Comparative Ovule and Megagametophyte Development in Hydatellaceae and Water Lilies Reveal a Mosaic of Features Among the Earliest Angiosperms

Most features of the ovule and embryo sac of Trithuria are consistent with a close relationship with other Nymphaeales, especially Cabombaceae. The frequent occurrence of double megagametophytes in the same ovule indicates a high degree of developmental flexibility, and could provide a clue to the evolutionary origin of the Polygonum-type of angiosperm embryo sac.