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The Oldest Flower

ST. LOUIS, MISSOURI--Pamela Soltis calls it botany's answer to the human genome project: a 5-year effort to compile data on the genes and traits of green plants into a vast family tree spanning the millennia, from an unknown freshwater ancestor to the impatiens and petunias that line sidewalks today. Preliminary results from the biggest project on the phylogeny, or evolutionary history, of organisms ever conducted, discussed here today at the 16th International Botanical Congress, pinpoint the most primitive flowering plant.

Launched in 1994, the Green Plant Phylogeny Research Coordination Group involves 200 scientists from 12 countries. One of its earliest fruits is setting the record straight on the oldest existing angiosperm, or flowering plant. Some scientists had pinned magnolias or water lilies as the most primitive angiosperms. But the new findings suggest that amborella, a tiny plant with pale yellow flowers and red fruit found only in New Caledonia, arrived earlier, diverging from an extinct ancestor over 100 million years ago.

To bequeath that honor on amborella, Soltis and her husband Douglas Soltis, botanists at Washington State University in Pullman, along with Mark Chase of the Royal Botanic Gardens in Kew, England, analyzed differences in three DNA sequences--from the plastid genes rbcL and atpB, and nuclear 18S rDNA--in 560 angiosperm species. They concluded that amborella has the most primitive DNA sequence. Three other genetic studies presented at the meeting concur. "The degree of correlation among these findings is a real rarity," says Christopher Haufler of the University of Kansas, Lawrence. "It gives us a point of origin for the angiosperms."

By the time it's completed, the phylogeny project should give biologists an evolutionary guide to all green plants that could yield insights into as-yet-undiscovered species. "When you want to learn about an unknown organism, phylogeny is the single best predictive tool you've got," says Brent Mishler, a University of California, Berkeley, biologist and one of the project leaders. "Now we've got a new map to show the way."