Phylogenetic placement of Geastrum melanocephalum and polyphyly of Geastrum triplex

Geastrum melanocephalum, originally described as Trichaster melanocephalus, is characterized by large basidiomata and an evanescent endoperidium. Although Trichaster was recently treated as a synonym of Geastrum and the specific name G. melanocephalum has often been used, it is still controversial whether Trichaster is an independent genus. Although a close affinity of G. melanocephalum and G. triplex has been suggested based on some morphological similarities, it is highly likely that G. triplex is polyphyletic because of its high morphological variability. To clarify the phylogenetic position of G. melanocephalum, it is therefore critical to evaluate the monophyly of G. triplex. This study sampled ITS, LSU, and atp6 genes from 144 specimens of Geastrales including G. melanocephalum and G. triplex from several continents. Results of phylogenetic analyses demonstrated G. melanocephalum is nested within Geastrum and is most closely related to the European and North American group of G. triplex. Morphological similarities of G. melanocephalum and European and North American G. triplex are also suggested. Based on phylogenetic and morphological evidence, we confirm Trichaster is a synonym of Geastrum, and the scientific name Geastrum nocephalum should be accepted. Moreover, the present study revealed that taxa tentatively identified as “G. triplex” are highly polyphyletic, and a taxonomic revision of “G. triplex” is therefore needed.