## 4 Discussion
Furthermore, [PERSON] believed that _P. betulinus_ can be further divided into two subspecies: ssp. _betulinus_ from North America and ssp. _orienicus_ from Asia. The results presented here show that _P. laevis_ s.s., _P. betulinus_ and _P. orientcus_ each represent a unique phylogenetic species. While this assertion is supported by only one dataset (_tef_1), prior studies have shown _tef_1 to be the only marker capable of discriminating between very closely-related species in basidiomycete genera like _Armillaria_ and _Trametes_[42, 43, 44]. Additionally, the ITS dataset was able to discriminate _P. orientcus_ from _P. betulinus-P. laevis_ s.s. with a high level of support (BS/PP = 99/1). Thus, the results presented here support the elevation of _P. orientcus_ and _P. betulinus_ to species status. _Phellinus orientcus_ has been previously treated as a distinct species based solely on morphological characters [45]. Additionally, [PERSON] and [PERSON] [8] treated _P. orientcus_ as a unique species in their study to deconstruct _Phellinus_ s.l. using nLSU sequences. In this study, nLSU sequences were unable to discriminate among members of _P. laevis_ s.l. Isolates collected from _Prunus_ in North America that were thought to represent _P. tuberculosus_ were instead shown to be a separate phylogenetic species, referred to here as _P._ NA2. What is perhaps more interesting is that each locus examined in this study showed that _P._ NA2 is more closely-related to _P. tremulae_ than to _P. tuberculosus_. Meanwhile, the results also reveal a close genetic relationship between _P. tuberculosus_ and _P. arctostaphyli_. Regardless of its closest relative, the results suggest that _P. tuberculosus_ is restricted to Europe and Asia and that _P._ NA2 requires formal description as a new North American species. [PERSON] [22] (pp. 64-65) did note that specimens of _P. tuberculosus_ from Europe had larger basidiospores compared to specimens from North America and that: \"The American plant should perhaps be designated as a distinct variety\". Basidiospore variation between _P._ NA2 and _P. tuberculosus_ was also confirmed by [PERSON] [46] and [PERSON] and [PERSON] [5]. The first recognized description of _Phellinus_ from _Prunus_ was performed by [PERSON], who described the species as _Boletus tuberculosis_[47]. This name was soon forgotten though, in favor of the epithet _B. pomaceus_, which appeared in the literature less than a decade later [48]. Both of these early descriptions utilized European strains of the pathogen. Numerous, subsequent descriptions of this species were made in North America and Europe, all using _Phellinus pomaceus_[5, 22, 46, 49, 50] until it was determined to be a synonym of _P. tuberculosis_, with the latter having precedence [51]. After this point, [PERSON] and [PERSON] [52] adopted the use of _P. tuberculosis_ while [PERSON] and [PERSON] [53] preferred use of the well-established _P. pomaceus_. Phylogenetic studies of _Phellinus_ s.l. have consistently used _P. tuberculosis_ over _P. pomaceus_[7, 8, 10, 12], but the use of _P. pomaceus_ still continues, albeit infrequently [54, 55]. Adding to the confusion is the fact that _P. alni_ can also be found on _Prunus_[6] along with _Fomitiporia prunicola_[56]. One of the most fascinating aspects of _Phellinus_ s.s. is that five species are known to occur primarily on _Betula_ (_P. betulinus_, _P. laevigatus_ s.s., _P. lundelli_, _P. nigricans_, and _P. orientcus_). Three of these species (_P. betulinus_, _P. lundelli_ and _P. nigricans_) are present in North American forests and have overlapping host ranges. Not only do these three species occupy the same geographic area but they appear to occupy the same ecological niche, with no apparent preference for a particular species of _Betula_. Clearly, these species represent an interesting model for studies on sympatric speciation. At the same time, _P. nigricans_ and _P. lundelli_ were somewhat partitioned in their distribution in North America, with _P.