Kaplan’s Principles of Plant Morphology: A Critical Review

Abstract

"We should not confuse our favourite metaphors (including concepts such as root, shoot, leaf and flower) with reality, which is more complex" (Kirchoff et al., 2008). Kaplan's Principles of Plant Morphology (2022) by Donald R. Kaplan, edited by Chelsea D. Specht, is a monumental work of 1305 pages in a large format. It presents a wealth of well-organized morphological data that are relevant not only to plant morphology but also to many other fields such as plant genetics, molecular biology, evolution, systematics, biodiversity, crop science, etc. The interpretations of the data are in terms of classical plant morphology, a rigid typological framework that Kaplan adopted from Troll (1937-1943). Before I discuss this typologi-cal framework of classical plant morphology, a few comments on the fundamental importance and relevance of plant morphology in general. Plant Morphology Remains Important For centuries, plant morphology, besides plant physiology, genetics, ecology, and systematics, has been one of the basic disciplines of plant biology or botany. Hence, universities offered courses in plant morphology. But nowadays this is no longer the case. Plant morphology has been absorbed into Evolutionary Developmental Biology (Evo-Devo). This does, however, not diminish the importance and relevance of plant morphology. Besides molecular genetics, morphology remains an integral part of evo-devo. To emphasize the importance of morphology, Wanninger (2015) referred to MorphoEvoDevo. Minelli's comprehensive book on plant evo-devo has as its subtitle "The evolvability of the phenotype" (Minelli, 2018). Kaplan emphasized that plant morphology is more fundamental than plant anatomy, which deals with tissues, cells, and subcellular components. He devoted a whole chapter of his book to this topic where he pointed out that "organ differentiation is independent of the arrangement of cell and tissue types and even multicellularity itself. For example, the various siphonous greens, such as Bryopsis and Caulerpa,