First endocarp record of Miquelia (Icacinaceae) from the late Miocene of northern Vietnam and its phytogeographical and paleoecological implications

Abundant fossil records of Icacinaceae have been documented in the Northern Hemisphere; however, they are rare in the paleotropics where the family is most diverse today. As such, the evolutionary history of the family remains incomplete. In this study, we describe a newly discovered endocarp of Icacinaceae from the late Miocene of northern Vietnam, namely Miquelia yenbaiensis N.B. Hung, J. Huang & S.F. Li sp. nov. The identification is based on detailed morphological observations conducted using a reflected light microscope, together with extensive comparisons with both modern and fossil endocarps of the Phytocreneae. Miquelia yenbaiensis is characterized by sharp, thin, and reticulate ridges, with five main longitudinal ridges, and primarily circular pits arranged in longitudinal lines, with approximately 110-120 pits per face. The fossil examined in our study represents the first fossil record of Miquelia, indicating that this genus existed in northern Vietnam since at least the late Miocene. Additionally, our fossil finding provides the most recent fossil record of the Phytocreneae as well as the Icacinaceae, extending their historical range into tropical Asia during the late Miocene. Miquelia yenbaiensis likely inhabited a wet tropical ecosystem with a multi-stratified forest in the Yen Bai Basin during the late Miocene.