Leaf Structure and Arrangement

Leaves commonly consist of at least two componets, the leaf itself, referred to as the blade, and a leaf stalk or petiole, that connects the leaf to the stalk. The angle between the stalk and the petiole is referred to as the axil and buds that develop in this area are known as axillary buds. In some plants, the petiole is absent and the leaf is attached directly to the stalk. This means of leaf attachment is called sessile. Mullein is an example of this type of plant.

Leaves can be attached to the stem of a plant in several ways. Two common ways, leaves alternating on the stem and leaves opposite each other on the stem, are shown in Figure 1. Another, somewhat less common arrangement, is for several leaves to be attached around the stem at the same level. This arrangement is referred to as whorled. See Figure 2.

Figure 1. Two Common Leaf Arrangements on the Stem

Figure 2. Leaves in a Whorl Arrangement