The architectural analysis allowed to distinguish main stages of development of trees. Each of these stages is related with an important event of the plant structural edification. The succession of these stages represents the architectural sequence of the species. Architectural sequence been established for the different species (Cedrus atlantica, Cedrus libani, Pinus halepensis and Pinus brutia). According to this diagrammatic reference, we can use some morphological criteria in order to describe and characterise phenotypic variations due to genetic or environmental factors. The architectural description allowed us to analyse and model the growth (viability of apices, polycyclism, vigour) and branching (distribution of branches, types of branches, sympodial versus monopodial branching) processes on the young tree. Such morphological and mathematical tools are used to discriminate species and some provenances. This methodology allowed to identify criteria to be taken into account in genetic selection programs of tree form in these species and to define the stability and variability of these morphological characters according to ontogenical stage and environmental factors.