Anaxagorea is the phylogenetically basal-most genus in the large, tropical magnoliid family Annonaceae (custard apple). Endress and Armstrong study floral development for the first time in the genus and show complex whorled floral phyllotaxis, with double organ positions in the outer androecium whorl resulting in a switch from trimery to hexamery and completely plicate carpels. The floral phyllotaxis shows that there is no signature of a basal spiral pattern in Annonaceae and that complex whorls are an apomorphy not just for a part of the family but for the family in its entirety, and irregular phyllotaxis is derived.
