Confluence, synnovation, and depauperons in plant diversification

Summary We review the empirical phylogenetic literature on plant diversification, highlighting challenges in separating the effects of speciation and extinction, in specifying diversification mechanisms, and in making convincing arguments. In recent discussions of context dependence, key opportunities and landscapes, and indirect effects and lag times, we see a distinct shift away from single‐point/single‐cause ‘key innovation’ hypotheses toward more nuanced explanations involving multiple interacting causal agents assembled step‐wise through a tree. To help crystalize this emerging perspective we introduce the term ‘synnovation’ (a hybrid of ‘synergy’ and ‘innovation’) for an interacting combination of traits with a particular consequence (‘key synnovation’ in the case of increased diversification rate), and the term ‘confluence’ for the sequential coming together of a set of traits (innovations and synnovations), environmental changes, and geographic movements along the branches of a phylogenetic tree. We illustrate these concepts using the radiation of Bromeliaceae. We also highlight the generality of these ideas by considering how rate heterogeneity associated with a confluence relates to the existence of particularly species‐poor lineages, or ‘depauperons.’ Many challenges are posed by this re‐purposed research framework, including difficulties associated with partial taxon sampling, uncertainty in divergence time estimation, and extinction.ContentsSummary 260 I. Introduction 260 II. Lessons from the literature 261 III. New terms, new possibilities 265 IV. Rate heterogeneity and depauperons 268 V. Obstacles to identifying synnovation, confluence, and depauperons 269 VI. Conclusions 270Acknowledgements 270References 270