Phlebiopsis pilatii (Parmasto) Spirin & Miettinen

Miettinen, Otto, Spirin, Viacheslav, Vlasak, Josef, Rivoire, Bernard, Stenroos, Soili & Hibbett, David S., 2016, Polypores and genus concepts in Phanerochaetaceae (Polyporales, Basidiomycota), MycoKeys 17, pp. 1-46 : 20

Phlebiopsis pilatii (Parmasto) Spirin & Miettinen comb. nov.

Laeticorticium pilatii Parmasto, Eesti NSV Teaduste Akadeemia Toimetised 14(2): 228 (1965)

Remarks.

Phlebiopsis is typified by Phlebiopsis gigantea , a phlebioid species with agglutinated lower subiculum, well-developed basal layer/upper subiculum, thick-walled, simple-septate hyphae and thick-walled, conical, encrusted cystidia (lamprocystidia). Our wider concept of Phlebiopsis dilutes this set of characters, but lamprocystidia, interwoven subhymenium and tightly built subiculum remain as important characters for genus delimitation against similar genera of the Phanerochaetaceae (Table 1).

Hjortstamia crassa has been shown to be a close relative of Phlebiopsis , and has been included in that genus ( Floudas and Hibbett 2015). We agree with this conclusion. The type species of Hjortstamia ( Hjortstamia friesii ) has not been sequenced, but it is very similar to Hjortstamia crassa . Thus Hjortstamia should for now be considered as a taxonomic synonym of Phlebiopsis . In addition to the above-mentioned Hjortstamia spp., a third similar species, Hjortstamia papyrina , is combined to Phlebiopsis on morphological grounds.

The two main differences that have been emphasized to separate Hjortstamia from Phlebiopsis are reflexed basidiocarps and the loose subiculum of the former as opposed to the dense, agglutinated subiculum and totally effused basidiocarps of the latter. A closer look reveals that the difference is not as striking as often described. Whereas the genus type of Hjortstamia - Hjortstamia friesii - and its close relative Hjortstamia papyrina are distinctly pileate, basidiocarps of Hjortstamia crassa are much of the time fully resupinate or caps are small. Hjortstamia crassa also has an agglutinated upper subiculum or basal layer similar to agglutinated Phlebiopsis structures, as depicted by Wu and Chen (1992). Hjortstamia friesii has a tight (though not agglutinated) subicular layer composed of parallel hyphae as well ( Hjortstam and Ryvarden 1989, Boidin and Gilles 2002). Subicular/cystidial hyphae of the above-mentioned species are strikingly similar, thick-walled, straight, stiff and sparsely septate.

A loose subiculum or pileate fruiting bodies do not seem to be useful characters separating Hjortstamia from Phlebiopsis , since loose and agglutinated species are widely intermixed phylogenetically within Phlebiopsis sensu lato (Figure 2). Hjortstamia crassa for instance is more closely related to the type species of Phlebiopsis than is Phlebiopsis flavidoalba with a very dense structure and effused fruiting bodies.

Sequences made available by Wu et al. (2010) include Phanerochaete brunneocystidiata and Phanerochaete laxa . The former is based on a paratype and the latter on the holotype. Wu combined the species in Hjortstamia due to sequence similarity to Hjortstamia crassa . We haven’t seen authentic material, but according to original descriptions, they seem to share basic Phlebiopsis characters except that no agglutinated layer was described ( Wu 2000, 2004).

Some Phlebiopsis species may turn out to belong to the Hapalopilus - Rhizochaete subclade instead of the Phlebiopsis subclade. For instance Phlebiopsis roumeguerei is nested within Phaeophlebiopsis as defined by Floudas and Hibbett (2015). More in-depth research is needed to settle genus classification for Rhizochaete and Phaeophlebiopsis -like taxa.