A phylogenetic and functional perspective on the origin and evolutionary shifts of growth ring anatomical markers in seed plants

ABSTRACT We reconstruct the evolutionary changes in different anatomical markers in order to understand the evolution and functional aspects of growth rings during the diversification of seed plants (spermatophytes), one of the largest and most diverse lineages of the tree of life. We carried out a wide revision of the anatomy of secondary xylem in spermatophytes and reconstructed the evolution of the different anatomical markers in a time‐calibrated phylogeny. By embodying a functionally and evolutionarily significant concept in growth rings we reveal a new panorama for their frequency and show how common they are in diverse lineages of tropical plants. In this context, the principal anatomical markers of growth rings are identified in the evolutionary history of plants and their association with climate‐related ecological characteristics. We discuss the function of these anatomical markers, especially for thick‐walled and/or radially flattened latewood fibres, fibre zone and dilated rays. Despite the high evolutionary lability of the anatomical markers evidenced by our analyses, they appear to represent deep homologies.