XVI International Botanical Congess

A haplobiontic ancestry for vascular plants implies that complex sporophytes evolved from a new growth cycle interpolated between zygote formation and meiosis (Bower, 1908). A significant delay of meiosis could produce a sporophyte big enough to reproduce while a portion of the protoplasm remained non-sporogenous. This new tissue surplus created opportunities for ancillary gender-based features (now seen most clearly in angiosperm sporophytes) to evolve. Gender-based traits in seed plants may have no strict morphological counterparts in the gametophyte generation. However, identical genes controlling gender-specific traits in ancient haploids may have been recruited for diploid expression as sporophyte gender evolved. Homosporous pteridophytes allow genes expressed in a gender-specific fashion in haploids to be identified, and potentially traced to heterosporous lineages where sporophytes express gender.