All in a spin: centrifugal organ formation and floral patterning.

Understanding floral patterning is a primary goal in plant biology, yet the temporal sequence of organ development is rarely factored into developmental models. In flowers, occasional examples of centrifugal or basipetal organ initiation, both within organ zones (intrazonal) and between them (interzonal), present a paradox with respect to developmental models. A centripetal/acropetal sequence of floral organ initiation is ancestral in angiosperms, but centrifugal/basipetal development has evolved many times, indicating that these apparently major developmental shifts have relatively simple genetic triggers. Review of the sequence of organ initiation in angiosperms supports evidence that the four floral organ types develop independently of each other, in response to genetic factors that predetermine radial patterning.