'Withering' can boost fertility

The secret of fertility might not be eternal youth, says a new study, which has shown that the withering action of flowers may have evolved to protect their seeds.

"No one has paid much attention to the corollas, collections of petals on a flower, when they shrivel," said Carlos Herrera, a professor of research at the Consejo Superior de Investigaciones Cientificas in Seville, Spain.

"Their job is done, so it's no surprise they die. But if their job is done, why don't the petals simply drop off the plant? I thought there might be an advantage that kept the old corollas on the plant."

To test his idea, Herrera conducted a very simple experiment. He removed dead petals from some lavender. Then he observed what happened to the seeds.

"The results for the lavender were striking," he said. "Normally you'd expect around 60% of the lavender fruits to ripen. Without the withered petals around the fruit, only 40% ripened.

"The dead petals seem to have formed a protective barrier around the fruit. In this case the barrier helps in preventing attack by gnat larvae, who like to feed on lavender seeds," Herrera said.

He also tried the same experiment with some violas but got a different result.

"For violas, I found that the petals helped to increase the number of seeds per fruit, but had no effect on ripening," Herrera said.

"It's clear that the petals are doing something important for the plant after they decay, but it is a complex relationship that needs more study. Still, it shows there is a major role for petals to play on a plant, even after the bloom of youth has gone."

The research has been published in the October 2010 issue of the Annals of Botany.