The origin of leaves, no choking matter

Abstract

Why do plants have leaves? Apparently, the earliest land plants had only spine-like leaf structures. Broad leaves suddenly appeared in the fossil record ∼360 million years ago; why? Recognizing that the development of the more leafy habit coincided with a 90% decrease in atmospheric CO2, David Beerling and co-workers [Nature (2001) 410, 352–354] suggest that stomatal density is at the root of it all. As CO2 levels fall it becomes harder to drive photosynthesis, and the plants effectively choke to death. An increase in stomatal density facilitates better uptake of CO2 and, hence, the ability to photosynthesize. Development of broad leaves provides the platforms to support these increases in stomata. So plausible, it surely must be right! [Hecht, J. New Sci. (2001) 17 March, p. 6] NC