction in a short time, so precautionarily it is assessed as Vulnerable D2.

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Taxonomic notes

This species was described by Desjardin (2003) based on two collections, made nineteen years apart. The type collection came from Tahoe National Forest, in Sierra County, California, USA.

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Geographic range

This species is known from two collections (from 1,350 and 1,800 m in elevation) in the central and northern Sierra Nevada mountains in California, and a single site in “central Oregon” (Kuo 2009), presumed to have been made in the eastern Cascades.

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Population and Trends

Little is known about the habitat associations of this species. It appears to be quite rare; with only three collections. Despite yearly attempts to relocate Lactarius rubriviridis at the type locality, it has not been seen there since 2001. Given that it is known from only three locations, its threats could drive the species to extinction in a short time.

Population Trend: Unknown

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Habitat and Ecology

It is hypogeous, solitary or scattered, buried under duff, and is ectomycorrhizal with Pinaceae; known sites have both pine (Pinus spp.) and fir (Abies spp.). Both California collections have been found in disturbed areas (campgrounds), fruiting in spring. More work is needed to describe the species’ habitat associations and limitations. This species is likely dependent on mycophagy (primarily eaten by small mammals) for spore dispersal. However, unlike many sequestrate fungi, this species has retained the ability to forcibly discharge spores, and is, at least partially, wind dispersed.

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Threats

Too little is known about habitat preferences to assess in particular, but in general the changes in forest management and especially fire suppression have changed the composition and structure of Sierra Nevada forests, resulting in fir-dominance, and a higher risk of stand replacing wildfires. Furthermore, an increase in very dry winters has caused bark beetle outbreaks resulting in high mortality of conifers, especially pines.

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Conservation Actions

Sites should be protected from logging or other major disturbance. More work is needed to describe the species’ habitat associations and limitations, and pinpoint potential threats. Targeted surveys for additional subpopulations should be carried out.

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Use and Trade

There is no use/trade.

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Source and Citation

Siegel, N. & Mueller, G.M. 2025. Lactarius rubriviridis. The IUCN Red List of Threatened Species 2025: e.T273195792A273245058. Accessed on 23 November 2025.

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• Country occurrence