Evolutionary History of Flowering Plants Reveal They May Not Adapt Quickly to Climate Change

Human-induced climate change may be more deadly than we thought--at least when it comes to plants. Scientists have used the largest dated evolutionary tree of flowering plants ever assembled to show that some plants may not adapt quickly to future changing temperatures.

Early flowering plants, known as angiosperms, are thought to have been woody. This means they maintained a prominent stem above ground across years and changing weather conditions, such as a maple tree. In addition, they were restricted to warm, wet, tropical environments. Since then, though, they have put down roots in colder climates and have dominated large swaths of the globe where freezing occurs. How they managed this expansion, though, has long vexed researchers.

"Until now, we haven't had a compelling narrative about how leaf and stem traits have evolved to tolerate cold temperatures," said Amy Zanne, one of the researchers, in a news release. "Our research gives us this insight, showing us the 'whens,' 'hows' and 'whys' behind plant species' trait evolution and movements around the globe."

In order to identify evolutionary adaptations to problems like freezing and likely paths, the researchers built two sets of data. They first created a database of 49,064 species, recording whether each maintains a stem aboveground over time, loses or keeps its leaves, has been exposed to freezing and the width of its water-carrying pathways. The scientists combined the information with a dated evolutionary tree of 32,223 plant species and modeled the evolution of species' traits and climate over time. This identified the order of evolutionary events.

Using this "timetree," the researchers then identified three repeated evolutionary shifts they believe flowering plants made to fight the cold. The plants either dropped their leaves seasonally, developed thinner water-conducting pathways or avoided cold seasons altogether by losing aboveground stems and leaves and retreating as seeds, or stored organs underground, such as tulips or potatoes.

That's not all the researchers found, either. They also discovered that woody plants most often became herbs or developed thinner pathways before moving into freezing climates. Plants that dropped their leaves also usually did so after moving into freezing climates. Yet these changes did not occur rapidly.

"Some of these changes were probably not as simple as we once thought," said Pam Soltis, one of the researchers, in a news release. "Adjusting to big shifts in their environments is probably not easy for plants to do."

The findings reveal that while plant adaptations were extensive and important, they also did not occur quickly. This means that the relatively rapid and current climate change could drastically impact plants.

"The onset of freezing temperatures did not affect the entire world, but only certain habitats became colder," said Soltis in a news release. "Certain lineages could not move into the cold, but were able to persist unaffected by the cold in warmer areas. With climate change that is human-induced, all habitats will be affected over a short period of time, and plants and other organisms will have to adapt quickly if they are to survive."

The findings are published in the journal Nature.