Unexpected diversity of flower-associated Aureobasidium reveals sixteen novel species from northern Thailand.

Aureobasidium species are widely distributed fungi commonly associated with diverse ecological niches, including floral environments. However, their diversity in tropical regions, particularly in flower-associated habitats, remains poorly explored. During a survey of fungi associated with flowers from diverse plant hosts in northern Thailand in 2024, a total of 54 Aureobasidium strains were isolated from 31 flower species. Based on a polyphasic approach integrating multilocus phylogenetic analyses, morphological and physiological characteristics, and growth temperature profiles, these strains were identified as 16 novel species (Aureobasidium anthicola sp. nov., A. bougainvilleae sp. nov., A. catharanthi sp. nov., A. chiangmaiense sp. nov., A. florale sp. nov., A. floricola sp. nov., A. florigenum sp. nov., A. kwanphayaoense sp. nov., A. lannaense sp. nov., A. oroxyli sp. nov., A. phayaoense sp. nov., A. plumeriae sp. nov., A. pollinicola sp. nov., A. saisamorniae sp. nov., A. savitreeae sp. nov., and A. siamense sp. nov.) and five previously known species (A. albui, A. castaneae, A. melanogenum, A. musti, and A. tremulum). Species within the A. melanogenum and A. thailandense groups were delimited as novel species based on the genealogical concordance phylogenetic species recognition (GCPSR) concept, supported by pairwise homoplasy index tests and physiological traits. Carbon assimilation profiles represent useful phenotypic characteristics for distinguishing closely related species. Moreover, these are the first geographic records of A. albui, A. castaneae, A. musti, and A. tremulum in Thailand. Full descriptions, color photographs, illustrations, and a phylogenetic tree showing the phylogenetic positions of the Aureobasidium species obtained in this study are provided. This study highlights floral habitats as important and previously underexplored ecological niches for Aureobasidium in tropical ecosystems, providing new insights into its diversity, ecology, and distribution.