UMaine researcher Jay Wason helps solve century-old botanical mystery

About 400 million years ago, the earliest plants on Earth — which were only a few centimeters in length — changed their vascular systems from simple cylinders into more complex shapes, which allowed them to absorb water from soil, expand into new habitats and forever alter the Earth’s ecosystems and atmosphere. Scientists discovered this evolution 100 years ago, but one question has loomed and spurred countless debates since then: why did it happen? 

Jay Wason, a University of Maine assistant professor of forest ecosystem physiology, co-authored a Yale University-led study published in the academic journal Science that finally answered the century-old botanical mystery. 

Through extensive anatomical and microscopic analysis of living and fossilized plants, and with several simulations, Wason and his colleagues found that the earliest land plants evolved their vascular systems to better resist drought.  

When plants dry out, air-bubbles get stuck in their xylem, specialized tissue that transports water and nutrients from the soil to stems and leaves, which can kill them when left unchecked. Redeveloping their xylem into more complex shapes allowed the earliest plants to prevent drought-induced air bubbles from spreading throughout them, which, in turn, made expanding to drier habitats possible. 

“The evolution of more complex vascular systems helped set the stage for the evolution of many common plants we see today, including trees,” Wason says. “Although this research focused on early evolution of land plants, these results also shed light on how the organization of cells that transport water in wood can help trees survive drought conditions.”

Visit the Yale website to learn more. 

Contact: Marcus Wolf, 207.581.3721;