Classical and dynamic morphology: toward a synthesis through the space of forms

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'.

Durianology, discovery, and saltation — the evolution of aroids

“…The (transmodernist, 'systems') idea of phenes being recognisable but integrated, on the other hand, accords with the reality of differential evolution, but would reject disassociation. In principle there is a spectrum from phenes in lockstep to phenes in which change has almost no impact on certain other morphogenetically 'distant' phenes, but which are still only quasi-independent: morphological subunits are not merely juxtaposed to make the whole shoot-unit, but 'encased' within it (see Jeune et al, 2006). The phene is thus perhaps only meaningful syntactically in a top-down context of the development of the whole, and its 'individual' evolution is only comprehensible in the top down context of the evolution of the whole, constrained by, among other things, the nature of prototypes at nearer and further levels in the taxonomic hierarchy.…”

“…Earlier I stressed the ease with which 'character evolution' can slide into nonsense, by highlighting a couple of examples where the evolution of the features concerned is necessarily contextual in reality, and which constitute largely meaningless 'busy work' when conceptualised as characters 'evolving' in vacuo. A further clue to the direction this should take is provided by Jeune et al (2006) noting that, holistically speaking, morphological subunits are not juxtaposed (in the shoot) but 'encased' by it. While leaves, for example, are encased by the shoot, the leaf in turn encases orders and patterns of venation and other subordinate characteristics.…”

Unusual developmental morphology and anatomy of vegetative organs in Utricularia dichotoma—leaf, shoot and root dynamics

“…modalities, parameters, or variables; see Table 3), the principal component analysis (PCA) was applied, largely following Jeune and Sattler (1992). In contrast to the PCA of Jeune et al (2006), who centred the data Merl (1915) also uses the term root-leaf ('Wurzelblatt') set on the 'theoretical shoot' (focussing on the partialshoot concept of all organs) and excluded roots, we included all basic organ categories (shoot, leaf and root) without centring any of them. Whilst Sattler and Jeune (1992) and Jeune et al (2006) selected representative species for typical structures, we followed Jeune and Sattler (1992) and used a larger variety of a typical (although theoretical) root, shoot and leaf in angiosperms with a broader range of possible combinations of modalities per organ type (see Table 4), leading to larger areas of the organ types in the morphospace.…”

“…shall be answered for all vegetative organ types of U. dichotoma in this paper by applying the mathematical approach of the principal component analysis (PCA) in the concept of dynamic/process morphology following, e.g. Jeune and Sattler (1992) and Jeune et al (2006). This method enables a visualization of correlations (and distances) between plant structures and groups of organs in the morphospace based upon developmental processes (Kirchoff et al 2008).…”

Rethinking hybridity: Interrogating mixedness

“…What this means in the world of plants is that a feature of a plant such as a leaf, as well as where that leaf appears and what it does, is potentially insecure; a lively and unfolding 'process combination' where a leaf can be partially or wholly replaced by an axillary shoot, that may or may not correspond in its functioning as a leaf, that is, as an organ of photosynthesis (see Jeune et al, 2006;Hirayama et al, 2007). Crucially, Sattler notes, the assumed continuum is heterogeneous and dynamic, similar to Delanda's (2002) 'state space' that both plays host to and is a vital part of the process of interrelations.…”