Cortinarius is the most species rich genus of the Agaricales with a worldwide distribution. Cortinarius species are important ectomycorrhizal fungi associated with different trees and shrubs belonging e.g. to the order Fagales and families Pinaceae and Salicaceae. Lately it has also been suggested that they have a key role in the carbon cycling of boreal forests (Bödeker et al. 2011).

In recent years there have been a number of publications on the taxonomy, evolution and biogeography of species found in North America (Seidl 2000, Moser and Peintner 2002, Matheny and Ammirati 2006, Garnica et al. 2009, 2011, Bojantchev 2011a, b, Bojantchev and Davis 2011, Harrower et al. 2011, Ammirati et al. 2012, 2013, Niskanen et al. 2012, 2013a, in press a). These studies show several patterns of species distributions. There are species common to North America and Europe, especially those species from more northern and montane conifer forests, i.e. Cortinarius aureofulvus M. M. Moser and Cortinarius napus Fr. There are also presumably endemic species in both Western North America, eastern North America and Europe, i.e. Cortinarius elegantio-occidentalis Garnica & Ammirati and Cortinarius californicus A.H. Sm. in western North America, Cortinarius hesleri Ammirati, Niskanen, Liimat. & Matheny in eastern North America, and Cortinarius puniceus P.D. Orton in Europe.

Niskanen et al. (in press b) studied Cortinarius bovinus Fr. and morphologically similar species occurring in boreal coniferous forests in rich forest soils in northern Europe. Seven species were recognized, all belonging to section Bovini (subgenus Telamonia). Four of them, Cortinarius bovinus Fr., Cortinarius bovinaster Niskanen, Kytöv. & Liimat., Cortinarius bovinatus Kytöv., Liimat., Niskanen & H. Lindstr., and Cortinarius oulankaënsis Kytöv., Niskanen, Liimat. & H. Lindstr., formed a well-supported (PP 1.00) clade inside sect. Bovini (Bovini s. str.). The species are characterized by brown to dark brown basidiomes without bluish colors and exsiccatae with a dark brown to blackish brown pileus. The universal veil is white, brownish white or grayish white, in some species becoming grayish brown with age, and the odor is indistinct or slightly raphanoid. To date, species are only known from Europe, except Cortinarius oulankaënsis which also occurs in Canada in British Columbia. By studying more material from western North America, we wanted to determine if Cortinarius bovinus found from Alaska, U.S.A. and Alberta, Canada is conspecific with European samples or does it represent an autonomous species.

Material gathered by the authors from North America was studied morphologically, ecologically and sequenced to infer phylogentic relationships with other species in Bovini. DNA was extracted from dried material (a piece of lamella) with the NucleoSpin Plant kit (Macherey-Nagel, Düren, Germany). Primers ITS 1F and ITS 4 (White et al. 1990, Gardes and Bruns 1993) were used to amplify ITS regions, and specific primers cort6F and b7.1R (Frøslev et al. 2005) for the rpb2 region. The same primer pairs were used in direct sequencing. PCR amplification and sequencing followed Niskanen et al. (2009). Sequences were assembled and edited with Sequencher 4.1 (Gene Codes, Ann Arbor, Mich., USA). Using a BLAST query of the public databases (GenBank: http://www.ncbi.nlm.nih.gov/ and UNITE: http://unite.ut.ee/ ), we checked if identical or similar sequences for our species exist in public databases. For the phylogenetic analysis ITS and rpb2 sequences of the species belonging to the well-supported ingroup of section Bovini, Cortinarius bovinus, Cortinarius bovinaster, Cortinarius bovinatus, and Cortinarius oulankaënsis, were included. Cortinarius anisatus, Cortinarius neofurvolaesus, and Cortinarius sordidemaculatus were chosen as outgroup species.

The combined ITS and rpb2 alignment of 11 specimens was produced with the program MUSCLE (Edgar 2004) under default settings. The alignment comprised 1286 nucleotides (including gaps). The alignment is available at TreeBASE under S14159 (http://www.treebase.org/treebase-web/home.html ).

Bayesian inference (BI) was performed with MrBayes 3.1.2 (Ronquist and Huelsenbeck 2003). The best substitution model for the alignment was estimated by both the Akaike information criterion and the Bayesian information criterion with jModelTest version 0.1.1 (Posada 2008). A GTR model, including a gamma shape parameter, was chosen for both DNA regions. Two independent runs with four chains in each were performed for 1 000 000 generations sampling every 100th generation. All trees sampled before stationarity were discarded with a 25% safety margin (burn-in of 2 500 trees [250 000 generations]). Sampled trees from both runs were combined in a 50% majority rule consensus phylogram and posterior probabilities (PP) were calculated. The analysis was run with computer clusters of the CSC, IT Center for Science, Espoo, Finland.

Morphological descriptions are based on material collected by the authors including specimens in all stages of development. Color notations in the description follow Munsell (2009) soil color charts. Microscopic characteristics were observed from dried material mounted in Melzer’s reagent (MLZ). Measurements were made in MLZ with an ocular micrometer using 100× oil-immersion lens. Basidiospores were measured from the veil or top of the stipe, 20 spores from one basidiocarp. The length and width were measured for each spore, and their length/width ratios (Q value) were calculated. The lamellar trama and basidia also were examined, and the pileipellis structure was studied from scalp sections taken from the pileus center.

The 50% majority rule phylogram resulting from the BI analysis is shown in Fig. 1. Cortinarius bovarius is supported as a new taxon (PP 1.00). It clusters together with Cortinarius bovinus (PP 0.90) but differs from it by at least 18 substitutions and indel positions in the ITS regions and 3 substitutions in the rpb2 region. The four ITS sequences of Cortinarius bovarius have altogether 1 base and 2 length intragenomic polymorphisms. No sequences of this species exist in public databases.