Epiphylly in angiosperms

Epiphylly is the occurrence of structures (leaves, shoots, inflorescences, etc.) on leaves. Although its occurrence was recognized without comment early in the history of descriptive botany, with the development of the classical shoot theory it became necessary to explain the deviation of leaves bearing epiphyllous structures (ES) from the positional criteria of this theory. Epiphyllous inflorescences have been interpreted primarily as resulting from the intervention of fusion, in order to retrieve the structures and positional relationships required by the classical theory. Epiphyllous buds, branches, leaves, etc. were regarded principally as accidental deviations from the accustomed positional relationships. There seems, however, to be some validity to the minority opinion of some earlier workers who rejected rigid application of the positional criteria of the classical shoot theory (and its consequent ad hoc explanations) to situations like epiphylly. Naturally occurring ES in the flowering plants are reviewed, as well as some of the results and implications of studies of the ontogeny of these structures. Finally, the significance of epiphylly is discussed with respect to our understanding of the shoot of Angiosperms, and the occurrence of intermediate structures. It seems best to dispense with the position criteria of the classical shoot model, and to accept leaves bearing ES as such, without further interpretation. This can be done in the context of newer models of the shoot which lack rigid criteria of position and which accept intermediate structures (such as leaves bearing ES) as such. In addition, ES raise important questions about the relationships between adaptation, morphogenesis, and phylogeny. In particular, a great deal remains to be learned about the adaptive significance of ES, particularly inflorescences. /// L'épiphyllie est l'occurrence de structures (structures épiphylles, abbr. SE: feuillées, tiges, inflorescences etc.) sur les feuilles. Ce phénomène fut remarqué assez tôt dans l'histoire de la botanique descriptive, mais c'est le développement de la théorie classique de la pousse qui exigea une explication des SE, qui ne s'y conforment pas. Pour sauver la théorie classique des structures et des relations structurales, les inflorescences épiphylles furent considérées comme des fusions congénitales entre inflorescence et feuille, et les pousses, feuilles, etc. épiphylles furent regardées comme des productions adventives. Et pourtant, i