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Cercopemyces crocodilinus

[ Basidiomycota > Agaricales > Tricholomataceae > Cercopemyces . . . ]

by Michael Kuo

This recently described, apparently rare species is a denizen of western North America, where it is associated with mountain mahogany—shrub-like trees in the genus Cercocarpus, including birchleaf mountain mahogany, which is what the illustrated and described collection was growing under in Larimer County, Colorado.

Cercopemyces crocodilinus is reminiscent of some species of Amanita; it is a fairly large mushroom with a convex cap that is covered with scales that look very much like the warts on some Amanita species—but the "warts" cannot be easily removed from the cap surface, and are actually innate scales. The stem is also Amanita-like, with its large basal bulb, ringed with veil tissue. However, the gills of Cercopemyces crocodilinus are notched or narrowly attached to the stem, and its microscopic features are not very Amanita-like. In fact Cercopemyces crocodilinus is more closely related to species of Ripartitella (see Ripartitella brasiliensis) and to cystodermatoid mushrooms than to Amanita, according to its DNA (Baroni and collaborators 2014).

Surprisingly, given how large and distinctive it is, Cercopemyces crocodilinus is known from only a few collections in Utah Colorado, and Montana. Have you seen something that looks like it, growing under mountain mahogany? Please send me an email at ; your collection should be preserved and documented!

Thanks to the Sam Mitchel Herbarium of Fungi at the Denver Botanic Gardens for facilitating my study of the Cercopemyces crocodilinus collection cited and described below, and to Ed Lubow for permission to reproduce his photo of the collection.


Ecology: Associated with mountain mahogany (trees in the genus Cercocarpus, including birchleaf mountain mahogany), presumably in a mycorrhizal relationship; growing gregariously; summer; Utah and Colorado. The illustrated and described collection is from Larimer County, Colorado.

Cap: 4–10 cm across; broadly convex; dry; dull yellowish to whitish; covered with innate scales that are larger in the center and smaller toward the margin; the margin adorned with small overhanging scales, and not becoming lined at maturity.

Gills: Narrowly attached to the stem, or notched; close or nearly crowded; short-gills frequent; white.

Stem: 4–6 cm long; 2–3 cm thick; with a large basal bulb that takes up a third to half of the stem's length, creating a squatty stature; dry; whitish; upper edge of the bulb girdled with small white scales.

Flesh: White; not changing when sliced.

Odor: Not distinctive.

Spore Print: Not recorded; presumably white.

Microscopic Features: Spores 4–6 x 3–4 µm; ellipsoid, with a prominent apiculus; smooth; inamyloid; hyaline in KOH; walls cyanophilic in lactophenol and cotton blue. Basidia 2- and 4-sterigmate. Hymenial cystidia not found. Lamellar trama parallel. Pileipellis a cutis; elements 5–7.5 µm wide, smooth, hyaline to yellowish in KOH; with areas of inflated, exserted cells 5–15 µm wide, smooth, hyaline in KOH, with widely cylindric, subclavate, clavate, or subcapitate terminal elements. Clamp connections present.

REFERENCES: T. J. Baroni, B. R. Kropp & V. S. Evenson, 2014. (Baroni et al., 2014; Cripps, Evenson & Kuo, 2016.) Herb. DBG 24386.

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Cercopemyces crocodilinus

Cercopemyces crocodilinus

Cercopemyces crocodilinus
Pileipellis: swollen terminal cell with clamp connection

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Kuo, M. (2018, November). Cercopemyces crocodilinus. Retrieved from the MushroomExpert.Com Web site: