A collaborative effort involving Wilson and environmental scientists from Yale, Bates, The University of Maine, and The Czech Academy of Sciences suggests that resistance to drought rather than structural support drove plants’ structural diversification as they adapted to survive amid their new surroundings. The study’s implications suggest that even the slightest environmental changes create a reverberating—and harmful—effect on an ecosystem.

The paper draws on three lines of evidence—mathematical modeling, paleobotany, and experimental analysis of living plants—to demonstrate that the anatomical forms found in the fossil record, and the sequence that they are found in, is explained by evolutionary selection for plants resisting physiological damage from drought and not their increase in size or structure alone. This stress resistance would allow plants to expand into ecological niches that experience drought, eventually allowing plants to establish life on land.

“Rather than this being something that's an accident or is passive, these are really adaptations to resist this damage,” says Wilson. “All land plants are descended from algae that live in the ocean. And if you're in the ocean, you're surrounded by water. But moving onto land creates all kinds of other stresses for you, and the atmosphere is really going to dry you out. Plants have figured out quite early on various ways to evolve their internal vascular system to minimize or contain this type of damage, which allows them to grow farther out onto land.”

The project began just before the pandemic and continued through it, albeit virtually. A faculty member at Haverford for the last 11 years, Wilson has focused a considerable amount of his research on the subject of plant evolution. So when he was contacted by the other coauthors about testing this hypothesis, “I jumped at the chance to contribute,” he says.

“The overarching aim of this kind of work is to understand the forces that drive plant evolution,” says Wilson. “And in particular, what are some things that we might not quite appreciate about ways that plants respond to environmental change? Anybody who focuses on the environment, like me or my colleagues, spends a lot of time worrying about things that we don't know, or what we call non-linearities in the climate system: where a parameter changes a small amount, but you get more than that amount of change because of amplification. By studying the world around us and studying the evolutionary trajectories that got us there, I think that really gives us an appreciation for where some of these hidden non-linearities might be.

“For example, small changes in the rainfall regime or in temperature can be the difference between a plant thriving and a plant just barely surviving, or a plant just barely surviving and a plant dying. When that happens, plant mortality changes the carbon-cycle dynamics of an ecosystem, from decreased photosynthesis to increased wildfires. All these small changes can have potentially catastrophic effects as they're amplified. Trying to understand the forces that were acting on plants early in evolutionary history gives us an envelope of how plants are likely to respond in the future. I think it's important context for thinking ahead.”