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RESEARCH PRODUCT

Plant Morphology: The Historic Concepts of Wilhelm Troll, Walter Zimmermann and Agnes Arber

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Recent molecular systematic and developmental genetic findings have drawn attention to plant morphology as a discipline dealing with the phenotypic appearance of plant forms. However, since different terms and conceptual frameworks have evolved over a period of more than 200 years, it is reasonable to survey the history of plant morphology; this is the first of two papers with this aim. The present paper deals with the historic concepts of Troll, Zimmermann and Arber, which are based on Goethe's morphology. Included are contrasting views of ‘unity and diversity’, ‘position and process’, and ‘morphology and phylogeny’, which, in part, are basic views of current plant morphology, phylogenetic systematics and developmental genetics. Wilhelm Troll established the ‘type concept’ and the ‘principle of variable proportions’. He has provided the most comprehensive overview of the positional relations of plant forms. Agnes Arber started from the universal dynamics of life and attempted to describe all structures as processes. She paid attention to ‘repetitive branching’, ‘differential growth’, and ‘parallelism’. As a result she has recently been rediscovered by developmental botanists. Walter Zimmermann rejected any metaphysical influence on plant form and instead called for objective procedures. He was mainly interested in phylogenetic ‘character transformation’ and the ‘reconstruction of genealogical lines’. Guided by the example of flower-like inflorescences, a future paper will deal with functional and developmental constraints influencing plant forms. Recent morphological concepts (‘trialectical’, ‘continuum’/‘fuzzy’, ‘process morphology’) will be discussed and related to current morphological and developmental genetic research.