Molecular evidence supports the distinction between Xanthoria parietina and X. aureola (Teloschistaceae, lichenized Ascomycota) Louise LINDBLOM and Stefan EKMAN Department of Biology, University of Bergen, Alle´gaten 41, N-5007 Bergen, Norway. E-mail : louise.lindblom@bio.uib.no Received 9 February 2004; accepted 30 October 2004. This study aims to clarify taxonomic relationships within the current concept of Xanthoria parietina in northern Europe. For comparison, X. calcicola was also included in the study. Morphological as well as molecular data were utilized. Morphology indicated the presence of three species, Xanthoria parietina, X. calcicola, and X. aureola, the latter of which is resurrected here from synonymy. The most important separating characters involve colour and thickness of the thallus, lobe width, morphology of laminar structures, and the texture of the upper surface. X. aureola, as recognized here, mostly occurs on seashore rocks. Part of the IGS region as well as the complete ITS were sequenced in 70 individual thalli representing ten geographical regions in Europe. In total, 19 different IGS haplotypes and 20 different ITS haplotypes were present in the data set. Owing to indications of possible recombination between the IGS and the ITS, the two data sets were analyzed separately. Haplotype networks were estimated, both of which indicate that X. parietina is distinct from X. aureola and X. calcicola. In our sample, the two latter do not share haplotypes, but are only separated by a few mutational steps. INTRODUCTION Xanthoria parietina is an easily observed and readily recognized lichenized species, which is exceedingly common in several areas of the world. Yet, it displays a large amount of morphological and ecological variation and this has been interpreted in various ways taxo- nomically. The species was first formally described by Linnaeus (1753 ; as Lichen parietinus). Over the years, the morphological variation attracted attention and several varieties and forms were described and named by early taxonomists (cfr Hillmann 1920). Most authors currently accept a reasonable amount of variation with regard to morphology without necessarily assigning names to morphotypes. There are, however, uncer- tainties concerning some morphological, chemical as well as ecologically seemingly well-defined morphs. These might deserve some taxonomic rank, but in most treatments uncertainties regarding their status have been expressed. X. aureola is an example of a name with unclear taxonomic relationships with X. parietina. It was de- scribed by Acharius (1809; as Parmelia aureola) from seashore rocks in Sweden. Erichsen (1930) combined it into the genus Xanthoria, stating that he considered it a distinct species. He had used the name X. aureola for seashore morphotypes even earlier (Erichsen 1928), and he kept it separate from X. parietina, using both names parallelly. Unfortunately, later authors er- roneously applied the name X. aureola to the taxon that is known since 1984 as X. calcicola (Santesson 1984) (Table 1). The seashore morphotype that Acharius originally recognized as a taxon has later mostly been included within the concept of the variable species X. parietina. The only recent treatments where the sea- shore morphotype is treated separately from X. par- ietina cover Great Britain, Ireland, and Italy (Laundon 1992, Nimis 1993; both as X. ectaneoides). Laundon (1992) added that it had been considered an ecotype of X. parietina and that its status merited further investi- gation. X. aureola, reproducing mainly by fragmen- tation, and X. calcicola, reproducing chiefly by isidia, were interpreted as secondary species derived from the primary species X. parietina (Laundon 1992). Nimis (1993) indicated that it belongs to a poorly understood complex. Neither X. aureola nor X. calcicola seem to be present in North America, but only X. parietina (Degelius 1940, Lindblom 1997). Doubts have been expressed whether the taxa in the X. parietina complex are separated by heritable differences, or, if the ob- served variation just represents effects of environmental modification of the phenotype (Hill & Woolhouse 1966, Richardson 1967). Franc & Ka¨rnefelt (1998) Mycol. Res. 109 (2): 187–199 (February 2005). f The British Mycological Society 187 DOI: 10.1017/S0953756204001790 Printed in the United Kingdom.