Ramenta morphology and its variations in Rafflesia (Rafflesiaceae)

•Ramenta morphology is a taxonomic character that has not been used consistently.•Five basic types of ramenta with several variations within each type are proposed.•These types offer a tool for using consistent terminology to described Rafflesia.

Ramentae are hair-like structures found on the perigone tube and diaphragm in species of Rafflesia (Rafflesiaceae). Although ramenta morphology provides an important taxonomic character, a consistent terminology has not been used in species descriptions. As such, morphological comparisons among species as well as among populations within a species are difficult. We used a variety of resources to document the morphology including the location and density of ramenta among 18 species of Rafflesia and between populations and/or sexes of two species. We identified five types of ramenta: tuberculate, filiform, swollen apex, toadstool, and fence-like and recognized several variations within each type. Ramenta types characterize four species complexes: R. patma (tuberculate), R. arnoldii (filiform), R. pricei (mostly swollen apex), and R. hasseltii (mostly toadstool). Our classification of ramenta offers a tool for using consistent terminology to re-evaluate previously described species and to define new species of Rafflesia.