• Proposed
  • 2Under Assessment
  • 3Preliminary Assessed
  • 4Assessed
  • 5Published

Lactarius crassus (Singer & A.H. Sm.) Pierotti

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Scientific name
Lactarius crassus
(Singer & A.H. Sm.) Pierotti
Common names
IUCN Specialist Group
Mushroom, Bracket and Puffball
Assessment status
Proposed by
Noah Siegel
Comments etc.
Noah Siegel

Assessment Notes

Taxonomic notes

Described as Arcangeliella crassa from a collection made in Stanislaus National Forest, California, USA (Singer & Smith, 1960). Thiers (1979) considered Arcangeliella tenax a distinct species; further study (Thiers, 1984) referenced the considerable overlapping in the characters used to separate Arcangeliella crassa from A. tenax, (described from Mount Hood, in Oregon) considered them synonyms. 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.

Why suggested for a Global Red List Assessment?

Lactarius crassus is a sequestrate species of Lactarius which occurrs in higher elevation fir forest in the Sierra Nevada, southern Cascade and Klamath Ranges, with ~25 known locations.
Recognized by the medium size (larger than other montane ‘Arcangeliella’ species), pinkish buff colors, a gleba which is often obscured by a peridium when young, and a strongly acrid taste. Fresh fruitbodies exude white latex when cut, older or drier fruitbodies often lack latex.

Geographic range

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.

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, USFS) found a number of collections from 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. It is uncommon in the California mountains, but not enough data is available to show positive nor a negative population trend. It is possible, with the trend of more fir (Abies) dominated forests in the Sierra Nevada, populations are improving.

Population Trend: Stable

Habitat and Ecology

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


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 understory burns) are commonplace, altering appropriate habitat drastically, and making it ill-suited for this species.

Conservation Actions

Research needed

Use and Trade


Kirk, P.M. 2015. Index Fungorum 278: 1.

Singer, R, and Smith, A.H. 1960. Studies on secotiaceous fungi. IX. The astrogastraceous series. Memoirs of the Torrey Botanical Club 21(3):1–112.

Smith, A.H. 1963. New astrogastraceous fungi from the Pacific Northwest. Mycologia 55: 421–441.

Siegel, N., Vellinga, E.C., Schwarz, C., Castellano, M.A. and Ikeda, D. 2019. A Field Guide to the Rare Fungi of California’s National Forests. Bookmobile: Minneapolis, MN. 313 p.

Thiers, H.D. 1984. The genus Arcangeliella Cav. in the western United States. Sydowia 37:296–308.

Vidal, J.M. 2005. Arcangeliella borziana and A. stephensi, two gasteroid fungi often mistaken. A taxonomic revision of Lactarius-related sequestrate fungi. Revista Catalana de Micologia 26:59–82.

Mushroom Observer. http://www.mushroomobserver.org

MyCoPortal. Mycology Collections Portal. Available at: http://mycoportal.org

Country occurrence

Regional Population and Trends

Country Trend Redlisted