A combination of embryological characteristics clearly defines Myrtales as comprising Combretaceae, Lythraceae (including Punicaceae and Sonneratiaceae), Melastomataceae, Myrtaceae, Onagraceae, Oliniaceae, Penaeaceae, and Trapaceae, a circumscription that agrees with that of the "core" Myrtales given by Dahlgren and Thorne (1983). The ordinal characteristics are: 1) anther tapetum glandular, 2) ovule crassinucellate, 3) inner integument 2-layered (except in Syzygium), 4) micropyle formed by both integuments (except in Syzygium and Trapa), 5) antipodal cells ephemeral or absent, 6) endosperm formation Nuclear type and 7) seed exalbuminous. Haloragaceae, Lecythidaceae, and Thymelaeaceae definitely should be excluded from Myrtales on the basis of differences in three or more of these primary defining characteristics. On the other hand, embryological evidence does not contradict the possibility of a relatively close relationship between Elatinaceae and Myrtales, even though an overall consideration of their features seems to make such a relationship seem less likely. Embryological evidence indicates a considerable degree of heterogeneity in Rhizophoraceae, a family or group of families that is clearly not assignable to Myrtales.