Phylogenetic patterns of morphological and chemical characters and reproductive mode in the Heterodermia obscurata group in Costa Rica (Ascomycota, Physciaceae)

Species delimitation in lichens of the Heterodermia obscurata group (sect. Polyblastidium) is based on reproductive mode, lobe underside pigmentation, and medullary chemistry as main character complexes. However, these characters are inconsistently used by different workers, and phenotypes with different medullary chemistry or underside pigmentation are often lumped into single species. In addition, molecular studies in other genera of Physciaceae have shown that phenotypes reproducing either sexually or asexually do not necessarily form monophyletic clades, which does not support the species pair concept postulating that vegetatively reproducing species form monophyletic sister clades to sexually reproducing species. Obviously, these deviating concepts greatly influence the number of species recognised in biotic inventories, as is the case in the Costa Rican Lichen Biodiversity Inventory (Ticolichen). Here, depending on which species concepts are used, the number of taxa recognised in the H. obscurata group varies between 10 and 25. We therefore tested the phylogenetic patterns of distribution of morphological and chemical characters and reproductive mode in apotheciate versus sorediate taxa of the H. obscurata group in Costa Rica by means of molecular phylogenetic analysis of ITS sequences. Based on our results, the use of both medullary chemistry and underside pigmentation for the distinction of species is supported, which is in contrast to the concepts used in recent treatments of the genus. The data are ambiguous, however, with regard to the species pair concept: in the case of H. flabellata vs. H. obscurata, the species pair concept does not seem to hold, while in two other supposed species pairs (Heterodermia ’rottbollii’ vs. H. ’pseudobscurata’ and H. ’violacea’ vs. H. ’reagens'), the sorediate forms appear not to be sister taxa of the apotheciate forms.