XVI International Botanical Congess

During the Carboniferous, several tracheophyte clades independently evolved laminated, multiveined leaves broadly similar to those of extant ferns. Leaf development in living plants provides a framework for interpreting the early leaf record. Analysis of leaf floras drawn principally from Great Britain suggests all Carboniferous leaves were produced by marginal meristems. Each plant group independently followed similar steps in the evolution of marginal growth from ancestors capable only of apical growth, but their methods of development diverged with later innovations. Each developmental mechanism can produce only a limited set of forms and morphospace occupation through time can be linked to specific developmental innovations. Hypotheses of meristematic evolution can be tested by comparison of teratologies found in fossil and living plants of known development.