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any one of a large group of basidiomycetous mushroom. Gill fungi have a lamellar hymenophore—radially distributed bladelike processes with a hymenium—on the lower side of the cap. The fruiting bodies of most gill fungi are annual and fleshy; less frequently, they are leathery. Some species are edible, including Lactarius deliciosus, Lactarius piperatus, Lactarius torminosus, Russula roseipes, Armillaria mellea, and Psalliota campestris. Toxic gill fungi include Amanita phalloides and Amanita muscaria. Several species destroy live trees and dead wood (A. mellea, Collybia velutipes, and Lentinus lepideus Fr.).
Formerly, all gill fungi were united in the single family Agaricaceae. Many genera have been reclassified and placed in different families, which do not even belong to the same order.