Molecular phylogeny, biogeography and speciation of the mushroom species Pleurotus cystidiosus and allied taxa

Members of the mushroom genus Pleurotus form a heterogeneous group of edible species of high commercial importance. Subgenus Coremiopleurotus includes taxa that produce synnematoid fructifications (anamorphic state). Several species, subspecies and varieties have been described in Coremiopleurotus. These taxa are discriminated by minute morphological differences and correspond to Pleurotus cystidiosus sensu lato. A worldwide geographical sampling of Coremiopleurotus taxa and nucleotide sequence data from the internal transcribed spacer of the nuclear rRNA genes (ITS) were used to produce a molecular phylogeny for the group. Also conducted were new interfertility studies, and a summary of the mating data currently available in the literature is provided. Both ITS phylogeny and mating data supported the distinction between Pleurotus australis (a species apparently endemic to New Zealand and Australia) and P. cystidiosus sensu lato. Within P. cystidiosus sensu lato, ITS phylogeny showed a deep split between Old and New World isolates and clearly distinguished four distinct clades that strongly corresponded to the geographical origin of the strains. In the Old World, one clade is composed of isolates from Europe and Africa, and one clade is composed of isolates from Asia (including collections from Hawaii). In the New World, one clade is restricted to isolates from Mexico, and one clade includes all the authors' North America isolates, one collection from Japan and one collection from South Africa. Mating data revealed a high level of interfertility among strains of P. cystidiosus sensu lato, except that isolates from Mexico were nearly fully intersterile with the other collections. Nucleotide sequence divergence in the ITS1-5(.)8S rDNA-ITS2 regions among intercompatible P. cystidiosus collections was very high (0-6(.)9%) in comparison to that reported in other biological species of basidiomycetes (0-3%), indicating significant genetic divergence between geographically isolated populations of the P. cystidiosus group. The phylogenetic species concept, as well as molecular, mating and geographical evidence, was used to recognize five species in the subgenus Coremiopleurotus: P. australis (in New Zealand and Australia), Pleurotus abalonus (in Asia and Hawaii), Pleurotus fuscosquamulosus (in Africa and Europe), Pleurotus smithii (in Mexico) and Pleurotus cystidiosus sensu stricto (in North America). However, geographical boundaries between these species are not strict, as rare events of long distance dispersal have occurred.