Major shifts in embryo size occurred early in the evolutionary history of angiosperms

Seeds are the main dispersal and propagation units of angiosperms. Examining the relative allocation of seed reserves by quantifying the relative embryo size (ES) at dispersal (i.e. size of the embryo relative to the seed) across angiosperms, sets the basis to track the evolutionary history of this key reproductive trait related to germination timing and offspring survival. We used a robust, dated phylogeny and sampling of ES for selected species across most angiosperm families to model the macroevolution of ES. Data on ES were collated from living specimens and primary literature. Early angiosperms typically had a low ES, which is still reflected in contemporary magnoliids and ANA-grade species. The analysis of major evolutionary shifts in ES throughout angiosperm phylogeny revealed that these shifts were predominantly associated with the formation of the main angiosperm lineages. The tempo and mode of ES evolution were not constant over angiosperm history, paralleling major paleo-events. This study provides crucial new insights in seed trait evolution, which contribute to understanding the diversification of reproductive strategies in angiosperms.