Natural variation in leaf growth and development in several Arabidopsis accessions collected from distinct geographical locations. Natural variation is often observed as a phenotypic continuum, as opposed to presence or absence of the trait. Here, for example, all accessions have leaves, but the size, shape, and number is variable. The molecular mechanisms regulating quantitative traits such as leaf size and shape can often be applied to improve crop science and plant breeding programs. Figure from the website of Dr. Matthieu Reymond, Max Planck Institute for Plant Breeding Research, used with permission of Dr. Martin Koornneef.