Fig. 8

The realization that a reproductive program can be activated in the intercalary meristem of individual equisetacean internodes, leading to development of sporangiophores along them, opened up a new avenue for interpreting the reproductive structures of extinct (Cruciaetheca, Peltotheca) and living (Equisetum) equisetaceans as illustrating a cumulative sequence of deployment (gray arrow at top) of independent regulatory modules for three developmental processes (in purple, at bottom) responsible for the different features (in black, at bottom) that characterize specific reproductive morphologies; cross bars separate phytomers in the shoot diagrams and phytomers bearing sporangiophores are red; modified from [47]