4 - Leaf

Summary

Leaves are determinate lateral organs that are usually dorsiventrally flattened and lack a growing tip. Foliage leaves are green; they are typically borne on stems above ground level because they require sunlight for photosynthesis. Angiosperm leaves consist of a sheathing leaf base that clasps the stem at the node and a distal zone that extends away from the stem to capture light effectively. In eudicots and magnoliids, the sheathing lower zone is often reduced or sometimes absent and the distal zone forms the bulk of the leaf, consisting of a petiole and an elliptical blade (lamina) with net-like (reticulate) venation (Figure 4.1). The margins of the lamina can be smooth, lobed or toothed.