Developmental evolution of endosperm in basal angiosperms: evidence from Amborella (Amborellaceae), Nuphar (Nymphaeaceae), and Illicium (Illiciaceae)

Because of their basal phylogenetic position, Amborella, Nymphaeales, and I lliciales (and allies) are key to reconstructing ancestral character states and to tracing character state transitions that occurred during the earlie st radiation of flowering plants. Endosperm is the sexually-derived embryo- nourishing tissue that is unique to the life cycle of angiosperms, We provi de detailed descriptions of endosperm development in Amborella. Nuphar (Nym phaeates), and Illicium (Illiciales) and compare patterns within an explici t phylogenetic context for the three basal lineages that they represent. Am borella and Illicium share a bipolar, cellular pattern of development. char acterized by an oblique first division, that was resolved as ancestral for flowering plants. A series of character state transformations occurred with in Nymphaeales which led first to a modified cellular pattern with a transv erse first division (present in Nuphar). The transverse cellular pattern wa s transformed to a helobial pattern that is present in Cabombaceae. Endospe rm ontogeny involves dissociable elements and appears to fit the model of a modular developmental process.