Study Uproots Ideas on How Plants Evolved

WASHINGTON —  Scientists on Wednesday released the most complete analysis yet of how the world’s million species of plants are related to one another, overturning long-standing theories about how the first single-celled algae advanced in size and complexity to become the showy trees and flowers that stand today at the pinnacle of plant evolution.

Perhaps most surprising, the five-year effort to map the family tree for all plants--involving more than 200 scientists in 12 countries--has determined that a rare and previously unheralded tropical flower is the closest living relative of the Earth’s first flowering plant.

The unexpected discovery uproots both of the leading theories about what the first flower looked like and apparently solves what Charles Darwin called the “abominable mystery” of how plants made the leap from primitive green monotony to full floral ebullience. That global makeover fueled an explosion in biological diversity among insects and other animals as well as plants.

The new analysis, presented at the 16th International Botanical Congress in St. Louis, also comes to the jarring conclusion that there are at least three separate plant kingdoms rather than one, as most high school students are taught today.

It finds that plants invaded land not directly from the sea, as many scientists had thought, but from fresh water, where they spent millions of years preparing for the rigors of terrestrial existence.

And it concludes that the many families of green plants living on land today descended not from separate evolutionary upstarts but from a single green “Eve,” a near relative of which still lives today in pristine lakes, as it did more than a billion years ago.

The project also confirms a counterintuitive finding, first proposed six years ago, that fungi--including yeast and mushrooms--are more closely related to people than they are to plants.

“This is the first comprehensive, coordinated, large-scale attempt to reconstruct one of the major branches of life,” said Brent Mishler, a professor of integrative biology at the UC Berkeley and a spokesman for the federally funded “Deep Green” project.

Beyond the intellectual gratification that comes with understanding how the world’s plants are related, the new findings could have practical benefits, said Peter Raven, director of the Missouri Botanical Garden, which is host to the weeklong meeting of 4,000 botanists.

For example, Raven said, it makes sense for botanists seeking new medicinal compounds to focus on plants closely related to those already known to have therapeutic properties.

Conversely, conservationists worried about accelerating plant extinctions want to preserve seeds and other genetic resources from a broad array of plants. But to decide where to concentrate their efforts, they need to know which plants represent the most disparate branches of the botanical family tree.