Gymnosperms – A forgotten model for phyllotaxis research

Abstract

Phyllotaxis, the regular arrangement of lateral organs initiated at the shoot apical meristem (SAM), has long served as a model for studying pattern formation in plants. Gymnosperms, due to their crystal-like organ arrangements, suitable for geometric analyses, were often used in phyllotactic research. In addition, the interrelationship between phyllotaxis and the primary vascular system became well-recognised. Here, we review classical morphological and anatomical data together with recent molecular findings to reevaluate gymnosperms as a model system for phyllotaxis regulation. We discuss the diversity and ontogenetic dynamics of phyllotactic patterns, their close relation with SAM structure and activity and the role of the vascular system as a potential constraint stabilising pattern propagation and chirality. Available evidence suggests that auxin-dependent mechanisms are evolutionarily conserved, but operate within diverse structural contexts. We propose that integrating classical datasets with modern experimental and modelling approaches, applied to gymnosperms, can reveal fundamental principles governing phyllotaxis regulation.