<i>Squamanita contortipes</i>, the Rosetta Stone of a mycoparasitic agaric genus

Fungal biodiversity studies on the Olympic peninsula, Washington, have uncovered the key to understanding one of the most enigmatic mushroom genera worldwide. Discovery of a mushroom (Squamanita contortipes) on another grossly distorted but identifiable agaric (Galerina sp.), which retained partial fertility and morphology, provides documentation of parasitism and gall formation by the genus Squamanita. This revelation leads to a reinterpretation of all Squamanitas as commingled hosts and parasites and supplies a simple explanation for anatomical mixtures of tissues erroneously cited as evidence linking the Agaricaceae, Tricholomataceae, and Amanitaceae. It also resolves six decades of controversy over the identity or function of enlarged bases that often bear chlamydospores. Parasitism of mushroom fruit bodies by other mushrooms is a rare phenomenon (&lt; 20 reported species globally). With the addition of accepted Squamanita species, the number of known sporophorous parasitic agarics worldwide is increased by one-third and the number of obligate mycoparasitic mushroom genera is doubled. Key words: biodiversity, gall, taxonomy, biology, terminology, chlamydospores, Pacific Northwest, Asterophora.