Convergent evolution in floral morphology in a plant ring species, the Caribbean Euphorbia tithymaloides

Premise of the Study: Ring species have long fascinated evolutionary biologists for their potential insights into lineage divergence and speciation across space. Few studies have investigated the potential for convergent or parallel evolution along the diverging fronts of ring species. We investigate a potential case of parallel floral variation in the Caribbean spurge Euphorbia tithymaloides, the only plant system with molecular support as a ring species. The terminal populations of each front, despite being the most divergent, exhibit such similar floral traits that were originally considered each other closest relative. Methods: We evaluate convergence in floral and leaf traits in relation to geography across 95 populations spanning the distribution of E. tithymaloides. We also re-analyze available genetic data (from previous phylogenetic analyses) in an explicitly spatial framework. Key Results: Floral morphology appears to have shifted in a convergent fashion along both geographic...