Vascular plant reproductive structures have become more complex through time, evolving differentiated parts that interact in specialized ways. But quantifying these patterns at broad scales is challenging because lineages produce disparate reproductive structures that cannot readily be compared. We develop a novel approach for analyzing interactions within reproductive structures using networks, treating component parts as nodes and a suite of physical and functional interactions among parts as edges. We apply this approach to the plant fossil record, showing that interactions have generally increased through time and that the concentration of these interactions has shifted towards differentiated surrounding organs, resulting in more compact, functionally integrated structures. Such transference of function and morphological differentiation are widespread across plant lineages, but their extent and timing vary with reproductive biology; seed-producing structures show them more strongly than spore or pollen-producing structures. More broadly, our results demonstrate that major reproductive innovations like the origin of seeds and angiospermy were associated with increased integration and interactions among parts. However, they also reveal that for certain lineages, such as Mesozoic gymnosperms, millions of years elapsed between the origin of a reproductive innovation and a measurable increase in the integration and interaction among parts within their reproductive structures.

R; Python