URBANITE. Crepis sancta flowers pop up along urban sidewalks in Europe, where the pressures of city living bring rapid changes in seed formation.G. Przetak

Urban living quickly drives a species of little yellow flower to make seeds that end up living with mom, say researchers in France.

A member of the dandelion family, Crepis sancta naturally produces two kinds of seeds. Most grow a miniature feather-duster that takes them wafting away on the breeze. The others, with no tuft, just fall off the mother plant to sprout nearby.

Pierre-Olivier Cheptou of CNRS in Montpellier, France, and his colleagues studied the seed strategies in the C. sancta popping up around the local sidewalk trees. There, nontufted seeds were more than twice as likely as flying siblings to land on the home patch of soil around the tree. The tufted fliers were more likely to waft beyond and risk perishing homeless on concrete.

Researchers collected seeds from sidewalk weed patches in town and from populations in large vineyards with room to soar. Grown in the same greenhouse, the plants still carried the signature of their origins. Sidewalk seedlings grew up to produce more non-flying seeds than the country cousins did. Calculations suggest urban living made the difference within 12 years, the researchers report in the March 11 Proceedings of the National Academy of Sciences.

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