Toxic Fungi of Western North America

by Thomas J. Duffy, MD

Description and habitat of Amanita phalloides and Amanita ocreata

These two amanitas have caused all of the recorded deaths in California and most of those in the West. The majority of these were patients who had ingested Amanita phalloides. In their button stages, amanitas look like puffballs due to their enclosure in a universal veil, which surrounds the embryonic cap and stipe. As the mushroom matures and the cap expands, this veil is broken and usually leaves remnants on the cap in addition to those universal veil remains at the base of the stipe. The basal remnants are referred to as a volva if ± cup-like. The veil tissue in some species tears into voval rings or mealy basal patches. These volval structures may be fragile and, with careless collecting, left behind in the soil. If the mushroom is pulled up, rather than dug up, even a well-formed volva may be left in the earth. A partial veil from the cap edge to the stipe often leaves a ± persistent ring on the upper portion of the stipe. Amanita phalloides and Amanita ocreata have rather well-formed sac-like volvas and annular rings; both may collapse on the stipe.

Amanita phalloides usually has a large cap (6 to 15 cm across) with no or only faint striations at the edge of the cap. The cap color varies from olivaceous or greenish brown to a brassy yellow brown, at times fading to dingy yellowish or buff in the presence of sunlight. The surface is slightly to moderately tacky when moist. As the mushroom expands beyond the button stage, the cap breaks the outer or universal veil, leaving a thin white volva at the base and a few thin white patches on the cap. Sometimes there are no veil remnants on the cap. The gills, stipe and volva are also white. The gills of mature specimens are free i.e. they do not extend all the way to the stipe. The gills are fairly close together. The length of the stipe approximates or somewhat exceeds the cap width, giving a somewhat stately appearance to the mushroom. The thin cup or sac-like free-margined volva may not be seen, unless the whole specimen is dug up. The volva oftens collapses on the stipe. A white secondary veil protects the young gills on the underside of the cap. When this partial veil breaks, it leaves a thin ± membranous ring on the stipe. This veil remnant atrophies or disappears with aging.

Amanita phalloides
Amanita phalloides photo © Michael Wood

Specimens of Amanita phalloides exposed to sunlight often bleach and appear yellowish or almost white at times. Some collections in drying fade to a dingy yellow, before becoming buff or almost white (usually having a slight sheen). However, a white color variant of Amanita phalloides is completely white from the start. The species then looks like Amanita ocreata. Suggestions that a specimen is not Amanita ocreata, but rather a pallid Amanita phalloides are: very large specimens with caps over 12 cm., occurrence with typical specimens, lack of any warm tan or brown tints on mature caps and fruiting prior to January. Sulfuric acid turns the gills of Amanita phalloides vinaceous to purple, but other amatoxic amanitas show either no change or a pink coloration. Potassium hydroxide solution dropped on to the flesh of Amanita phalloides shows no change in color; but dropped on to the flesh of Amanita ocreata the solution produces a bright yellow color.

The raw flesh of the Amanita phalloides “death cap” is sweet or very slightly acrid and cooked it is quite tasty. (15) There is no odor in the very early stages, but for a brief time, it has an odd slightly floral honeyed odor (not totally pleasant) which deteriorates rapidly to an earthy odor and then to a ghastly “rotting potato” odor. (21) Some coastal State Parks near San Francisco have had hundreds of A. phalloides in an area probably less than an acre. At such a rare mass fruiting, the whole area smells somewhat sweet yet distinctly unpleasant. Moser describes the early odor as “honey-like” in European specimens (22) and Oudot as a withered rose (“rose fanée”). (15) Bon also describes the early odor of A. phalloides as “smell faint, then a little unpleasant, like a rose drying”. (23) This feature is not specific to amatoxin-containing species, however, since other potato stinkers include the innocuous Amanita brunnescens, A. citrina and A. porphyria.

The fruiting bodies of Amanita phalloides most commonly appear from September to March. However, spring and summer fruiting occur sporadically in irrigated areas. The mycorrhizal associate for Amanita phalloides is principally oak, but other trees occasionally act as mycorrhizal host. Additional hosts In the Pacific Northwest (PNW) include filbert and chestnut trees. The association with old orchards suggests the mycelia were brought over from Europe on the roots of various nut trees. (9) One collection in Washington was made near planted juniper and dogwood. (10) The distribution of Amanita phalloides now extends into British Columbia to the north and to San Diego, California to the south. It would be expected in Tijuana, Mexico just across the U.S. border.

Over the past 40 years, this species has thrived in years with heavy fog and wet fall weather along the Pacific coast. Amanita phalloides has spread gradually from its first sightings in the San Francisco Bay Area. It is now common at least 100 miles north and south along the California coast. Collections in Southern California are scattered. Although uncommon in mountain areas, specimens have been found in Granite Bay (Placer County) and near Sutter Creek in Amador County, California. (8) Amanita phalloides also occurs in Oregon, Washington and British Columbia, but Amanita phalloides introduction there and in Southern California are presumably from separate importations.

Amanita ocreata, the native coastal species (California, Oregon, southern Washington and Baja California, Mexico), is just as deadly as Amanita phalloides. The cap is 5-12 cm broad with a stipe 6-20 cm long: slightly smaller on the average than Amanita phalloides. The color of the cap is white at first, but ages buff-colored and tends to discolor a light warm brown or pinkish over the apex. There are no or only faint striations at the edge of the cap. The surface is moist to somewhat tacky when young. It may or may not display thin patches or wisps of universal veil tissue. Gills, ring, stipe and volva are white. The ring collapses early and may disappear. As in Amanita phalloides, the volva is thin, rather sac-like and soon collapses on the stipe. On average, the size is slightly less than that of Amanita phalloides.

Amanita ocreata
Amanita ocreata photo © Michael Wood

Looking much like the white variant of Amanita phalloides, Amanita ocreata fruits most commonly in late January, February, March and early April in California. The prime fruiting time in Oregon and Washington is May. It was thought to be endemic to California, but its range probably extends from the Canadian to the Baja, California border. Although Charles Peck first described Amanita ocreata in 1909, it was not until 1976 that the occurrence of amanitins was documented. (5),(24)

Amanita ocreata has a rare salmon-colored form. (20) This aberrant color may possibly be due to a parasite. This color variant of Amanita ocreata could be confused with the edible Amanita velosa, especially since both species may be fruiting at the same time in the spring.

In California, Amanita ocreata is usually associated with coastal live oak, but it also occurs near or under old deciduous oaks. In Oregon and Washington, it often fruits in the spring after the low-land morel season along rivers, often in silt, but not in recently flooded areas. (9) North of the Columbia River it is commonly associated with filbert. The Hudson’s Bay Company first introduced nut trees into the Vancouver, Washington area before 1840. There has been over 150 years for these nut trees to become an established part of the woodland flora in southern Washington.