Leaf development and evolution.

The number of publications on "leaf morphogenesis" has increased annually since the early 1990s, when the Arabidopsis 'model plant' concept began being applied to studies of mechanisms of leaf morphogenesis. Nearly 20 years have passed since then, and a great leap in the understanding of leaf organogenesis has been made. As a result, so-called evo/devo studies on leaf development have joined the trend in leaf morphogenesis/development studies in the latter part of the present decade. This article is a brief overview of the progress made in the research to date and an introduction to the articles that appear in this special issue.