Pandanus sermolliana Callmander & Buerki (Pandanaceae) is described from humid forests in the Galoka mountain chain in northwestern Madagascar. The new species can be easily distinguished from the other members of the genus it most closely resembles, P. insuetus Huynh and P. perrieri Martelli, by several morphological characters, including drupes that are incompletely fused, with each of the dome-like carpels separated from the base of the pileus, and stigmas that are subvertical or rarely subhorizontal, slightly spinescent, and raised on an incompletely united base. This distinctive species is rare and is classified as Critically Endangered based on IUCN Red List criteria.