Classical Morphology and Continuum Morphology: Opposition and Continuum

Classical plant morphology still provides the conceptual framework for most phytomorphological investigations and highly relevant concepts and data for other botanical disciplines such as plant morphogenesis, molecular genetics, ecology, systematics, evolutionary plant biology, etc. Typical classical morphology is categorical, i.e. the diversity of plant form is reduced to mutually exclusive morphological categories such as root, shoot, stem (caulome), leaf (phyllome), and trichome. In contrast, continuum morphology established a morphological continuum between all these categories. As a consequence, homology becomes a matter of degree. Hence, the difference between continuum morphology and classical morphology is striking. Nonetheless, the two approaches and views need not be seen as opposed to each other. They can be considered complementary: classical morphology emphasizing the difference between typical representatives of morphological categories and continuum morphology stressing the continuum between these fuzzy categories. Furthermore, if the morphological categories are interpreted as extreme types, which by definition are fuzzy and continuous with each other, then classical morphology becomes continuum morphology. If such reinterpretation occurs only to some extent, intermediate positions between typical classical morphology and continuum morphology result. Examples of various intermediate positions indicate that a continuum exists between typical classical morphology and continuum morphology. Hence, there is not only a continuum between morphological categories but also between approaches to and views of the field of plant morphology. Consequences of this reconciliation are briefly discussed.