667Tobe, H. ' and Raven, PH.2 ('Department of Natural Environmental Sciences, Faculty of Integrated Human Studies, Kyoto University, Kyoto 606, Japan; 2Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166, U.S.A.) 1996. Embryology of Onagraceae (Myrtales): characteristics, variation and relationships . Telopea 6(4): 667-688. Here we report features of the embryology of 14 genera of Onagraceae, as a companion study to our earlier report on Ludwigia alone. We found that the 4-nucleate Oenothera type embryo sac that sharply distinguishes Onagraceae from all other Myrtales is common to all genera. Shared features of the nucellus and seed coat structure, however, indicate that Onagraceae more closely resemble Lythraceae than other Myrtalean families. Differences between onagraceous genera are found in 1) the mode of anther wall formation (the Basic or the Monocotyledonous type), 2) the number of cells in the ovule archesporium (one-celled or multi-celled), 3) the nature of early development of the inner integument (retarded or not retarded), and 4) the thickness of the parietal tissue in the nucellus (thin or thick). Based on comparisons in these and other embryological characteristics, we have concluded that: 1) Ludwigia (Jussiaeeae) differs sharply from the rest of the family in having a one-celled archesporium in its nucellus; 2) Hauya (Hauyeae) and eight of the genera of Onagreae (except Gayophytum) closely resemble one another but differ from the other genera of the family in their markedly thick parietal tissue in the nucellus; 3) Gayophytum, unlike other Onagreae, resembles Epilobium (now including Boisduvalia) in having retarded early development of its inner integument and in having thin parietal tissue; 4) Clarkia heterandra (formerly segregated as the monotypic genus Heterogaura) differs from other species of Clarkia and from other Onagreae (except Gayophytum) in its nucellar histology.