TREE IDENTIFICATION

TREE IDENTIFICATION:

There are many characters used to identify trees, and it is important that you become acquainted with the following three: leaf, fruit, and silhouette.

Leaf

Leaves are the primary photosynthetic organs of most plants. Although they are often the most variable part, they are an important means of discriminating among species because of their many distinctive features, and their convenience. Leaves are formed on stems at regular intervals, and the point on the stem at which one or more leaves arise is called a node. The portion of the stem between the nodes is the internode. The expanded portion of the leaf is the blade, and the supporting stalk is the petiole.

There are two fundamental types of leaves. A simple leaf has only a single blade and is joined by its petiole to a woody twig. A compound leaf is divided into three to several dozen leaflets. The leaflet of a compound leaf is attached by its petiole to the rachis, which is attached to the twig. Whether simple or compound, leaves are usually arranged in one of three ways: opposite, when they are paired at the same node, one on each side of the twig; whorled, when more than two are found at the same node; and alternate, when only on leaf is attached at each node and leaves are arranged in spirals around the twig. Types and arrangements of leaves are shown in Figure 1. In addition to leaf type and arrangement, taxonomists use features like leaf size, shape, color, texture, and venation to identify and classify trees.

Fruit

A seed is a ripened ovule, usually with an embryo. The seed-bearing structure of the plant, termed fruit in angiosperms and cones in conifers, are extremely important in identifying tree species. Fruits and cones are more accessible than flowers because they stay on the tree for a longer time. Some fruits may persist even after the leaves have fallen.

If the fruit develops from a single ovary in a flower, it is a simple fruit. Simple fruits can be fleshy like the pome, berry, drupe, and hesperidium, or they can be dry like the achene, samara, nut, legume, follicle, and capsule. If the fruit develops from several separate ovaries that stay together when matured, it is a compound fruit. Compound fruits are termed either aggregate if they develop from a single flower with many pistils or multiple fruits if they developed from many flowers. Figure 2 shows examples of simple and compound fruits.

Silhouettes

Recognizing a tree’s overall silhouette is often a means to identification because many trees have a characteristic shape. Caution must be taken, however, because trees can assume a variety of shapes. A young tree might look entirely unlike a grizzled veteran of the same species. A forest grown tree reaching for the light, might grow tall, slender, and restricted in its branching, compared to a field grown tree where plenty of sun, soil, and moisture have enabled it to develop a maximum crown. With practice one can recognize the general shape and branching pattern of quite a few trees. Figure 3 provides some examples of silhouettes of trees you can find on campus.