Adjusting Subspecific Boundaries of the Wild Banana Musa acuminata Complex (Musaceae) in Thailand based on Morphological and Genetic Variations

Thailand, a recognized cradle of wild banana Musa acuminata diversity, has long been considered home to four subspecies: siamea , burmannica , malaccensis and microcarpa . However, recent extensive field surveys across the country have unveiled a more complex picture, necessitating a revision of their taxonomic classification. This study revisits the subspecific classification of M. acuminata in Thailand, reassessing the boundaries, descriptions, and distributions of previously reported subspecies using morphological and molecular data. Our findings reveal a distinct new subspecies, M. acuminata subsp. kraburiensis , located in the Kra Isthmus. This subspecies occupies a transitional zone between M. acuminata subsp. siamea in northern Thailand and M. acuminata subsp. malaccensis in peninsular Thailand. Notably, we also discovered a northern occurrence of the latter subspecies, suggesting a potential dispersal route along the Thailand-Myanmar mountain range. Furthermore, we document novel forms within existing subspecies, i.e., yellow bract mutants and aberration of male inflorescence architecture, in addition to a new subspecific record of subsp. truncata in Thailand. Conversely, neither subsp. burmannica , subsp. burmannicoides nor subsp. microcarpa were observed during this study. Based on our comprehensive analysis of the M. acuminata complex in Thailand, we advocate for maintaining subspecific rather than varietal designations. A key for identifying M. acuminata subspecies in Thailand based on critical diagnostic characters including leaf base shape, rachis position, and the aestivation and colour of male bracts, is presented.