Unravelling the P hellinus pini s.l. complex in N orth A merica: a multilocus phylogeny and differentiation analysis of P orodaedalea

Phellinus sensu lato (s.l.) is a complex of segregate genera that act as aggressive pathogens of woody plants. Nearly all of the genera in this complex have unresolved taxonomies, including P orodaedalea , which is one of the most important trunk rot pathogens of coniferous trees throughout the northern hemisphere. In an attempt to elucidate the species within P orodaedalea , a multilocus phylogenetic analysis was performed with partial sequences from four loci (internal transcribed spacer, nuclear large subunit, tef1 and rpb2 ) using 41 isolates that originated from N orth A merica and Europe. For reference, we analysed the neotype isolates of P orodaedalea pini and P . chrysoloma . Our results confirmed that P orodaedalea pini s.s. and P . chrysoloma s.s. are unique phylogenetic species that do not occur in N orth A merica. We detected two discrete clades of P orodaedalea originating from the southwestern and southeastern United States. Isolates from these regions grouped with significant statistical support and represent undescribed taxa. With the exception of P . cancriformans , our analyses revealed monophyly among 28 isolates originating from the northern U nited S tates, C anada and F ennoscandia, a group we have labelled the ‘Holarctic group’. Holarctic group isolates were collected from L arix , P icea , P inus , P seudotsuga and T suga and were presumed to represent at least four morphological species ( P . gilbertsonii , P . laricis , P . pini s.l. and P . piceina ). Tests of gene flow and genetic differentiation detected significant differences among H olarctic group isolates by region of origin, and three subgroups were designated: (i) Atlantic‐Boreal; (ii) Interior; and (iii) Pacific. Neutrality tests using the Holarctic group demonstrated significant departures from the standard neutral model of evolution and could indicate that a diversifying selection has maintained rare phenotypes in the population, which has fostered taxonomic confusion in P orodaedalea .