Two new species of Fulvifomes (Basidiomycota, Hymenochaetaceae) on threatened or near threatened tree species in Japan.

We describe two new species of Fulvifomes based on morphological observations and phylogenetic investigations. Both species were identified as Phellinus rimosus by former mycologists, but both are morphologically distinct from authenticated specimen of P. rimosus. Fulvifomes boninensis is characterized by perennial basidiomata, a sulcate pileus surface becoming rimose, lack of a distinct crust on the pileus surface, subdimitic hyphal system in the context, and ellipsoid basidiospores. This species is endemic to the Bonin Islands, Japan, and is specific to the host Morus boninensis, a red-listed tree species. Fulvifomes imazekii is characterized by perennial basidiomata, sulcate and velutinous pileus surface, lack of a crust on the pileus surface, dimitic hyphal system in the context, and broadly ellipsoid basidiospores. This species is specific to Berchemiella berchemiaefolia, and is known only from Mt. Yokogura-yama, in Kochi Prefecture, Japan. Fulvifomes boninensis and F. imazekii are considered threatened, because of their high host specificity each with a threatened tree species as well as the limited distribution of the former and the extremely small number of "mature individuals" of the latter. The following new combinations were also proposed: Fulvifomes aulaxinus, F. pappianus, and F. tepperi.