Abstract
The sequestrate fungi of Japan, including truffle and truffle-like fungi, have not been well characterized but are potentially diverse. We investigated the diversity and phylogeny of Japanese Octaviania specimens using a multifaceted approach including scanning and transmission electron microscopy as well as analysis of nuclear ribosomal DNA (ITS and LSU) and EF-1α (tef1) sequences. Phylogenetic analyses indicate that the genus Octaviania is divided into three major clades, and that there are at least 12 species-level lineages in Japan. Accordingly, we describe two new subgenera, Parcaea and Fulvoglobus, and eleven new species. Subgenus Parcaea accommodates four highly divergent, but macromorphologically almost indiscernible cryptic species. We discuss not only the diversity and species delimitation within the genus Octaviania but also the phylogeography of the Japanese taxa and their relatives.