Seed dormancy acquisition and alleviation was studied in four Caesalpinioid legumes from eastern North America including honeylocust (Gleditsia triacanthos L.), water locust (Gleditsia aquatica H. Marshall), Kentucky coffeetree (Gymnocladus dioicus (L.) Koch.), and redbud (Cercis canadensis L.). Special attention was paid to the role of the micropyle in water loss during seed development and water uptake following dormancy release. Anatomical observations suggest that the micropyle in all species except eastern redbud remains open late in seed development to aid in seed desiccation coincident with acquisition of physical dormancy. The micropyle in eastern redbud is intimately associated with the hilum forming a hilar slit that appears to perform a similar function. Following dormancy release, the primary water gap in honeylocust and water locust is the lens, but the micropyle also functions as a water gap during initial imbibition. For eastern redbud, the initial water gap is the hilar slit. Blocking water penetration using petroleum jelly over the hilar slit completely eliminates water uptake following dormancy release. It can be concluded that the micropyle along with the lens in locust and the hilum in eastern redbud plays a role in dormancy release in physically dormant Caesalpiniod legumes.