Assessment Notes

Justification

Lactarius crassus is a sequestrate species which occurs in higher-elevation fir forest in the Sierra Nevada, southern Cascade and Klamath Ranges, with around 25 known localities. It may benefit from management practices that have resulted in the expansion of fir forest, and it is listed as Least Concern.

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Taxonomic notes

This species was originally described as Arcangeliella crassa from a collection made in Stanislaus National Forest, California, USA (Singer and Smith 1960). Thiers (1979) considered Arcangeliella tenax a distinct species, but subsequent work by the same author (Thiers 1984) synonymized A. tenax within A. crassa based on the considerable degree of overlap in their characters.

These sequestrate Lactarius have been called Arcangeliella. However, it is a fruitbody form that has evolved multiple times within the genus Lactarius, and most species have been formally transferred to Lactarius.

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Geographic range

This species is widespread in mid- to high-elevation forests in the Sierra Nevada, southern Cascade and Klamath Ranges in California, and more rarely in the Oregon Cascades.

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Population and Trends

This species was thought to grow mainly in mature and old-growth fir forests, however field work during the 2016 and 2017 season (N. Siegel pers. obs. for USFS) found a number of collections in young Abies forests. It was found three times during the "2011–2013 Survey & Manage" surveys in northern California, and has a few other recent records on Mushroom Observer (2020). It is uncommon in the California mountains, but there are not enough data available to infer population trends. It is possible that, with the expansion of fir (Abies)-dominated forests in the Sierra Nevada, the population are increasing.

Population Trend: unknown

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Habitat and Ecology

It is solitary, scattered or in small clusters; fruitbodies are partially buried, or more rarely completely buried in duff. It is ectomycorrhizal, associated with firs (Abies spp.), in mid- to high-elevation forest of the Sierra Nevada, Cascade Range and Klamath Mountains, and is found in young to mature forests. Fruiting occurs in late spring into fall, most commonly in early summer. This species is likely dependent on mycophagy (primarily eaten by small mammals) for spore dispersal.

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Threats

Prolonged droughts and decades of fire suppression have drastically altered western montane forests, leading to thicker, denser, Abies-dominated forests. As a result hotter, stand-replacing fires (rather than patchwork and understorey burns) are commonplace, altering appropriate habitat drastically, and making it ill-suited for this species.

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Conservation Actions

No specific conservation actions have been identified with regards to this species at this time, and no specific research is needed with regards to this species.

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Use and Trade

No use/trade known.

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Source and Citation

Siegel, N. 2022. Lactarius crassus. The IUCN Red List of Threatened Species 2022: e.T198478341A198488648. https://dx.doi.org/10.2305/IUCN.UK.2022-1.RLTS.T198478341A198488648.en .Accessed on 4 August 2023

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