Fossil Hyaenanche Pollen from the Eocene of Kenya: The Paleophytogeograpy and Paleoclimate of a Relict Plant Genus Endemic to the Cape Province, South Africa

On the African continent, Picrodendraceae are represented by four genera. Their intracontinental paleophytogeographic histories and paleoecological aspects are obscured by the lack of pre-Miocene fossils. For this study, late Eocene sediments from Kenya were investigated. The sample was prepared in the laboratory, and its organic residue was screened for pollen. We extracted fossil Picrodendraceae pollen and investigated the grains using light and scanning electron microscopy. Based on the pollen morphology, the grains were assigned to Hyaenanche. This genus is currently confined to a small area within the Cape Province, South Africa. There, the plants grow as shrubs and small trees at an elevation between 60 and 800 m, on rocky substrate, as part of open fynbos vegetation, and under a dry climate with hot summers and limited precipitation. The sedimentary context and the associated palynoflora suggest that during the Eocene of Kenya, Hyaenanche was part of lowland coastal vegetation in Eastern Africa. There, the plants grew under fully humid to winter-dry tropical climates as part of landwards margins of mangroves, seasonally inundated floodplain forests, or coastal forests. Our study shows that when evaluating paleoecological aspects of relict monotypic plants, their extant closely related genera and their fossil records need to be considered.