See http://www.clarku.edu/.... According to this article and some other articles, based on genetic information, the old Volvariella was polyphyletic. Volvopluteus as defined in the article is a relatively small sister genus to Pluteus. Amanita is closer to these two genera than any of them are to the clade containing Volvariella volvacea (the type for Volvariella according to MycoBank). There is no proposal for a higher level taxon for Volvariella in the article, but there is genetic evidence that it’s related to )Cantharocybe gruberi) and )Camarophyllus basidiosus).