Phylogenetic relationships and taxonomy of the Leptogium lichenoides group (Collemataceae, Ascomycota) in Europe

Leptogium (Ach.) Gray is a cosmopolitan genus of lichen-forming ascomycetes classified in the Collemataceae and represented by c. 250 species with about 40 infrageneric taxa found in Europe (Aragón & al., 2005). Several complexes have been studied within this morphologically and anatomically heterogeneous genus by different authors (Jørgensen, 1975, 1994, 1997; Jørgensen & James, 1983; Jørgensen & Tønsberg, 1999). However, different taxonomic questions relating to many species complexes and groups remain to be resolved. One of these is the lichenoides species complex, which includes four species in Europe: L. intermedium (Arnold) Arnold, L. gelatinosum (With.) J.R. Laundon, L. lichenoides (L.) Zahlbr. and L. quercicola Otálora & al. (Otálora & al., 2004). Although species of this group may display considerable morphological variability that hinders their identification, no taxonomic revision has been conducted for this species complex. Nomenclaturally, the main difficulty resides in the numerous infraspecific taxa recognized within L. lichenoides (Zahlbruckner, 1924; Lamb, 1963; Jørgensen, 1994). These taxa show considerable morphological differences and could represent distinct species. However, a morphological and molecular systematic study is required to distinguish between phenotypic plasticity and genetically based morphological differences. Leptogium lichenoides was originally described as Tremella lichenoides L. (1753). Many taxa have been introduced since then, some of which were correctly classified in the genus Leptogium when Gray (1821) recognized the genus Leptogium as a separate taxonomic entity from the genus Collema. Subsequently, Zahlbruckner (1924) included more taxa within the lichenoides species complex, and considered five different varieties (L. lichenoides var. lichenoides, var. lophaeum, var. pulvinatum, var. sendtneri, var. subsinuatum) as well as four different forms within var. lichenoides (f. ateleum, f. fimbriatum, f. laevigatum, f. luxurians). Morphologically, the lichenoides complex includes species with thin, paper-like, bluish-grey to brown thalli, and a distinctly ridged upper surface. Thalli cross sections reveal a well-developed lower and upper cortex made up of a single layer of cells (Otálora & al., 2004). Leptogium gelatinosum and L. intermedium are morphologically similar, although some differences in thallus anatomy and apothecial margin have been observed (Jørgensen, 1994; Aragón & Otálora, 2004). Both species are distinguishable from other taxa within the lichenoides complex, especially based on lobe margins, ridges on the lower surface of the thallus, and presence of apothecia, which are often numerous on thalli of L. gelatinosum (Coppins & Purvis, 1992; Jørgensen, 1994; Otálora & al., 2004). Phylogenetic relationships and taxonomy of the Leptogium lichenoides group (Collemataceae, Ascomycota) in Europe