Wheat is an example of a plant that needs exposure to cold weather in the winter before flowering in the spring. (Credit: http://www.flickr.com/photos/meganpru/207519162/)

Warmer temperatures have caused some flowers to bloom earlier — but the response isn’t universal. Several species have confounded scientists by showing their colors later in warmer spring weather.

One possible explanation: Flowers that bloom later than expected are remembering warm winter weather, according to research presented Thursday afternoon at the American Geophysical Union’s Fall Meeting.

Scientists who study the timing of plant development have speculated that some plants may not respond to climate change because they use other cues­—like day length—for flowering. Other plants need cold winter weather to flower or sprout from seed. The adaptation—called vernalization—keeps the plants from reproducing in the autumn when they need to wait until spring to sprout.

“People have looked at this vernalization response in the lab, but people haven’t tried to look at it using long-term trend observations,” said Benjamin Cook from the NASA Goddard Institute for Space Studies in Maryland.

Cook and his colleagues used a unique, long-term ecological dataset in their study. A father and son had collected flowering times from 384 species in the United Kingdom between 1954 and 2000.

“We could only really do this with this data set,” Cook said during a poster session on plant life-cycle responses to climate.

Of the species in the dataset, 70 did not bloom earlier with a warmer spring. The researchers used a statistical model and found that including fall and winter warming, along with spring warming, explained the behavior of those species.

Plants that needed cold weather to get started were still responding to climate, said Cook. But spring and winter warming effects were pulling the plants in opposite directions. Spring warming makes them flower earlier, but thanks to their survival adaptation, winter warming makes them late out of the gate.

-Sarah Keller is a science communication graduate student at UC Santa Cruz