Rhizophlyctis rosea (Chytridiomycota) is an apparently ubiquitous, soil-inhabiting, cellulose-degrading chytrid that is the type for Rhizophlyctis. Previous studies have revealed multiple zoospore subtypes among morphologically indistinguishable isolates in the R. rosea complex sensu Barr. In this study we analysed zoospore ultrastructure and combined nu-rRNA gene sequences (partial LSU and complete ITS1-5.8S-ITS2) of 49 isolates from globally distributed soil samples. Based on molecular monophyly and zoospore ultrastructure, this group of Rhizophlyctis rosea-like isolates is designated as a new order, the Rhizophlyctidales. Within the Rhizophlyctidales are four new families (Rhizophlyctidaceae, Sonoraphlyctidaceae, Arizonaphlyctidaceae, and Borealophlyctidaceae) and three new genera (Sonoraphlyctis, Arizonaphlyctis, and Borealophlyctis).