European Palaeobotany and Palynology Conference 2026

Information on the order in which pleisiomorphic angiosperm characters arose may be helpful in identifying the most likely close stem-relatives or ancestors of angiosperms from the fossil record. We have developed a method to determine the sequence of acquisition of angiosperm-specific traits by exploiting gene and genome duplication events as temporal reference points. As a test case, we have analysed the evolution of the YABBY transcription factor family. Our data suggest a model in which two ancestral YABBY genes were present in the most recent common ancestor of living seed plants, one of which was expressed specifically in reproductive tissues. This gene appears to have been lost from a common ancestor of living gymnosperms, but underwent successive duplications along the angiosperm stem lineage to generate three gene lineages that promote the development of distinct sets of reproductive organs. From these data, we postulate that the hypothesized reproductively expressed YABBY gene promoted the expansion of an ovulate cupule in early seed plants, and that this structure became the outer integument of the ovule in angiosperms. This hypothesis is consistent with the proposition of cupulate gymnosperms such as Caytoniales as close stem-relatives or ancestors of angiosperms.