A well resolved phylogeny of the Agaricaceae based on partial rpb2 sequences is presented from a wide geographic and systematic sampling of the family and compared to phylogenies based on nrLSU and tef1 sequences. A smaller dataset of the family focusing on the Agaricus clade of nrITS sequences and a combined dataset were used to determine the position of several white-spored taxa from northern Thailand. Two new genera are described from Thailand. Coniolepiota accommodates Lepiota spongodes, a gray-lilac-purple floccose white-spored species with a wide distribution in tropical Asia; Eriocybe has a white wooly felt-like covering of pileus and stipe, white spores and is described with one new species E. chionea, so far known only from northern Thailand. These new genera are closely related to three genera with colored spores (viz. Agaricus, Heinemannomyces and Clarkeinda) and not to other white-spored taxa.