A 45 million-year-old fossil flower found in northern Argentina has uncovered the evolutionary roots of Earth’s most populous plant family.
Called Asteraceae, the family includes dozens of domesticated species — from sunflowers, daisies and chrysanthemums to lettuce, artichoke and tarragon — and some 23,000 undomesticated plants. But despite its ubiquity, Asteraceae’s fossil legacy is sparse, containing little more than pollen grains. A few larger, detailed fossils exist, but they’re relatively young.
“Where the sunflower family first evolved and how it spread … is not well understood,” wrote University of Vienna evolutionary botanist Tod Stuessy in a commentary accompanying the discovery, announced September 24 in Science.
From the fossil pollen grains’ shapes and ages, scientists had previously drawn a phylogenetic tree for Asteraceae that placed its origins in a common ancestor of three existing families — itself, Goodeniaceae and Calyceraceae — that evolved in once-tropical Antarctica. As Antarctica cooled, that ancestral plant family migrated to Australia and South America. Somewhere between 56 million and 23 million years ago, the South American branch split into Calyceraceae and Asteraceae.
The new fossil flower, found by Argentina Museum of Natural History paleobiologist Viviana Barreda, resoundingly confirms that hypothetical narrative. South America is Asteraceae’s prehistoric41 nursing ground.
Meanwhile, the contemporary plant family flagged by phylogenetics as most resembling the ancestral Asteraceae, a group of Andes-dwelling plants called Barnadesiinae, indeed appear to be living fossils.
According to Barreda, the findings raise new questions even as the old are answered. Their ecological role remains unknown; so does the manner of their global spread.
Barrada wondered how these ancient Asteraceae were pollinated — perhaps, she suggested, by the first hummingbirds.
Images: 1) The early fossil Asteraceae./Science. 2) An example of Barnadesiinae, the closest living relative to the ancestral Asteraceae./Quentin Cronk, University of British Columbia.
Citations: “Eocene Patagonia Fossils of the Daisy Family.” By V. D. Barreda, L. Palazzesi, M. C. Tellería, L. Katinas, J. V. Crisci, K. Bremer, M. G. Passalia, R. Corsolini, R. Rodríguez Brizuela, F. Bechis. Science, Vol. 329 No. 5999, September 24, 2010.
“The Rise of Sunflowers.” By Tod Stuessy. Science, Vol. 329 No. 5999, September 24, 2010.
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