Megasporogenesis and megagametogenesis in species of Annonaceae, the largest family of early-diverging angiosperms

There are few data on female embryology of Annonaceae (Magnoliales), and nothing for the genera Duguetia and Guatteria. We describe megasporogenesis and megagametogenesis of seven species of Annonaceae, indicating similarities and differences that are useful for taxonomic and phylogenetic analyses of the family. Ovules were analysed using light microscopy. The ovules are bitegmic, perichalazal and anatropous, except in Duguetia furfuracea (anacampylotropous ovules). In the young crassinucellate ovule, an archesporial cell differentiates to become a megasporocyte and a linear tetrad of megaspores is produced after meiosis. The three micropylar megaspores degenerate and the chalazal one produces the megagametophyte. Three mitoses produce eight nuclei and seven cells: three antipodals, two synergids, an egg cell, and a binucleate central cell, resulting from the migration of two nuclei to the central region. This development is characteristic of the Polygonum type. The species studied exhibit considerable uniformity in female embryological development, corroborating data found in the literature.