The genus Clostridium was proposed in 1880 by Prazrnowski with the type species C.butryicum,subsequently the genus became a general depository for Gram-positive staining,sporeforming,anaerobic organisms.Consequently,the genus aspresently constituted is phylogenetically and phenotypically incoherent;biochemical,chemical and molecular data indicate that the genus comprises a collection of very heterogeneous species.Presently there are 228 validly published Clostridium species and subspecies with frequent new additions.Numerous phylogenetic studies based principally on sequencing of the 16S rRNA gene,but supported by protein signatures,indicate that the genus Clostridium should be restricted to Clostridium rRNA cluster Ⅰ as Clostridium sensu stricto.Despite this evidence,authors continue to name organisms as Clostridium thus further perpetuating the confusion associated with the taxonomy of this important group of organisms.Furthermore,members of Anaerobacter,Eubacterium,Sarcina,Eubacterium and Sarcina also fall within the radiation of rRNA cluster Ⅰ.A discussion will be presented on the formal proposal to restrict Clostridium to the type species Clostridium butyricum and relatives and the implications for the scientific and clinical community.