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International audience; Plant architecture strongly influences ecological performance, yet its role in plant evolution has been weakly explored. By testing both phylogenetic and environmental signals, it is possible to separate architectural traits into four categories: development constraints (phylogenetic signal only); convergences (environmental dependency only); key confluences to the environmental driver (both); unknown (neither).We analysed the evolutionary history of the genus Euphorbia, a model clade with both high architectural diversity and a wide environmental range. We conducted comparative analyses of 193 Euphorbia species worldwide using 73 architectural traits, a dated phylogeny, and climate data.We identified 14 architectural types in Euphorbia based on trait combinations. We found 22 traits and three types representing convergences under climate groups; 21 traits and four types showing phylogenetic signal but no relation to climate; and 16 traits and five types with both climate and phylogenetic signals. Major drivers of architectural trait evolution likely include water stress in deserts (selected for succulence, continuous branching), frost disturbance in temperate systems (selected for simple, prostrate, short‐lived shoots) and light competition (selected for arborescence). Simple architectures allowed resilience to disturbance, and frequent transitions into new forms. Complex architectures with functional specialisation developed under stable climates but have low evolvability.

•Broad scale evolutionary comparisons have shown that branching forms arose by convergence in vascular plants and bryophytes, but the trajectory of branching form diversification in bryophytes is unclear. Mosses are the most species rich bryophyte lineage and two sub-groups are circumscribed by alternative reproductive organ placements. In one, reproductive organs form apically, terminating growth of the primary shoot (gametophore) axis. In the other, reproductive organs develop on very short lateral branches. A switch from apical to lateral reproductive organ development is proposed to have primed branching form diversification. •Moss gametophores have modular development and each module develops from a single apical cell. Here we define the architectures of 175 mosses by the number of module classes, branching patterns and the pattern in which similar modules repeat. Using ancestral character state reconstruction we identify two stages of architectural diversification. •During a first stage there were sequential changes in the module repetition pattern, reproductive organ position, branching pattern and number of module classes. During a second stage, vegetative changes occurred independently of reproductive fate. •The results pinpoint the nature of developmental change priming branching form diversification in mosses and provide a framework for mechanistic studies of architectural diversification.

International audience; There is a growing interest for methods in plant biology that summarize different plant growth forms and which can identify patterns of growth form variability at ecological scale in a global context. The use of detailed architectural descriptions can bring valuable information for understanding what developmental features underlie the transitions from one growth form to another. In this paper, we investigate the developmental attributes responsible for growth form variation in Thymus vulgaris and whether they are linked to habitat preference. We analysed architectural development in T. vulgaris from 12 populations in southern France, which includes two contrasting habitats of the species. Architectural development in T. vulgaris is based on three hierarchical levels of organization, which include the module, the branched complex and the whole plant. T. vulgaris is found as three different growth forms that can vary from basally branched to more apically branched growth forms. Differences in growth form result from variations in the sequential repetition of branched complexes and are also linked to the type of habitat. Individuals growing in hot, dry, rocky habitats are dominated by plants that display mostly a basally branched (basitonic) architecture – a potentially adaptive architectural trait for exploiting space in open woodland. Individuals growing in colder, more humid habitats that are dominated by tall grasses display mostly apically branched (mesotonic and acrotonic) architectures resulting in more elevated growth forms. The architectural method provides additional insight into how variations in form are developed in small-bodied woody plants such as Thymus. We found that reiteration processes are important for forming different organisational levels and variations in growth form. Architectural traits provide additional markers for ecological studies that wish to understand how living space is exploited by the whole plant. The study represents a promising approach for identifying whole plant traits at the community level.

International audience; Plant architecture is related to the performance of long-lived plants; its role in promoting species coexistence and in successional patterns is now widely recognized. However, because plant architecture involves branching processes, it is highly variable at the intra-specific level. In this paper, we address two questions: what is the best way to describe plant architecture to obtain meaningful information for explaining population cover: at the whole-plant level, or at the level of its unitary constituent parts? Further, are there architectural designs related to populations’ success? We evaluated the relative impact of ontogeny and whole-plant traits on the cover achieved by the populations of five shrub species developing on 25 abandoned farmlands in southwestern Québec (Canada). We compared four ways of analyzing plant architecture: 1–2) using morphological traits described at the scale of a module (an elementary architectural unit made up of all the different types of shoots), with or without taking into account the ontogeny of the whole organism, 3) using the rate of changes during ontogeny as traits, and 4) using whole-plant traits describing branching processes at a scale larger than modules. We then used variation partitioning to discriminate the actual effects of these traits on percent cover of the species from hidden effects due to plant ontogenesis and population spatial structure. Our results suggest that the predominant variables that effectively describe population cover vary from one species to another. At the same time, whole-plant architectural traits and the rate of change of morphological traits during ontogeny both have an important effect on population cover. These findings suggest that acknowledging the developmental pattern of woody species can clarify the impact of intra-specific trait variation on population cover

Canada yew (Taxus canadensis Marsh.) is a clonal species with two types of ramets. The most common type has bilateral symmetry and alternate branching. The radial symmetry and opposite branching of the rarer type are similar to the architecture expressed in a young plant grown from seed. Architectural analysis was conducted on four colonies of increasing age and size. A genetic analysis using random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) was conducted on 122 ramets, 93 sampled from nine colonies from a single population, 24 from eight other populations, and five from other Taxus species. Analysis of the architectural development sequence shows that yew follows the same architectural model as, for example, species of Abies or Picea. This model constitutes a level of organization intermediate between that of the ramet and of the genet. The molecular analyses confirm the greater variability of AFLPs over RAPDs and indicate that architecture is not directly related to genotypic variation. Ramets with radial symmetry have slightly higher genetic variation, on average, than ramets with bilateral symmetry with 95% degree of confidence. The molecular analyses show that the level of resolution of the AFLPs is adequate to characterize 98% of the ramets of a colony. Between pairs of physically connected ramets, some random genotypic differences are observed, supporting the hypothesis of genetic mosaicism in plants, due to somaclonal variations.Key words: architecture, clonal plant, intraclonal variation, molecular markers, somaclonal mutations.

The maximal architectural development of a modern maize cultivar (Zea mays L. ‘Dea’) was studied in fully isolated and carefully irrigated plants. Under these favourable conditions, this (usually) non-tillering and non-prolific cultivar displayed a large amount of branching (down to the third order), including large basal tillers and prolific ear shoots. This development was analysed by combining: (1) architectural analysis, initially developed for trees; and (2) quantitative analysis of tillering kinetics, designed for other grass species. The architectural unit of maize included a main long axis (A1) and lateral short shoots bearing a terminal spike (A2). The basal tillers (noted A1«) resulted from a complete and sylleptic reiteration. Its kinetics were consistent with tillering models, but with a particularly long delay in branch emergence (seven phyllochrons), compared to other grass species. This delay is likely to enhance regulation by leaf (or root) density in stands and explains the inhibition of branch development, as usually observed in field conditions, even at low density. Similarly, the suppression of the basal reiteration in secondary branches observed in isolated plants probably results from increased intra-tussock density. In isolated plants, androgenous axes combining A1« and A2 morphologies were also produced in intermediate positions. It is shown that they can result from a basipetal sequence of A2 dierentiation reaching buds in the course of their A1« development. The consequences of these unexpected results are discussed in terms of maize development and architectural analysis of grasses. # 1999 Annals of Botany Company

The architectural analysis of trees, as developed since the pioneering work of Halle & Oldeman in the 1960s and 1970s, allows the study of the developmental pattern characteristic to each species i...

Four tree species of the temperate deciduous forests of south-western Québec have an architectural development that corresponds to Troll's model. Two of these species, American elm (Ulmus americana L.) and American basswood (Tilia americana L.), are mid-successional and the two others, American beech (Fagus grandifolia Ehrh.) and Eastern hemlock (Tsuga canadensis (L.) Carr.), are late successional. In the four species, the main stem is the result of the stacking of modules with plagiotropic development and secondary straightening. Nevertheless, the architectural analysis of these four species reveals that two growth patterns are present. In elm and basswood, the modules are differentiated from one another and are integrated into the hierarchical structure of the tree. In beech and hemlock, the modules are mixed and their apical meristems possess an autodifferentiation potential, which provides for a greater individuality within the tree structure. In spite of belonging to the same architectural model, differences in the development pattern favour a greater efficiency in stem growth for elm and basswood versus a greater shape plasticity, including a greater lateral branch development if required, in beech and hemlock.Key words: tree architecture, organization plan, Troll's model, plagiotropy, morphological differentiation of axes.

Plant succession is a phenomenon ascribed to vegetation dynamics at the scale of the plant community. The study of plant succession implies the analysis of the species involved and their relationships. Depending on the research done, the characteristics of trees have been studied according to either static, dimensional or partial approaches. We have revised the principal theories of succession, the methods of describing structure and development of tree and relationship established between tree species' attributes and their successional status. During studies of succession, we propose that the profile of plant species be completed by including the organizational attributes of their structure as well as their development dynamics. We suggest an approach to the architecture that gives a general overview of the mode of development, revealing, among other things, that a limited number of architectural models may be found in nature. We hypothesize that community dynamics, in succession, may to a certain degree arise from the dynamic nature of plant development. This line of reasoning is in accordance with the current school of thought on process structuralism.

Summary Morphological study of the Plane tree shows that the root system of this species has a completely sympodial structure. The layout of root sympodial units leads to a pseudomonopodial organization, never been observed in roots. The endogenous origin of this sympodial development is discussed. Abridged version Different works show us the occurence of sympodial branching in roots (Gill and Tomlinson, 1977; Oldeman, 1990). Usually, this type of branching is considered as a resuH of injury which accidentally destroy apical meristem (Wilson, 1970). Thus, analysis intended to understand structure and development of plane tree root system (Platanus hybrida Brat. Platanaceae) lead us to revise this interpretation. We made our observations in natural habHat near Montpellier in the South of France. We have completely freed root systems of thirty individuals from seedlings to aduHs developing Hs first main orthotropic branches. For each individual, we have described the morphology of each root taking in accoun...

Since 1970, the architectural analysis of woody plants has given much information about structural and functional organization of tree crowns, their development, and reiteration patterns. In this study, we have extended this method to tree root systems. We describe the whole architecture of three species and we compare their root system and crown architectural patterns. Key words: architecture, tree, root system, crown, whole plant.

A-10-02; International audience; Background and Aims: Qualitative and quantitative studies of the pattern of invasive plant development is considered a key aspect in understanding invasiveness. An architectural analysis was therefore performed in order to understand the relationship between shoot architecture and invasiveness in red-osier dogwood, Cornus sericea (Cornaceae). Methods:The structural and ontogenic characteristics of individuals in invading and non-invading populations in the native range of the species were compared to test the implication of developmental plasticity on invasiveness. Key Results and Conclusions: The results show that the shrub has a modular architecture governed by strong developmental rules. Cornus sericea is made up of two levels of organization, each with its own intrinsic sequence of differentiation. These intrinsic mechanisms were used as a framework for comparison and it was found that, in response to the light environment, developmental plasticity was elevated, resulting in two architectural strategies. This developmental plasticity concerns the growth direction and the size of the modules, the speed of their time-course changes, their branching and flowering. Under an open canopy, C. sericea rapidly develops large vertical structures and abundant flowering. This strategy leads the plant to be invasive by excluding competitors and disseminating in the landscape. In the understorey, C. sericea slowly develops long horizontal structures which creep across the soil surface, while assimilating structures are poorly developed. This strategy does not lead to invasiveness but may allow the plant to survive in the understorey and reach sunny patches

National audience; Species identification is a major constraint for biodiversity conservation.Conventional identification tools are usually difficult to use for non specialists, mainly because they require important botanical knowledge during the identification process. For this reason, we developed a graphical identification approach that resulted in the IDAO (IDentification Assistée par Ordinateur) software. Through simple clicks on vector drawings, the user selects morphological (shape, size, position, color and texture of organs) or ecological characters corresponding to the plant he/she wants to identify, thus building a sort of “identikit picture” for the species. The software compares this set to all those available in its database with a simple matching coefficient, and provides a probable identification. At any time during the process, the user may consult species description files. Missing information is tolerated, users can thus access to a result of their identification, without the use of all characters of identification. Numerous illustrations are present in each species description in order to facilitate identification.This graphic multi-entry identification system has been adapted to various floras (weeds, trees, orchids) around the world (West Africa, India, Cambodia, etc.), for weed control or biodiversity conservation. It is accessible on-line on Internet (http://umramap.cirad.fr/amap2/logiciels_amap/index.php?page=idao), or available on Cd-rom. Current developments on the new version of this identification tool include (i) a free open version, which will allow adaptation of the graphic interface by users according to their own flora, (ii) generalisation of the use of open drawing format (SVG: Scalable Vector Graphics), (iii) the extension of this approach to new characters (such as anatomical characters of the wood), and floras (such as paddy fields weeds). There is no constraint for the use of this tool for the identification of animal species; it wasn't realized however until today.

National audience; Species identification is a major constraint for biodiversity conservation. Conventional identification tools are usually difficult to use for non specialists, mainly because they require important botanical knowledge during the identification process. For this reason, we developed a graphical identification approach that resulted in the IDAO (IDentification Assistée par Ordinateur) software. Through simple clicks on vector drawings, the user selects morphological (shape, size, position, color and texture of organs) or ecological characters corresponding to the plant he/she wants to identify, thus building a sort of “identikit” for the species. The software compares this set to all those available in its database with a simple matching coefficient, and provides a probable identification. At any time during the process, the user may consult species description files. Missing information is tolerated, and users can thus access to an identification result without needing to use all characters in the set. Numerous illustrations are present in each species description file in order to facilitate identification.This graphic multi-entry identification system has been adapted to various floras (weeds, trees, orchids) around the world (West Africa, India, Cambodia, etc.), for weed control or biodiversity conservation. It is accessible on-line on Internet (http://umramap.cirad.fr/amap2/logiciels_amap/index.php?page=idao), or available on CD-ROM. Current developments for the new version of this identification tool will include (i) a free open version, which will allow adaptation of the graphic interface by users according to their own flora, (ii) generalisation of the use of open drawing format (SVG: Scalable Vector Graphics), (iii) the extension of this approach to new characters (such as anatomical characters of the wood), and floras (such as paddy fields weeds).

A-09-11; International audience; Architectural descriptors were used to understand root system structure and development in white yam (Dioscorea rotundata Poir., Dioscoreaceae), a tuber monocot. Observations were made on seedlings and plant derived from tuber fragments, cultivated in greenhouses over a developmental cycle. This study demonstrated that both seedlings and plants derived from tubers have two distinct root systems that are highly organized. The first (seminal or tubercular) has been called the temporary root system which is small and short lived. The architectural unit here is made up of two root axis categories. The second (adventitious in both cases) has been called the definitive root system. It is larger and has a far longer lifespan than temporary root systems. The architectural unit here is made up of three root axis categories. Adventitious root systems are formed by structural repetitions of their own architectural unit. The temporary and definitive root systems possess the same structural and functional properties and become established and succeed one another in time following an identical developmental sequence. Neo tuber development is coupled with the root system development. Our results highlight to what extent it is important to study simultaneously the different parts of a root system in order to understand its development. This study confirms how architectural tools can be used to understand root system structure and development and prove accurate informations on root system development for use in agricultural management.

International audience

ResumeA l'aide de la methode architecturale nous donnons une description du developpement complet de Platanus hybrida Brot. L'analyse architecturale fait ressortir une organisation monopodiale tres forte malgre un fonctionnement sympodial. Ainsi il y a construction d'un tronc et de branches par la succession lineaire de modules annuels. La cime du Platane est edifiee par un phenomene de reiteration precede d'une veritable metamorphose architecturale. Le caractere sympodial semble etre une des causes de son extraordinaire reponse aux pratiques culturales. La suite et les differentes orientations de l'etude sont envisagees dans le cadre de la gestion du platane en milieu urbain (elegages, contraintes).

Since 1986, the sterile populations of the laurel fig, Ficus microcarpa L., in Tunisia have become fertile with the arrival of the species-specific pollinating wasp Parapristina verticillata. However, the invasion in 1992 by one of several species-specific parasitic wasps, Odontofroggatia galili, has changed the parameters of this mutualistic relationship. A fig sample collected at Sfax, Tunisia, was analysed, and randomization of the results showed a highly significant negative correlation between the numbers of wasps and parasites. Moreover, the presence of parasites decreases the fecundity of the figs. The consequences of the competition between O. galili and P. verticillata on this fig – fig pollinator mutualism are discussed.

Some results of the application of the method of architectural analysis, originally designed for trees, to crop species are reviewed. They are illustrated through a comparison between two species, maize (Zea mays L.) and pea (Pisum sativum L.). It is shown that despite huge apparent differences in physiognomy, similarities in architectural development can be found, and expressed within the framework of architectural analysis. The relevance of these results for architectural modelling, crop ecophysiology and architectural studies is discussed. It is argued that one of the main benefits of an interdisciplinary approach probably is at the inter-specific comparative level, and that it may allow for the development of rather general structure-function architectural models, with a clarification of significant specific traits. (© Inra/Elsevier, Paris.), Cet article présente une illustration des premiers acquis de l’application de l’analyse architecturale, initialement développée pour les ligneux, à des espèces herbacées cultivées, à partir de la comparaison de deux espèces, le maïs (Zea mays L.) et le pois (Pisum sativum L.). Malgré d’évidentes différences physionomiques, des similitudes de développement architectural, correspondant à des concepts d’analyse architecturale, existent. La signification de ces résultats pour la modélisation architecturale, l’agrophysiologie et l’architecture des plantes sont discutées. Il semble que le principal bénéfice d’une telle approche interdisciplinaire réside dans la mise en place d’une écophysiologie développementale comparée (entre espèces). Ceci devrait permettre le développement de modèles structure-fonction architecturaux assez généraux, avec une meilleure identification des caractéristiques spécifiques. (© Inra/Elsevier, Paris.)

Les forets heterogenes guyanaises sont des milieux complexes dont la gestion passe par la comprehension de leur organisation (structure spatiale, horizontale et verticale et diversite specifique) et de leur dynamique. Dans ce contexte, l'etude des strategies de developpement et d'occupation de l'espace des arbres permet de mieux comprendre comment les differentes especes exploitent et structurent l'heterogeneite du milieu. Depuis une trentaine d'annees, les travaux menes en architecture vegetale ont permis d'etablir un contexte methodologique et conceptuel pour etudier la structure globale de l'arbre et pour comprendre les mecanismes morphologiques qui lui ont donne naissance. Apres une presentation de concepts majeurs d'architecture vegetale, cet article expose les methodes employees pour quantifier la structure des arbres et les approches permettant d'integrer les criteres architecturaux dans un diagnostic a l'echelle du peuplement.

ResumeLes, especes actuelles de Coniferes se developpent conformement aux modeles de RAUH, MASSART, ATTIMS et MANGENOT. Cependant, les modalites, particulierement nuancees, de l'expression de la plagiotropie conduisent souvent a des architectures intermediaires entre plusieurs modeles. Cette originalite est peut-etre liee au caractere archaique de ce taxon.

Some very impressive results have been obtained in the past few years in plants and trees image synthesis. Some algorithms are largely based on the irregularity and fuzziness of the objects, and use fractals, graftals or particle systems. Others focus on the branching pattern of the trees with emphasis on morphology. Our concern here is the faithfulness of the models to the botanical nature of trees and plants. We present a model which integrates botanical knowledge of the architecture of the trees: how they grow, how they occupy space, where and how leaves, flowers or fruits are located, etc. The very first interest of the model we propose is its great richness: the same procedural methods can produce "plants" as different as weeping willows, fir trees, cedar trees, frangipani trees, poplars, pine trees, wild cherry trees, herbs, etc. Another very important benefit one can derive from the model is the integration of time which enables viewing the aging of a tree (possibility to get different pictures of the same tree at different ages, accurate simulation of the death of leaves and branches for example). The ease to integrate physical parameters such as wind, the incidence of factors such as insects attacks, use of fertilizers, plantation density, and so on makes it a useful tool for agronomy or botany.

Les recherches effectuees depuis une quinzaine d'annees sur l'architecture et la dynamique de croissance des arbres permettent de decrire leur developpement de la germination jusqu'a la mort. En retracant l'ensemble des formes que l'organisme vegetal presente au cours de son developpement, elles ont conduit a degager les principales lois qui president a leur croissance et ont contribue a la creation d'un logiciel capable de simuler le developpement de l'arbre dans le temps et l'espace. L'objet de cet article est de faire une presentation d'ensemble de ces travaux en insistant sur l'interet potentiel de l'outil informatique dans la conception et la gestion de l'espace urbain

A l'aide des concepts de modèle architectural et de réitération, les études architecturales peuvent contribuer à améliorer les connaissances sur le phénomène de vieillissement des arbres en analysant et en décrivant les processus morphogénétiques successifs intervenant depuis la mise en place de la couronne jusqu'à la mort de l'arbre. Les trois types principaux d'événements architecturaux de cette période sont décrits

Le but de ce travail est de presenter un modele de developpement des plantes base sur la mesure des caracteristiques d'arbres individuels. Ce modele informatise et associe a des procedes graphiques perfectionnes fournit une representation de la croissance et de l'architecture d'une large gamme de plantes

L'architecture d'une plante depend de la nature et de la disposition relative de ses differentes parties; elle est, a chaque instant, l'expression d'un equilibre entre le processus de croissance endogene et les contraintes exogenes exercees par l'environnement. Le but de l'analyse architecturale est d'identifier ces processus endogenes. Pour chaque espece et chaque stade de developpement, des observations sont effectuees sur un nombre variable d'individus en fonction de la complexite de l'architecture etudiee. Les resultats sont ensuite reportes sur des diagrammes qui symbolisent les stades successifs de croissance. La validite de ces diagrammes est verifier par comparaison avec la croissance reelle des plantes et ils doivent s'appliquer a n'importe quel individu de l'espece consideree pour que l'analyse soit consideree comme complete

The plants growth forms have been studied many times but they still represent nowadays a fuzzy set, often modified because of the inconsistency and the heterogeneity of the methods used in their analysis. This lack of precision often leads to an inconsistency of the use of the growth forms as a trait in the studies of plants communities and their dynamics. We tried to remedy this situation by applying to some of them the architectural analysis initiated by Hallé and Oldeman, which has been relevant for the understanding of the tree growth form.This study aimed to 1) interpret these growth forms terms and their variability in architectural terms, 2) study architectural traits variation within roadsides plants communities during succession and in a mowing context. Our results show that 1) the architectural concepts and traits are also applicable to non-arborescent growth forms, 2) the expression of the reiteration is the main source of structural variation of growth forms at specific and intraspecific levels and 3) that traits values are changing during succession within the communities : Plants living at early successional stages got a simple architectural unit and reiterate at the base of the individual while plants living at late successional stages got complex architectural unit and can produce acrotonic reiteration. These results lead us to discuss the holistic value of the architectural analysis for growth forms characterization, of biological processes allowing for growth form variation and the interest of the use of architectural traits in plant communities studies.; Les formes de croissance végétales ont fait l'objet de nombreuses études mais elles constituent encore aujourd'hui un ensemble mal défini et sans cesse remis en question en raison de l'incohérence et de l'hétérogénéité des méthodes employées pour les analyser. Cette imprécision a des répercussions négatives lorsque les formes de croissance sont utilisées dans l'étude des communautés végétales et de leur dynamique. Nous avons tenté de remédier partiellement à cette situation en appliquant à certaines d'entre elles la méthode d'analyse architecturale initiée par Hallé et Oldeman dont l'efficacité s'est avérée remarquable pour la compréhension des formes arborescentes. L'étude était destinée 1) à interpréter ces formes de croissance et leur variabilité à l'aide des concepts architecturaux, 2) à suivre les changements des traits architecturaux au sein d'une communauté végétale se développant sur des talus, lors d'une chronoséquence et en fonction de différents gradients environnementaux.Nos observations montrent que 1) les concepts et les traits architecturaux sont applicables aux formes de croissance herbacées, suffrutescentes, et buissonnantes, 2) l'expression de la réitération est la source principale de variation structurale des formes de croissance aussi bien à l'échelle spécifique qu'infra-spécifique, 3) la valeur des traits architecturaux change au cours de la succession au sein de la communauté : les plantes vivant sur des talus jeunes ont une unité architecturale simple et réitèrent à la base alors que celles croissant sur des talus plus anciens ont des unités architecturales complexes et réitèrent de manière acrotone. Ces résultats nous conduisent à discuter de la valeur holistique de la méthode d'analyse architecturale pour la caractérisation des formes de croissance, des processus biologiques permettant de passer d'une forme de croissance à une autre et de l'intérêt pratique de l'utilisation des traits architecturaux dans l'étude des communautés végétales.

L’étude qualitative et quantitative du mode de développement des plantes envahissantes est actuellement considérée comme une étape clef dans la compréhension des phénomènes d’invasion. L’objectif de ce travail est de préciser les relations qui existent entre la structure architecturale des buissons et leur caractère proliférant. Nous avons sélectionné cinq espèces buissonnantes (Cornus sericea L., Cornaceae ; Prunus virginiana L., Rosaceae ; Rhamnus cathartica L., Rhamnaceae ; Rhus typhina L., Anacardiaceae ; Zanthoxylum americanum Mill., Rutaceae) qui sont connues pour leur aptitude à bloquer la succession végétale sous certaines conditions au Sud du Québec (Canada). L’analyse architecturale a permis chez ces espèces de caractériser les unités structurelles et leurs modifications ontogéniques. Ces modifications ontogéniques doivent être prise en compte afin d’obtenir une description complète de la plasticité phénotypique chez ces espèces. L’analyse des différentes unités structurelles révèle qu’elles ne possèdent pas la même signification fonctionnelle : les niveaux d’organisation les plus grands sont responsables majoritairement des capacités de plasticité phénotypique de la plante et de sa compétition. Ces analyses ont abouti à la définition de trois stratégies architecturales correspondant à des comportements individuels et qui sont également pertinentes pour expliquer la prolifération des populations., Qualitative and quantitative studies of the pattern of invasive plant development is now considered a key aspect in understanding invasiveness. This work was performed to determine relationships between shrub architectural plasticity and proliferating behaviour. We selected five shrub species (Cornus sericea L., Cornaceae ; Prunus virginiana L., Rosaceae ; Rhamnus cathartica L., Rhamnaceae ; Rhus typhina L., Anacardiaceae ; Zanthoxylum americanum Mill., Rutaceae) known to arrest plant succession under certain conditions in Southern Québec, Canada. Architectural analysis revealed species’ structural units and their ontogenic changes. These ontogenic changes need to be calibrated if a full description of phenotypic plasticity is to be obtained. Analysis of the plant structural units reveals that they are of different functional significance: the higher the level of organization, the greater the capacity for phenotypic plasticity and competition. We defined three architectural strategies related to individual behaviours and which can relevantly explain the population proliferation of shrubs., Réalisé en cotutelle avec l'Université Montpellier II

Qualitative and quantitative studies of the pattern of invasive plant development is now considered a key aspect in understanding invasiveness. This work was performed to determine relationships between shrub architectural plasticity and proliferating behaviour. We selected five shrub species (Cornus sericea L., Cornaceae ; Prunus virginiana L., Rosaceae ; Rhamnus cathartica L., Rhamnaceae ; Rhus typhina L., Anacardiaceae ; Zanthoxylum americanum Mill., Rutaceae) known to arrest plant succession under certain conditions in Southern Québec, Canada. Architectural analysis revealed species' structural units and their ontogenic changes. These ontogenic changes need to be calibrated if a full description of phenotypic plasticity is to be obtained. Analysis of the plant structural units reveals that they are of different functional significance: the higher the level of organization, the greater the capacity for phenotypic plasticity and competition. We defined three architectural strategies related to individual behaviours and which can relevantly explain the population proliferation of shrubs.; L'étude qualitative et quantitative du mode de développement des plantes envahissantes est actuellement considérée comme une étape clef dans la compréhension des phénomènes d'invasion. L'objectif de ce travail est de préciser les relations qui existent entre la structure architecturale des buissons et leur caractère proliférant. Nous avons sélectionné cinq espèces buissonnantes (Cornus sericea L., Cornaceae ; Prunus virginiana L., Rosaceae ; Rhamnus cathartica L., Rhamnaceae ; Rhus typhina L., Anacardiaceae ; Zanthoxylum americanum Mill., Rutaceae) qui sont connues pour leur aptitude à bloquer la succession végétale sous certaines conditions au Sud du Québec (Canada). L'analyse architecturale a permis chez ces espèces de caractériser les unités structurelles et leurs modifications ontogéniques. Ces modifications ontogéniques doivent être prise en compte afin d'obtenir une description complète de la plasticité phénotypique chez ces espèces. L'analyse des différentes unités structurelles révèle qu'elles ne possèdent pas la même signification fonctionnelle : les niveaux d'organisation les plus grands sont responsables majoritairement des capacités de plasticité phénotypique de la plante et de sa compétition. Ces analyses ont abouti à la définition de trois stratégies architecturales correspondant à des comportements individuels et qui sont également pertinentes pour expliquer la prolifération des populations

Th-97-01; This study give a global vision of the beechtree development. This study is a descriptionof the beech architectural development from the seed to the death plant in various environments. Thisstudy has allowed to propose or precise some hypothesis about the signification of certain beechdevelopment phases. The edification of the architectural unit is the edification of a hierarchic branchingsystem more and more élaboré, constituated of longer and more branched growth units, but also growthunits which, for a given lenght, (i) bear more leaves, bigger et thicker leaves, (ii) have more xylem and morephloem for conduction of sap flow - many elements which seem contribuate to increase the plantpotentialities. The end of the differenciation corresponds to the reaching of the meristematic functionnallimits of the plant. This stop of the growth unit differenciation seems induce in the plant the gradual transitionfrom an hiérarchic organization to a polyarchic organization.The beech architectural study confirme also thelimits between the different reiteration modalities. The sylleptic réitération, duplication phenomenon, notintegrate rejuvenation and there is continuity during development phase.The proleptic réitération integraterejuvenation phenomenon and there is discontinuity beetwen sequential and proleptic structures (here theepicormic shoots).; Ce travail propose une vision globale du développement du hêtre. Il se traduit par unedescription du développement architectural du hêtre depuis le stade de la graine jusqu'à la mort de laplante dans différents environnements. Cette étude a permis d'émettre et de préciser certaineshypothèses à propos de la signification de certaines phases du développement du hêtre. L'édification del'unité architecturale correspond à la mise en place d'un système caulinaire hiérarchisé de plus élaboré,constitué d'unités de croissance plus longues, plus ramifiées, mais aussi des u.c. qui, pour une longueurdéfinie, portent plus de feuilles, des feuilles plus grandes, plus épaisses, renferment plus de xylème et dephloème facilitant le transport des sèves brutes ou élaborées - Autant d'éléments qui semblent contribuer àaccroître les performances de la plante. Le terme de cette différenciation correspond à l'atteinte des limitesfonctionnelles des méristèmes de la plante. Cet arrêt de la différenciation des unités de croissance semble àl'origine de la transition graduelle de la plante d'un mode d'organisation faisant intervenir des complexesréitérés. L'analyse architecturale du hêtre confirme également le clivage existant entre les différentesmodalités de réitération. Le processus de réitération immédiate, phénomène de duplication, n'intègre pasde phénomène de rajeunissement et il y a continuité de la séquence de développement des structurescaulinaires lors de la transition d'une phase de développement à l'autre. En revanche, Le processus deréitération différée intègre des phénomènes de rajeunissement qui expriment une discontinuité entre ladifférenciation des structures caulinaires séquentielles et celles de structures tardives (rameauxépicormiques).