Taxonomic reconsideration of a sequestrate fungus, Octaviania columellifera, with the proposal of a new genus, Heliogaster, and its phylogenetic relationships in the Boletales

Abstract

During taxonomic revision of genus Octaviania in Japan we examined herbarium and fresh specimens of O. columellifera and O. asterosperma sensu S. Yoshimi & Y. Doi with morphological and molecular techniques. These two species were identical in both macro- and micromorphological characters and were clearly different from the generally known O. asterosperma. The identity of the two species and their distinctness from O. asterosperma was further supported by both nuclear large subunit and ITS rDNA phylogeny. The molecular analyses also revealed that O. columellifera shares its lineage with the boletoid mushroom-forming Xerocomus chrysenteron complex and that it does not form a monophyletic clade with other Octaviania species. Our morphological reevaluation, including transmission electron microscopic observation of basidiospores, clarified the taxonomic boundary between O. columellifera and other Japanese Octaviania species. Accordingly we propose a new genus, Heliogaster, for O. columellifera with designation of the lectotype. We discuss phylogenetic relationships with Octaviania sensu stricto species and the closely related boletoid (pileate-stipitate) fungi, generic characters of Heliogaster and intraspecific phylogeny.

• Boletaceae
• hypogeous fungi
• Octavianina
• systematics
• taxonomy
• truffle-like fungi

We appreciate the significant contribution of amateur Japanese mycologist Mr Sho-ichi Yoshimi (1928–2003). We are grateful for the help of Dr Tsuyoshi Hosoya, Dr Kentaro Hosaka (TNS), Mr Daisuke Sakuma (OSA) and Dr Yousuke Degawa (KPM) who allowed access to herbarium specimens and depositing of our specimens. We gratefully acknowledge Dr Ken Katumoto for checking the Latin diagnosis and for valuable comments on this manuscript. We also thank Mr Taiga Kasuya, Mr Toshiaki Inose, Mrs Atsuko Hadano, Mr Sumio Honda, Mrs Michiyo Nabe, Mr Mitsuo Nabe, Mr Eiji Nagasawa, Mr Minoru Nakajima, Mr Masaru Ohkubo and Mr. Etsuzo Sano for providing specimens. Mr Toshiyuki Tokiwa kindly gave valuable comments on identification of anamorphic ascomycetes Sepedonium chrisospermum and S. chlorinum. We also are grateful for the help of Mr. Yu-zou Kotera who provided valuable literature on Japanese sequestrate fungi.