Inception of the cupule of Quercus macrocarpa and Fagus grandifolia

Abstract

The female inflorescence of Fagus grandifolia comprises two flowers; one flower terminates the first-order inflorescence axis, the other flower terminates the second-order inflorescence axis. Each flower is flanked by two cupular valves each of which arise in the axil of a bract. The two valves flanking the flower terminating the first-order inflorescence axis represent second-order inflorescence axes and the two valves flanking the flower terminating the second-order inflorescence axis represent third-order inflorescence axes. The four valves remain discrete. Each female flower of Quercus macrocarpa terminates a second-order inflorescence axis and is surrounded by a continuous cupule. The cupule first forms as two primordia in the axils of each of the two transversal second-order bracts. These cupular primordia represent third-order inflorescence branches. The cupule primordia become continuous about the pedicel by meristem extension. The cupules of Fagus and Quercus are homologous to the extent that they are modified axes of the inflorescence. This serves as a model to interpret the morphological nature of the fagaceous cupule.