Classical and dynamic morphology: toward a synthesis through the space of forms |
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Authors: | Bernard Jeune Denis Barabé Christian Lacroix |
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Institution: | (1) Institut de recherche en biologie végétale, Jardin botanique de Montréal, Université de Montréal, 4101 rue Sherbrooke est, Montréal, QC, Canada, H1X 2B2;(2) Department of Biology, University of Prince Edward Island, 550 University Avenue, Charlottetown, PE, Canada, C1A 4P3 |
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Abstract: | In plant morphology, most structures of vascular plants can easily be assigned to pre-established organ categories. However,
there are also intermediate structures that do not fit those categories associated with a classical approach to morphology.
To integrate the diversity of forms in the same general framework, we constructed a theoretical morphospace based on a variety
of modalities where it is possible to calculate the morphological distance between plant organs. This paper gives emphasis
on shoot, leaf, leaflet and trichomes while ignoring the root. This will allow us to test the hypothesis that classical morphology
(typology) and dynamic morphology occupy the same theoretical morphospace and the relationship between the two approaches
remains a question of weighting of criteria. Our approach considers the shoot (i.e. leafy stem) as the basic morphological
structural unit. A theoretical data table consisting of as many lines as there are possible combinations between different
modalities of characters of a typical shoot was generated. By applying a principal components analysis (PCA) to these data
it is possible to define a theoretical morphospace of shoots. Typical morphological elements (shoots, leaves, trichomes) and
atypical structures (phylloclades, cladodes) including particular cases representing ‘exotic’ structures such as the epiphyllous
appendages of Begonia and ‘water shoot’ and ‘leaf’ of aquatic Utricularia were placed in the morphospace. The more an organ differs from a typical shoot, the further away it will be from the barycentre
of shoots. By giving a higher weight to variables used in classical typology, the different organ categories appear to be
separate, as expected. If we do not make any particular arbitrary choice in terms of character weighting, as it is the case
in the context of dynamic morphology, the clear separation between organs is replaced by a continuum. Contrary to typical
structures, “intermediate” structures are only compatible with a dynamic morphology approach whether they are placed in the
morphospace based on a ponderation compatible with typology or dynamic morphology. The difference in points of view between
typology and continuum leads to a particular mode of weighting. By using an equal weighting of characters, contradictions
due to the ponderation of characters are avoided, and the morphological concepts of continuum’ and ‘typology’ appear as sub-classes
of ‘process’ or ‘dynamic morphology’. |
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Keywords: | Shoot Model Plant Organs Categories Form |
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