Angling for more Light

Courtesy of Pau Atela, Smith College

Most flowering plants arrange their leaves and petals in spirals around their stems. And in most species, the angle between successive elements is close to the so-called golden angle, 137.5 degrees, a number derived from mathematic theory that correlates to artistic aesthetics and biological patterning. This convergence has puzzled researchers for 250 years.

A German team now suggests that the arrangement minimizes the shadow each leaf casts on those below it, maximizing the plant's light-gathering ability.¹ Physicist Friedrich Beck and colleagues at Darmstadt University of Technology built an optimality model of light capture and found that the angle between leaves tended towards 137.5 degrees as leaves became thinner.

The model's predictions matched results from an earlier study on geometry and light-capture efficiency of the forest-dwelling daisy Adenocaulon bicolor. "The model reproduced the experiments in an astonishing way," says Beck. "It gave...