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Spring 2010

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

January 31, 2013 — UPDATE

Washington-area residents may have noticed crocuses blooming during yesterday's balmy weather. But as temperatures fell today, the flowers were still up, but not open. Here's why:

March 23, 2010

Crocuses display their thermonasty

Crocuses open their flowers as temperatures rise and close them when the mercury falls, sometimes repeating the action several times during the day. The tendency is known as thermonasty, a trait they share with tulips.

A closed flower will protect the precious pollen within from snow and rain, conserving it until warmer weather brings out more bees and other pollinators.

A temperature rise of only 0.36 degrees is enough to begin to open a crocus.

crocus mechanics

SOURCE: Journal of Experimental Botany

crocuses