Delimitation of the wild banana Musa acuminata subspecific complex (Musaceae) in Thailand

Thailand, a recognized cradle of diversity for the wild banana Musa acuminata, 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 circumscriptions, descriptions, and distributions of previously recognized subspecies using morphological and biogeographic evidence. The findings reveal a distinct new subspecies, M. acuminata subsp. kraburiensis, located on the Isthmus of Kra. This subspecies is distributed in the transitional zone between M. acuminata subsp. siamea in northern Thailand and M. acuminata subsp. malaccensis in Peninsular Thailand. Furthermore, a northern occurrence of the latter subspecies was recorded, suggesting a potential dispersal route along the Thailand-Myanmar mountain range. Fieldwork revealed additional novel forms within existing subspecies, i.e., a putative mutant form with yellow inflorescence bracts and another form with unusual branching of the inflorescence. Finally, M. acuminata subsp. truncata was recorded for the first time in Thailand. Musa acuminata subsp. burmannica, M. acuminata subsp. burmannicoides, and M. acuminata subsp. microcarpa were not observed during the field survey. Based on the analysis of the M. acuminata subspecies complex in Thailand, the variation is best treated at the subspecies rather than the varietal level. A key for identifying M. acuminata subspecies in Thailand is presented here based on diagnostic characters such as leaf base shape, rachis position, imbrication type, and color of the male bracts.