The development of the typical cladomothallus of the red algae Antithaminion plumula (Ellis) Le Jolis [= Pterothamnion plumula (Ellis) Nägcli], (Rhodophyceae, Ceramiales) is simulated with the help of a formal language called L-systems. Two types of uniseriate filaments are distinguished: axial filaments of cladomes with indefinite growth and branching and pleuridia with definite growth and branching. The rythmical acropetal formation of secondary axes with basitonic arrangement contrasts with the intercalary basitonic formation of pleuridia, resulting in an acrotonic arrangement within an (...) axial segment. Five types of cells and two types of cell divisions intervene in the system. In addition, for the graphical representations, some morphological particularities of A. plumula are taken into account: the curvature of axial filaments, the extension of growth zones, variable cell generation times, and segment length variability along an axis. The incidence of these variables on the generated thallus form is emphasized, pointing to the singularities of A. plumula. (shrink)

Plants are considered as archetypes of the ramification phenomenon but numerous elementary processes occur in the elaboration of the shaping of each species. This paper aims to identify the part ascribed to different mechanisms in the morphogenesis of a Thallophyte, the red alga Antihamnion plumula.Agonistic-antagonistic models (Bernard-Weil, 1988) can be applied to this alga whose thallus includes two different kinds of whorls, pleuridian and cladomian. In each whorl the agonistic and antagonistic effects are expressed by the full development (S) of (...) the two branches and by their symmetry rate (R) respectively. Variations in S and R show the existence of particular pleuridian whorls having an intermediary dissymmetry and a rhythmic arrangement similarly to that of the cladomian whorls. A unilateral change of the system (removal of a lateral cladome) induces a transitory destabilisation mainly manifested by the stimulating ascendant flow throughout the thallus. (shrink)