The original description of Xanthoria poeltii S. Y. Kondr. & Kärnefelt was based on morphological and anatomical characters (Kondratyuk & Kärnefelt Reference Kondratyuk and Kärnefelt1997). The new species was reported from a few European localities from Hungary to southern Sweden (Kondratyuk & Kärnefelt Reference Kondratyuk and Kärnefelt1997). The authors provided detailed information on how the new species was distinguished from the other European species in the Xanthoria candelaria group (Poelt & Petutschnig Reference Poelt and Petutschnig1992a , Reference Poelt and Petutschnig b ), viz. X. borealis R. Sant. & Poelt, X. candelaria (L.) Th. Fr., X. fallax (Hepp) Arnold, X. fulva (Hoffm.) Poelt & Petutschnig, and X. ulophyllodes Räsänen.

However, when Kondratyuk & Kärnefelt (Reference Kondratyuk and Kärnefelt1997) described X. poeltii they were apparently unaware of the species X. oregana Gyeln., which was described from Oregon, USA, over 60 years earlier (Gyelnik Reference Gyelnik1934). Thus, they did not compare X. poeltii and X. oregana and discover the similarities between the two taxa. Shortly after the publication of X. poeltii, in a taxonomic revision of the genus Xanthoria, the species X. oregana was resurrected with a description that revealed it to be morphologically identical to X. poeltii (Lindblom Reference Lindblom1997). Both species were later transferred to the genus Xanthomendoza (Søchting et al. Reference Søchting, Kärnefelt and Kondratyuk2002). The currently accepted circumscription of Xanthomendoza includes 15 to 20 mainly foliose species. This genus is mainly characterized by true rhizines and bacilliform conidia (Arup et al. Reference Arup, Søchting and Frödén2013).

Lindblom (Reference Lindblom2006) noted that morphological characters indicated that X. oregana may be closely related to X. poeltii, but avoided explicitly formulating her hypothesis that they are conspecific. Hence, it is interesting to note that in subsequent molecular phylogenetic analyses by Arup et al. (Reference Arup, Søchting and Frödén2013) and Leavitt et al. (Reference Leavitt, Lumbsch and St Clair2013), which included both taxa, they are recovered intermixed in a single well-supported monophyletic clade. Results from these phylogenetic analyses and the lack of diagnostic morphological characters show that there are no character traits that can justify maintaining the taxa as separate, apart from their being distributed in two widely separate geographical areas of the world. Our conclusion is that X. poeltii should be treated as a synonym of X. oregana.

To provide a DNA sequence for identifying the species (Schoch et al. Reference Schoch, Seifert, Huhndorf, Robert, Spouge, Levesque, Chen, Bolchacova, Voigt and Crous2012), we collapsed existing ITS (ITS1-5.8S-ITS2) sequences of X. oregana and X. poeltii using the TCS v. 1.21 software (Clement et al. Reference Clement, Posada and Crandall2000). All seven ITS sequences in GenBank labelled X. oregana and X. poeltii were downloaded (GenBank nos. AM697875, AM697876, AY081158, EU681361, JQ301689, KC179141, KC179142). We considered the specimens from which the sequences had been obtained as reliably determined by experts in the group (see Søchting et al. Reference Søchting, Kärnefelt and Kondratyuk2002; Fedorenko et al. Reference Fedorenko, Stenroos, Thell, Kärnefelt and Kondratyuk2009; Gaya et al. Reference Gaya, Högnabba, Holguin, Molnar, Fernández-Brime, Stenroos, Arup, Søchting, van den Boom and Lücking2012; Arup et al. Reference Arup, Søchting and Frödén2013). We added one additional X. poeltii ITS sequence generated following the methods of Lindblom & Ekman (Reference Lindblom and Ekman2005) [GenBank no KJ396108: Norway, Østfold, Aremark, Rive søndre, UTM(ED50): PL 518 736 (M711: 2013 IV), Alt.: 120 m, På spisslønn i gårdstun, 1998.05.10, Løfall, Bjørn Petter bpl-L3678 – Det. Lindblom, L. 2002 <Merk: LL: DNA extraction 399> (Hb. O-L-35242)]. Both ends were trimmed to remove stretches with ambiguous nucleotides, which resulted in an alignment of c. 330 bp. Sequences were collapsed into only two haplotypes, which are separated by a single point mutation (a transversion in ITS1). The first haplotype includes four sequences: three from specimens identified as X. oregana and one from a specimen representing X. poeltii (Table 1). The second haplotype includes sequences from four specimens of X. poeltii (Table 1). In addition to aiding in molecular identification of the species using the ITS barcode marker (Schoch et al. Reference Schoch, Seifert, Huhndorf, Robert, Spouge, Levesque, Chen, Bolchacova, Voigt and Crous2012), the results corroborate previous studies indicating that X. oregana and X. poeltii are conspecific (Arup et al. Reference Arup, Søchting and Frödén2013; Leavitt et al. Reference Leavitt, Lumbsch and St Clair2013).

Table 1. DNA barcoding of Xanthomendoza oregana. The two haplotypes are separated by one point mutation (a transversion in ITS1, position 176 in our alignment).

Xanthomendoza oregana (Gyeln.) Søchting, Kärnefelt & S. Y. Kondr.

Mitt. Inst. Allg. Bot. Hamburg 30–32: 237 (2002).—Xanthoria oregana Gyeln., Ann. Mus. Nat. Hungarici 28: 284 (1934); type: USA, Oregon, Corvallis, on maple, 1932, Sipe 654 (BP!—holotype).

Xanthoria poeltii S. Y. Kondr. & Kärnefelt, Lichenologist 29: 425 (1997)—Xanthomendoza poeltii (S. Y. Kondr. & Kärnefelt) Søchting et al., Mitt. Inst. Allg. Bot. Hamburg 30–32: 237 (2002); type: Sweden, Skáne, Lund, S. Sandby par., Eliselund, on Ulmus sp., 1995, Kondratyuk (LD!—holotype).

(Fig. 1A–D)

Fig. 1. A–D, Xanthomendoza oregana. A, Canada, British Columbia, southern Vancouver Island, near Victoria; B, Sweden, Skåne, Vomb, Arup & Ekman (LD-1034601); C, Sweden, Skåne, S. Sandby, Kondratyuk (LD-1008720, isotype); D, USA, Washington, Spokane County, Little Spokane River Natural Area. Photographs A & D, C. Björk; B & C, E. Timdal. In colour online.

Diagnostic features of X. oregana are the bright yellow colour of the upper cortex, loosely adpressed to ascending lobes that are smooth or sometimes slightly wrinkled, and developing marginal to submarginal blastidia. Apothecia are rare, though abundant on some individual specimens. Pycnidia are frequently present, and usually contain conidia that vary in shape from ellipsoid to bacilliform (cf. Lindblom Reference Lindblom1997, Fig. 3C; Søchting et al. Reference Søchting, Kärnefelt and Kondratyuk2002). Secondary chemistry: chemosyndrome A (sensu Søchting Reference Søchting1997).

More information on characters of Xanthomendoza oregana and how it is distinguished from other morphologically similar species, for example X. candelaria and X. fulva, is found in the original description (Kondratyuk & Kärnefelt Reference Kondratyuk and Kärnefelt1997: 429) as well as in later descriptions and keys by Lindblom (Reference Lindblom1997, Reference Lindblom, Nash, Ryan, Diederich, Gries and Bungartz2004, Reference Lindblom2006).

Xanthomendoza oregana in this sense belongs to the western Europe–western North America disjunct biogeographical element (Schofield Reference Schofield1969, Reference Schofield1988; Nash Reference Nash2008). In western North America it is widespread in the Pacific oceanic and suboceanic areas (Lindblom Reference Lindblom2006). In Europe it has been reported (as X. poeltii) from Hungary (Kondratyuk & Kärnefelt Reference Kondratyuk and Kärnefelt1997), Germany (Wirth et al. Reference Wirth, Hauck and Schultz2013, as Gallowayiella poeltii), Denmark (Søchting & Alstrup Reference Søchting and Alstrup2008), southern Sweden, and southern Norway (Nordin et al. Reference Nordin, Moberg, Tønsberg, Vitikainen, Dalsätt, Myrdal, Snitting and Ekman2014). However, its geographical distribution is still incompletely known. Notably, X. oregana seems to differ from most lichens and bryophytes of this disjunct element in being a species of lowland temperate areas (cf. Schofield Reference Schofield1988; Nash Reference Nash2008). Xanthomendoza oregana grows on deciduous trees in open sites. In southern Sweden it is frequent on trees in parks and churchyards.

A comprehensive revision including phylogenetic investigation integrating molecular and morphological characters of the species in the genus Xanthomendoza is much needed, as has previously been pointed out (Lindblom Reference Lindblom2006).