Postia alni Niemelä & Vampola (Basidiomycota, Polyporales) – member of the problematic Postia caesia complex – has been found for the first time in Hungary

Abstract Due to their bluish basidiocarps the Postia caesia (syn. Oligoporus caesius) complex forms a distinctive morphological group within the polypore genus Postia Fr., 1874. Five species of this group occur in Europe: Postia alni Niemelä & Vampola, Postia caesia (Schrad.) P. Karst., Postia luteocaesia (A. David) Jülich, Postia mediterraneocaesia M. Pierre & B. Rivoire and Postia subcaesia (A. David) Jülich. In this study Postia alni is reported for the first time from Hungary. The dichotomous key of the species of the European Postia caesia complex was prepared as well.


Introduction
Postia Fr. is a brown rot polypore genus, which contains annual species with mainly soft, whitish basidiocarps, thin-walled, hyaline spores and monomitic hyphal system with clamped generative hyphae (Jülich 1982). Previously most of the taxa were considered to be members of the genus Tyromyces P. Karst. (e.g. Donk 1960, Jahn 1963, David 1974. However, Jülich (1982) proved that the type (T. chioneus (Fr.) P. Karst.) of Tyromyces P. Karst. is a white rot species. Hence he examined Tyromyces s. l. and found that Postia Fr. Fries, 1874 is the earlier legitimate name of the brown rot P. caesia and P. subcaesia. Ryvarden and Gilbertson combine for the same species into the genus Oligoporus Bref., 1888, based on the opinion, according to which Postia Fr. is a nomen provisorium or nudum of Fries (Gilbertson andRyvarden 1985, Ryvarden andGilbertson 1994). Nevertheless, the solution of Jülich that Postia was validly published by Fries (Fries 1874) was accepted by several mycologists (e.g. Larsen and Lombard 1986, Renvall 1992, Pegler and Saunders 1994. Previous phylogenetic study of Tyromyces s. l. shows that the distinction between Postia and Oligoporus is not significant (Yao et al. 1999). However a recent work shows that the two genera are different and the species of the Postia caesia complex belong to the Postia sensu stricto clade (Ortiz-Santana et al. 2013).
Based on the bluish tints of the basidiocarp and the lack of the chlamydospores in culture, Postia caesia complex forms a distinctive morphological group within the genus (Ţura et al. 2008). Five species of this group occur in Europe. Postia caesia (Schrad.) P. Karst. is a widespread species around the word, which in Europe grows preferably on gymnosperms (Bernicchia 2005, Ryvarden andGilbertson 1994). Postia subcaesia (A. David) Jülich is macroscopically similar, but mainly grows on angiospermic trees and has narrower spores (Ryvarden and Gilbertson 1994). Postia alni Niemelä & Vampola also occurs on deciduous trees, but has smaller basidiocarp and the surface of the pileus is not as hairy as that of the P. subcaesia has ( Fig. 2) (Niemelä et al. 2001). Postia luteocaesia (A. David) Jülich is a rare Central-European species, which grows on Pinus. The main characteristic of this species is the bright yellow color of the basidiocarp besides the blue-grayish discoloration (Niemelä et al. 2004, Ryvarden andGilbertson 1994). From the Mediterranean region P. mediterraneocaesia M. Pierre & B. Rivoire has been described which has spores wider than 1.5 μm as P. caesia and P. luteocaesia (Pieri and Rivoire 2005).
Based on microscopic characters and host preference Postia alni shows a great similarity to P. subcaesia. It differs by the matted pileus surface and the smaller size of the basidiocarp (Niemelä et al. 2001, Piątek 2003. Previously some mycologists (Enderle 1979, Jahn 1963, Vampola 1994) also observed the macroscopical variability of P. subcaesia s. l., but there was not any valid new taxa name published. Velenovsky described a species (Polyporus alni Velen., 1922) which is identical with Postia alni, however it is illegitimate, because it is a later homonym of Polyporus alni Sorokin, 1892. Accordingly, Niemelä and Vampola described the new species under the name Postia alni, retaining the epithet, which was given by Velenovsky (Niemelä et al. 2001).
Previously in Hungary, only two species were known within the Postia caesia complex: P. caesia and P. subcaesia (e.g. Igmándy 1991, Szabó 2012. In this study P. alni is recorded for the first time from Hungary from two locations.

Materials and methods
The basidiocarps (Fig. 3) were collected in Juhdöglő-völgy Forest Reserve (Vértes Mts) and Dobogókő (Visegrádi Mts). Both of them were growing on dead Fagussylvatica. The specimens (PV188, PV977) were placed into the personal collection of the author (PV) and are available at the Botanical Department of Corvinus University of Budapest, Hungary. The identification of the specimens were based on the works of Niemelä et al. (2001) and Piątek (2003). For microscopical studies a Zeiss Axio Imager.A2 light microscope was used. For the measurements a × 1000 magnification objective, oil immersion and the program AxioVision Release 4.8.2 were used. The line drawings of the anatomical characteristics of the basidiocarp (Fig. 1) were made by the author with a drawing tube.
The key of the European Postiacaesia complex was prepared after the following works: Bernicchia (2005)

Discussion
There are many difficulties related to the identification of the species of the Postia caesia complex. There are some confusing East-Asian collection data that cannot be identified as either P. alni or P. subcaesia (Ţura et al. 2008). For instance, Wei and Dai (2006) mentioned Postia alni from China and gave spore size (less than 4 μm) that is different from the European taxa (4.4-6 μm in Niemelä et al. 2001). Molecular data (Yao et al. 2005) showed that the taxonomy of this group is more complicated and further studies are needed for the identification of the species of the complex.