Rise up, Rhizoctonia: moving to one fungus, one name in the Ceratobasidiaceae (Agaricomycetes, Cantharellales).

Abstract

Ceratobasidiaceae is a family of cryptic basidiomycetous fungi, most notable for the plant pathogens known under generic names such as Rhizoctonia, Thanatephorus, Ceratorhiza, and Ceratobasidium. While responsible for billions of dollars in crop losses annually, members of these genera also serve important ecological functions as orchid mycorrhizal symbionts and saprotrophs. While asexually-typified (Rhizoctonia and Ceratorhiza) and sexually-typified (Thanatephorus and Ceratobasidium) names have been utilised, molecular studies have repeatedly demonstrated these genera to be paraphyletic. In addition, the type of Ceratobasidium is not congeneric with the many other species introduced in the genus. Despite previous attempts to synonymise various names under a broadly-defined Rhizoctonia, authors have continued to describe new species using outdated generic names. Using publicly-available ITS, LSU, ATP6, RPB2, and TEF1 sequences generated from holotype specimens or from isolates obtained from permanently preserved cultures of type collections (ex-type specimens), we recovered a phylogeny of the Ceratobasidiaceae that reiterates the paraphyly of various genera within a well-supported clade to which we apply the name Rhizoctonia. We review the placements of names introduced in the genera Ceratobasidium, Ceratorhiza, and Thanatephorus, and formalise 32 new combinations in Rhizoctonia. While it is accepted that the type of Ceratobasidium does not belong in Rhizoctonia, we advocate continued use of the family name Ceratobasidiaceae and discuss a nomenclatural solution to formally cement this usage. Using Rhizoctonia as a case study, we argue that continued use of names that are evident synonyms is out of step with contemporary fungal taxonomic practice and precludes a holistic understanding of the classification and biology of this group. Citation: O'Donnell RP, Linde CC, May TW (2025). Rise up, Rhizoctonia: moving to one fungus, one name in the Ceratobasidiaceae (Agaricomycetes, Cantharellales). Persoonia 54: 285-325. doi: 10.3114/persoonia.2025.54.09.