Horticulture Principles and Practices

FIGURE 3–22 Selected common
leaf margins.
Entire
Crenate
Dentate
Serrate
Lobed
Pinnatifid
FIGURE 3–23 Selected common
leaf arrangements.
(a) Alternate (b) Opposite (c) Whorl
3.4.6 LEAF MARGINS
A leaf may have an unindented margin or border or an indented one. In the latter case, there
are also degrees of expression, some being more deeply incised than others (Figure 3–22).
Some leaf margins or edges are smooth, whereas others are jagged or serrated.
3.4.7 LEAF ARRANGEMENTS
The three basic leaf arrangements are alternate, opposite, and whorl (Figure 3–23).
An alternate arrangement involves leaves set on opposite sides of the branch or stem in
a staggered pattern. In opposite arrangement, the placement of leaves is in opposite pairs;
in a whorl arrangement, leaves are placed around the stem at each node.
3.4.8 LEAF ATTACHMENT
Figure 3–24 shows a variety of leaf attachments in plants. Grasses have sheathing
(sheath) attachment to the stem of the plant, as in the case of corn, in which a tubular
structure protectively surrounds the stem. Some leaves arise directly from the plant stem
and are called sessile. Other are attached to the stem by a stalk called a petiole.
3.4.9 LEAF TIPS AND BASES
Plants exhibit a wide variety of shapes in the leaf tip and base (Figure 3–25). Tips may
be pointed or rounded. In the leaf base, certain species have an indented lamina at the
petiole-lamina junction (e.g., cordate), and others are straight (e.g., hastate).
3.4 Leaf 81