Molecular systematics of Arthrorhaphis with special consideration of the A. alpina ― A. citrinella species complex

Background: Arthrorhaphis Th. Fr. includes c. 11 species and varieties of lichenised and lichenicolous fungi. The genus thrives in temperate to arctic-alpine regions of the Northern Hemisphere. Arthrorhaphis alpina, A. citrinella and A. grisea extend their distributions into the Southern Hemisphere [1], and A. citrinella var. catolechioides is restricted to Australasia [1]. Arthrorhaphis is well-studied in Europe and Central Asia [2,3,4], but species delimitation of taxa containing pulvinic acid derivates remains problematic. Arthrorhaphis alpina and A. citrinella in particular show considerable morphological variation at the world level that is presently not well understood. Material and Methods: New mitochondrial (mtSSU) and nuclear (nLSU, RPB1 and ITS 2) DNA sequences were generated for 142 specimens representing all currently described Arthrorhaphis species except A. aeruginosa*. We sequenced specimens from all continents. Due to the availability of collections, our sampling is biased towards northern and central Europe and parts of central and eastern Asia. All specimens were identified following current species concepts and the key morphological characters were noted. We applied Bayesian methods of phylogenetic tree reconstruction to the concatenated alignment of all four gene loci. Principal results: All lichenised species of Arthrorhaphis containing pulvinic acid derivates are monophyletic and apparently closely related Except for A. jungens, all species are recovered in our phylogeny according to the current morphology based concepts Ascospore type and presence / absence of Ca-oxalate crystals are confirmed as good characters for separating A. alpina s.l. (incl. A. vacillans and A. jungens) and A. citrinella s.l. A. alpina s.l. and A. citrinella s.l. comprise several genetically distinct lineages being correlated with morphology and / or geographical distribution The obligate parasitic taxa are separated by long branches and placed together in a basal position on the phylogenetic tree