Revision of the Genus Cyanoboletus (Boletaceae) in the Mediterranean Basin with Notes on Arsenic Hyperaccumulation

This study revises the genus Cyanoboletus (Boletaceae) in the Mediterranean Basin, integrating single-locus and multi-locus phylogenetic analyses (ITS, LSU, tef1-α, and rpb2), morphological characterisation, ecology, and arsenic accumulation in basidiomes. Morphological descriptions (including a new form, Cyanoboletus mediterraneensis f. pallidus), comprehensive sampling, type studies, biogeography, macro- and microphotographs, an identification key, and a historical overview of the nomenclatural issues surrounding C. pulverulentus, C. poikilochromus, and C. mediterraneensis are given. An epitype collection is designated for C. pulverulentus. A new method to measure spore suprahilar depression has been proposed, which allowed more clear morphological separation between C. mediterraneensis and C. pulverulentus. This method may prove useful for species delimitation in other fungal groups that have asymmetric basidiospores. Additionally, we generated a new ITS sequence of the C. sinopulverulentus holotype and inferred its conspecificity with the later described C. flavocontextus. Furthermore, notes on the taxonomy of Boletus gabretae are presented, and its placement in the genus Neoboletus is suggested. Cyanoboletus is confirmed as a strongly supported generic clade encompassing 21 monophyletic species-level clades, 14 of which represent known species, and seven are undescribed taxa. The synonymy of Cupreoboletus with Cyanoboletus is also verified. This publication provides the tools to delimit Cyanoboletus species that have important conservation value, which can be used by conservationists, ecologists, and citizen scientists. It also highlights species-specific arsenic hyperaccumulation in C. pulverulentus, contributing to a better understanding of fungal metal uptake. Our study indicates that within Cyanoboletus, only C. pulverulentus demonstrates this characteristic and is the only known member of Boletales that possesses a high arsenic accumulation ability.