Young open carpels with developing ovules exposed to view are a regularly observed stage in development in 25 caesalpinioid species and one papilionoid legume studied. In all, the carpel margins later become appressed and sealed. A literature survey revealed examples of open, ovulate carpel primordia in 42 species in 19 additional angiosperm families. The feature of angiospermy, or enclosed ovules, is achieved gradually during ontogeny in the taxa studied, rather than being present ab initio. This heterochronic lag of carpel closure may be viewed as either precocious timing of ovule initiation or as delayed timing of carpel closure, compared to other legumes with closed carpels at ovule initiation.