The history of the endemic flora of St Helena: late Miocene:‘Trochetiopsis-like’ pollen from St Helena and the origin of Trochetiopsis



Re-examination of a fossiliferous sediment from St Helena has revealed the presence in the late Miocene of pollen grains very similar to modern Trochetiopsis pollen. Trochetiopsis is found only in St Helena and is assumed to be a palaeoendemic genus. The late Miocene material provides striking confirmation of this view.

The two extant Trochetiopsis species are compared with other species in the Sterculiaceae: Dombeyeae, using multivariate methods. It is suggested that the two extant Trochetiopsis species diverged on St Helena comparatively recently, probably as a result of disruptive selection followed by ecological isolation caused by environmental change at the beginning of the Quaternary.

It is also suggested that the ancestor of the extant Trochetiopsis species arrived in St Helena by long distance dispersal from African or Madagascar Dombeyeae stock at least 9 million years ago. However, since this time the pollen morphology of the Trochetiopsis lineage has changed little. The taxonomic isolation of Trochetiopsis can thus be explained partly by evolution on St Helena, but mainly by evolution and extinction in the Dombeyeae elsewhere (reliction).