( 2010), and Townsley and Sinha (2012) also provided relevant information. and the garden pea ( Pisum sativum L.), differ from those of the simple leaves in Arabidopsis. Developmental mechanisms of complex leaves, such as those on the tomato ( Solanum lycopersicum L.) Cardamine hirsuta L. Various details of the mechanisms that control leaf development have emerged in recent developmental and molecular genetic studies of Arabidopsis. This plant has become a model for studying eudicotyledonous, simple leaves. Genetic studies of Arabidopsis have provided a powerful tool for understanding the mechanisms of the complex processes of leaf development. Although leaf shape seems very simple, processes of development are not so simple, as demonstrated in classic studies on the ways in which division and elongation of cells occur in the leaf primordium of eudicot species ( Maksymowych 1963 Poethig and Sussex 1985). The details of leaf development remain unclear, even though there has been extensive recent progress in understanding mechanisms in the model plant Arabidopsis thaliana (L.) Henyn. Therefore, improved understanding of leaf development contributes directly to a more comprehensive concept of angiosperm biology. Moreover, leaves play important roles in photosynthesis, respiration, and photoperception. Thus, an understanding of leaf development is critical to a more general understanding of shoot development. Scales, bracts, and certain kinds of needle, such those on cacti, are also derived from leaves (see Bell 1991 Cronk 2009). The most specialized organ in angiosperms, the flower, can be considered to be a derived shoot system since floral organs, such as the sepal, petal, stamen, and carpel, are all modified leaves (see Weberling 1981 Cronk 2009). It is composed of a leaf, a stem, and a lateral bud that differentiates into a lateral shoot. The shoot system is a fundamental unit in the body plan of angiosperms and seed plants in general. Current knowledge of six important components in these developmental events is summarized in detail, followed by concluding remarks and perspectives. In the second section, I outline events in Arabidopsis leaf development, with emphasis on genetic controls. This history largely coincides with a general history of advancement in understanding of the genetic mechanisms operating during simple-leaf development in angiosperms. The first section of this review provides a brief history of studies on development in Arabidopsis leaves. Arabidopsis thaliana is a good model system for analyzing mechanisms of eudicotyledonous, simple-leaf development. Without leaves, plants would not be able to flower because all floral organs are modified leaves. Without leaves, plants would be unable perceive diverse environmental conditions, particularly those relating to light quality/quantity. Without leaves, plants cannot capture light energy or synthesize organic compounds via photosynthesis. Leaves are the most important organs for plants.

Leaf primordia