Architecture and development sequence of Araucaria araucana in natural forests of Argentina

The architecture and sequence of development of #Araucaria araucana# in the natural forests of western Neuquén province (Argentina) are described here by means of the concepts and method of architectural analysis. The architecture of a particular plant species is characterized by the nature and relative position of each of its axes. The study of plant architecture requires the analysis of different morphological features (such as the patterns of growth and branching, the position of sexuality and the morphological differentiation of the axes) in a number of individuals at each of the developmental stages of the species. The elementary architecture of #A. araucana# (i.e. its architectural unit) is composed of three categories of axes, among which there is a strong hierarchy. The sequence of development in the understorey is very slow. It is characterized by long periods of rest at the main stem apex, which looses the apical dominance, and by a slow increment in both the number of branches per branch tier and the number of tiers of living branches on the main stem. The architectural unit in reached when sexual structures are developed on third-order axes (twigs). All kinds of reiterations (i.e. duplications of the elementary architecture) may be formed along the sequence of development of #A. araucana# (Résumé d'auteur