Articulation Morphology of Plants and Plant Evo-Devo: An Open Morphology—Empirical, Dynamic, All-Inclusive, and Unifying

In Articulation Morphology, inspired by the theory of anaphytes that was first proposed in 1843, ramification is the key principle in plant morphology in the open growth of plants. It engenders articulation: the formation of articles, called anaphytes. While the theory of anaphytes included tenets that are now considered outdated, Articulation Morphology—proposed here as a modern version of this theory—retains and further develops only those aspects that remain valid and fundamentally important, namely ramification and articulation. In this view, plants are articulated wholes: systems of articles formed through ramification and articulation: the formation of articles. These articles are understood dynamically as process combinations according to process morphology. For practical purposes, they may be described in traditional structural terms such as root, stem, leaf, or leaflet, but without implying a controversial and limited morphological theory such as the classical root–stem–leaf theory of mainstream morphology. Hence, articulation morphology is strictly empirical, solely relying on the observable processes of open growth, ramification and articulation. In contrast to classical mainstream morphology, which often fails to accommodate atypical or deviant structures, articulation morphology is all-inclusive: even the most deviant structures can be understood as deviant patterns of ramification and articulation. Furthermore, articulation morphology is unifying because articles constitute a fundamental morphological unit that applies to all plants from algae to bryophytes and vascular plants, whereas organ-centred classical mainstream morphology lacks such a fundamental unifying unit for all plants. Within this framework, the central concept of articulation morphology is no longer homology but transformation—the transformation of ramification and articulation. Owing to this fundamental shift and to its empirical, dynamic, all-inclusive, and unifying foundation, articulation morphology may be regarded as a new paradigm for plant morphology—an open morphology. From this perspective, plant evo-devo, especially plant morpho evo-devo, becomes the investigation of the development and evolution of ramification and articulation.