A Functionally Integrated Symbiotic System as a Mechanism for Angiosperm Diversification

Akira Yamawo 

Flowering plants have maintained exceptionally high diversity for over 100 million years, yet the mechanisms enabling sustained macroevolutionary diversification remain unresolved. Classical theory predicts a trade-off between speciation and extinction, but angiosperms have repeatedly diversified while persisting across heterogeneous environments. Mutualistic interactions, pollination, seed dispersal, and mycorrhizal symbioses, are widely recognized as key drivers of plant evolution. However, their macroevolutionary roles have largely been examined in isolation, limiting our understanding of how diversification emerges from their combined effects. Here, I propose that angiosperm diversification is better understood as an emergent property of a Functionally Integrated Symbiotic System (FISS), in which multiple mutualisms are organized into a coordinated but functionally asymmetric system. Within this framework, pollination primarily promotes reproductive isolation and lineage splitting, whereas seed dispersal and mycorrhizal symbioses enhance lineage persistence by improving establishment, spatial spread, and tolerance to environmental variability. This functional differentiation effectively decouples processes that promote speciation from those that buffer extinction risk, allowing lineages to both originate and persist. The coordinated action of these mutualisms therefore relaxes the speciation–extinction trade-off and generates positive net diversification over macroevolutionary timescales. By shifting the focus from individual interactions to their configurational integration, this perspective provides a testable framework for understanding angiosperm diversification as a system-level process and highlights the role of ecological interactions as macroevolutionary engines.