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Chemical Clues to Darwin's Abominable Mystery

From the peony, with its showy blooms, to the modestly endowed daisy, all flowering plants share a common ancestor. But exactly how and when this group originated has long puzzled scientists. The earliest known flowering plant fossils date to around 130 million years ago, yet transitional fossils linking them to other ancient plants are unknown. Indeed, Charles Darwin himself dubbed the sudden appearance of the flowering plants in the fossil record "an abominable mystery." Now new research, described yesterday at the annual meeting of the American Chemical Society, suggests that these flora evolved more than 120 million years prior to the appearance of their earliest known fossil representatives.

Stanford University geochemist J. Michael Moldowan and his colleagues studied a compound known as oleanane, which is produced by many flowering plants as a defense against insects and microbial invaders. It is not, however, found in other seed plants such as pines and gingkoes. The team was able to retrieve oleanane molecules from oily rock deposits dating back to the Permian period, hundreds of millions of years ago. Specifically, they found the compound in sediments containing extinct plants called gigantopterids, making these the oldest known oleanane-producing seed plants. As such, they were probably among the earliest relatives of the flowering plants, team member David Winshop Taylor of Indiana University Southeast concludes.

Taylor adds that their findings hold even more significance in light of another recent discovery¿ancient gigantopterid fossils from China exhibiting leaves and stems similar to those of modern flowering plants.

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