Toxic Fungi of Western North America

by Thomas J. Duffy, MD

General description and occurrence

Muscarine poisoning occurs primarily in the genera Clitocybe and Inocybe. The genus Clitocybe has white spores and white or pale-colored gills that are bluntly attached or run down the stipe. The caps are convex, plane or centrally depressed. The species of Clitocybe considered here are ± white. (148)

Widely occurring Clitocybe species in Western North America reported to contain muscarine are Clitocybe dealbata (Fries) Kummer subspecies sudorifica (Peck) Bigelow, Clitocybe cerussata (Fr.), possibly Clitocybe dilatata Pers. ex Karsten and species apparently close to the European Clitocybe gibba and Clitocybe rivulosa (125) Dr. Bigelow in his North American Species of Clitocybe Part I considers Clitocybe gibba (Fr.) Kummer and Clitocybe rivulosa (Fr.) Kummer to be species close to or identical with Clitocybe catina (Fr) Quélet and Clitocybe splendoides Bigelow respectively. In addition, many Clitocybes contain smaller or variable amounts of muscarine and the various assays do not always agree.

Clitocybe dealbata
Clitocybe dealbata photo © Fred Stevens

The genus Inocybe tends to have small conic to bell-shaped caps that are often brown or display rather pallid colors. The caps are also typically radially fibrillose, splitting or scaly and less commonly smooth. The margin may be lacerated in some of the older specimens. The gill edges are finely fringed in some species (most easily seen under a strong hand lens such as the Hastings Triplet). There is a fine web-like partial veil seen in young specimens, which disappears at maturity, but often leaves a roughened area on the stipe. If a ring is present it is fibrillose and often incomplete. Often the upper portion of the stipe is white and finely stippled. Odors of Inocybe species are often peculiar—earthy, spermatic, fruity or like corn silk. The spore print is a dull brown to dull yellow brown, often “rusty brown”.

Because of the studious work of Malone and others on specimens identified by Dr. Daniel Stuntz (Washington), the list of western muscarinic inocybes is quite long. (149,150 ) Toxic species that occur in California include Inocybe albodisca, I. decipientoides, I. fastigiata (= I. rimosa), I. geophylla, I. kauffmanii, I. lacera, I. lilacina (= I. geophylla var. lilacina), I. mixtilis, I. olympiana, I. pudica (= I. whitei), I. pyriodora (= I. fraudans), I. sororia and I. subdestricta. At least four toxic Inocybes species are found in Mexico: Inocybes fastigiata, I. geophylla, I. lacera and I. lilacina. (26) Pacific Northwest species include the additional species of Inocybe cinnamomea, I. gausapata, I. griseolilacina, I. napipes, I. nigrescens, I. oblectabilis, I. obscuroides, I. picrosma, I. praetervisa, I. terrifera and I. xanthomelas. Almost all of these species extend eastwards to Colorado and the southern Rocky Mountains.

Inocybe geophylla  var. lilacina
Inocybe geophylla var. lilacina photo © Fred Stevens

The most common muscarine poisoning in California, however, appears to be that caused by Boletus satanas. Possible muscarinic symptoms with this bolete have been reported most years in California's Grass Valley and in other Sierra Nevada foothill areas. However, no members of the MSSF toxicology committee have confirmed the presence of SLUDGE. Lillian Mott, a long-time member of the MSSF, described possible muscarinic symptoms in one patient. (151) This large bolete has a massive bulbous stipe and red pores on the undersurface that blue with injury. Some people eat Boletus satanas with impunity. It appears that at least the GI symptoms are avoided by careful cooking.

Boletus satanas
Boletus satanas photo © Michael Wood

Stadelmann and his co-workers noted that muscarine is present in Boletus calopus and Boletus luridus, but only in small amounts. (152) Muscarine presumably is present in Boletus pulcherrimus. (24) Boletus pulcherrimus produced what appeared to be muscarine poisoning in at least one report. (153) Boletus haematinus has not been studied and is readily confused with either Boletus pulcherrimus or Boletus satanas. These large red-pored boletes and similar species should be avoided. Dr. Thier’s California Mushrooms—A Field Guide to the Boletes (California Boletes on this web site) gives good descriptions of Boletus calopus var. frustosis (our Western species) and Boletus erythropus. (154) Boletus calopus var. frustosus usually has red on the cap or stipe and has ± yellow tubes bruising blue; it may be a different species from the European Boletus calopus and may or may not contain muscarine.

Mycena pura, a delicate gilled mushroom which is widespread in North America and can cause gastrointestinal upsets, may also contain muscarine. Omphalotus olivascens, a large dingy yellow-green fungus, which grows in shelves on senescent western trees and stumps, apparently contains muscarine, although it usually causes only gastrointestinal symptoms. Panellus serotina, a common small greenish-yellow to somewhat purplish shelving species also clusters on dead wood. European authors report that their specimens contain muscarine. (56d)