Angiosperm floral evolution: Morphological developmental framework

This chapter brings together aspects of floral development and evolution in angiosperms derived from the diversity of structures of extant plants. It provides a framework especially, addressed to evolutionary developmental biologists. It attempts to show the spectrum of forms with special emphasis on extremes. Part of the processes discussed here have been addressed by molecular developmental geneticists, others have not yet been tackled. Topics are the contingency of the primary morphological surface of the flower, the sequence of the origin of floral organs in evolutionary history (organ categories, "organ identities"), patterns of floral phyllotaxis and symmetry, patterns of angiospermy, the significance of postgenital and congenital fusion for synorganization, the difference between autonomous and imprinted components of organ form, architectural extremes and limits discussed with the example of increased carpel number in whorled gynoecia, the decoupling of the sequence of stamen initiation from the normal centripetal floral organ initiation by ring meristems, and some potential pitfalls of generalizations extrapolated from model plants.