2.6 Leaves

There are so many Types Here are some hints that sometimes can

help you decide whether the thing you're seeing is a leaf:

Leaves of most woody trees and bushes consist of a flat blade connected to the woody stem or twig via a slender, stick-like petiole. The blade and the petiole make up the leaf.

On most woody trees and bushes, inside the narrow angle formed where the petiole connects with the stem, there arise one or more buds. Buds contain embryonic leaves, stems, or flowers, depending on the buds' type.

Blade

Petiole

Bud

Finding buds is especially helpful if you're confronted with leaves divided into subdivisions, or leaflets. Such leaves are called compound leaves, while undivided leaves are known as simple leaves. Hundreds, even thousands, of leaflets can occur in a single compound leaf.

Can you find or see the bud on the compound leaf?

Most but not all leaves, even compound leaves, are shaped in such a way that they more or less display bilateral symmetry. The three leaves above show this, each leaf's pink side more or less being a mirror image of its other side.

Finally, don't forget that some plants just don't have "standard leaves.“

Another variation on the leaf theme is presented by the pines, where needles serve the leaf function.

Even simple leaves can have lots of interesting ways of being. The above leaves, also picked up right around my home, show a variety of leaf margins.

Leaf-margin A is the crenate margin of the Swamp Cottonwood tree, Populus heterophylla.

Leaf-margin B is the spiny-toothed margin of the American Holly, Ilex opaca.

Leaf-margin C is the entire margin of a Greenbriar, Smilax sp.

Leaf-margin D is the shallowly lobed margin of an immature leaf of the Black Oak, Quercus velutina.

Leaf-margin E is the dentate margin of a wild grapevine, Vitis sp.

Leaf-margin F is the doubly toothed or twice serrated margin of the Eastern Hophornbeam, Ostrya virginiana.

Another identifying feature is to notice whether on the stems or twigs one leaf arises at each node, or two, or more. If only one leaf arises, then the leaf is alternate. If two, then opposite. Three or more leaves at a node are said to be whorled.

A plant living for only one year is called an annual.

A plant living for more than three years is called a perennial.