Toxic Fungi of Western North America

by Thomas J. Duffy, MD

Identification aids

Visual findings are only part of the gross anatomical features. Texture, odor, taste and surface features such as stickiness, “hairs”, scales and veil patches are very helpful. The edible Marasmius oreades, for example, has a felty texture and pliant tough feel, which is very different from the fragile species that a pot-hunter is also likely to find on lawns. None of the toxic clitocybes e.g. have a velvety pliant cap or a tough stipe that bends so easily without breaking. The spicy odor and the relative toughness of Tricholoma magnivelare ("Matsutake") help distinguish this taxon from the kidney-toxic Amanita smithiana.

Common sense, however, dictates that one should best avoid tasting a mushroom suspected of containing amanitins.

If there is uncertainty about identification, a spore print may help. The stipe is cut off and the cap is placed onto paper with the gills facing down. A glass, cup or saucer is placed over the specimen so that air currents do not waft away the spores. Adding 1-3 drops of water to overly dry caps may help to get a better spore print (usually obtained in 1-4 hours, but may take overnight). Spore prints may be the same as the gill color or differently colored. The author uses white paper and a glass slide to bring out the spore print more clearly.

The use of a slide allows determination of amyloidicity (presence of starch), as determined in the iodine-rich Melzer’s solution. The possibilities are amyloid (grayish blue color), dextrinoid (a reddish brown color) and inamyloid (no color except for the yellow tan of Melzer's solution). The test may be done without a microscope, but weak stains may be misleading. Use of a magnifying glass or microscope is recommended. The high power enlargement of a Hastings triplet is useful in the absence of a microscope.

Confusion in some genera is really due to a lack of attention to the gross anatomy of fungi. Surface features of mushrooms often change with age, usually with loss of color, viscidity and features of any veil or scale elements present. Scales are innate to a cap or stipe; patches that may be wiped away are secondary to partial or universal veils; a partial veil runs from the edge of the cap to the stipe and a universal veil covers the entire fruiting body. A viscid cap in age as it dries, for example, may display only shininess and, if the examiner is lucky, there are "pasted" leaves or debris on the cap. On moistening the cap, a tacky feeling may be felt with the "lip test" (a slight pulling of the lip as the mushroom is removed from it). Mushrooms that are "hygrophanous" have rather thin-fleshed caps that dry a lighter color. Since details tend to be lost in aging, identification is easier if both young and older specimens are examined.