Convergence and parallelism in the evolution of plant metabolism

Convergence and parallelism are contentious terms in evolutionary biology, but both denote essentially a ubiquitous phenomenon: The occurrence of similar phenotypes, in different evolutionary lineages, in a way that cannot be easily reconducted to descent from a shared ancestor. In this article, we trace the historical definitions of the two terms and the current conceptual frameworks to classify instances of repeated evolution, presenting the limits of these approaches in considering convergence and parallelism as a strict dichotomy rather than as part of a continuum along the spectrum of phenotypic similarity. We then present cases of convergence-broadly defined-from plant domestication and specialized metabolism, with the objective of understanding the intricacies between natural selection, constraints and drift underlying the recurrent appearance of complex traits.