Abstract: The genus Phaeolus holds significant economic and ecological value as an important pathogen of conifer trees. Although species diversity within this genus has been described in recent years, there were limited studies of its origin, evolution, and biogeography. In this study, we collected new specimens from China and USA, and reconstructed the phylogeny, divergence times, and biogeography of Phaeolus based on ITS and nLSU sequences. Phylogenetic analyses identified two new species, Phaeolus himalayanus and Phaeolus occidentiamericanus, one new combination, Phaeolus hispidoides, one synonym, Phaeolus fragilis (treated as P. schweinitzii), and one new record from China, Phaeolus sharmae. Phaeolus himalayanus is characterized by pileate, imbricate basidiomata, round to irregular pores of 2-3 per mm, abundant gloeoplerous hyphae, mango-shaped to ellipsoid basidiospores (5.5-7 × 4-4.5 µm), and distribution in Xizang of China. Phaeolus occidentiamericanus is characterized by pileate, imbricate basidiomata, round to irregular pores 2-3 of per mm, mango-shaped to ellipsoid basidiospores (6.5-7.8 × 4-5 µm), and distribution in the western USA. Molecular clock analyses indicated that the genus Phaeolus likely originated in the Late Cretaceous, with species divergence occurring between 9-71 Mya. Ancestral state reconstruction suggested that the genus originated in the Himalaya-Hengduan Mountains region and subsequently dispersed to Europe and North America. The earliest host trees of Phaeolus were probably Abies and Pinus, with all known species capable of growing on Pinus, demonstrating a strong host trees preference. Additionally, a key of the genus Phaeolus is added. This study provides a crucial foundation in pathogen control and ecological conservation of this genus in the future.

Key words: Wood-inhabiting fungi, Phaeolaceae, Taxonomy, Fungal pathogens, Himalayan