Go Home

 

Summary of Basic Forestry Concepts Helpful in Tree Identification

 

    It is easier to distinguish between trees when you know some basic leaf, flower, and fruit characteristics. When looking at leaves, one of the first things to notice is if the leaf is simple or compound. A simple leaf comes directly off the twig at the node. It consists of a leaf blade and leaf stalk. A compound leaf does not branch out singly from the node like a simple leaf. Rather, it has multiple blades coming from a central stalk, the axis. It is thus incorrect to call the blades of a compound leaf “leaves.” Instead, the whole leafy stalk from the node to the end blade is called the leaf. A compound leaf can be arranged in either a pinnate or palmate shape. If the leaf is pinnately compound, the blades will come off the axis opposite from one another. There is often a single end blade. A palmately compound leaf will have a cluster of blades at the end of an axis.

    Another important distinction is whether the leaf arrangement is opposite or alternate. Oppositely arranged leaves come off the twig directly across from each other, with two leaves per node. Compound leaves are usually arranged like this, with one axis extending opposite from the other across a twig. Alternate leaves are arranged with one leaf per node, and are not directly across from one another.

    The leaves of different species have predictable shapes, although the shapes of individual leaves on a tree may vary depending on sun exposure, maturity, etc. Some trees even have varying leaf shape as one of their key characteristics (such as Sassafras). However, most trees have one of a number of leaf shapes. These include elliptical, lanceolate, oblanceolate, ovate, obovate, oblong, linear, truncate (square), and heart-shaped. These shapes are modified by the apex, base, and leaf edges. The base or apex may be rounded, pointed, square, lobed, oblique (uneven), or pointed with a long or short point. The edges of the leaf can be entire (smooth and without teeth), lobed, or toothed. A lobed leaf is indented along the edges with lobes that stick out and sinuses that dip in. The degree of lobing will vary from shallowly lobed to deeply lobed depending on species. If toothed, they can be coarsely, finely, or doubly (smaller teeth on each big tooth) toothed. The teeth can also be wavy, rounded, curved, or randomly spaced.

          The leaves also have a characteristic venation, the way the leaves’ veins branch. A leaf is either pinnately or palmately veined. A pinnately veined leaf has one main central vein, the midvein, from which side veins branch. A palmately veined leaf does not have a midvein; it has multiple veins that run from the leaf’s base to the edges. Along with all of these characteristics, leaves’ color, texture (hairy/leathery/smooth), thickness, and size are also important. Evergreen leaves, which remain attached throughout the winter, are usually thicker and more leathery than deciduous leaves, which do not remain attached through winter.

            Flowers and fruits are also important although there is not much emphasis on them in the tournaments. A flowering species can be either monecious (“1 house”) or dioecious (“2 houses”). Monecious species have both sexes (male and female) on a single tree, although each flower may not have both male and female parts. If each flower only has one set of parts, the flowers are termed “unisexual.” If each flower has both male and female parts, the flowers are “bisexual.” So, a tree can be monecious and be either unisexual or bisexual. However, a dioecious tree, which has the sexes on separate trees, can only be bisexual, with only male/female parts in each flower and these on separate trees.

            Flowers have distinct shapes, and can be single or in clusters. The various shapes of flowers are on their Illustrations page. A common shape is a drooping or upright catkin of flowers, where the largest flowers are at the base and smallest at the end. A flower is composed of numerous parts, starting with the calyx as its outermost part. The calyx is the collective term for all of the sepals, the leaf-like parts at the base of a flower.  Inside the calyx is the corolla, the term for all of the petals. Some species’ flowers lack a calyx or a corolla. Inside the whorls of the calyx and corolla are the reproductive parts of a flower. If the flower has both male and female parts (so it is unisexual), the male parts will usually circle the female parts. The male parts are the stamens, which are stalks tipped with pollen. The stamen’s stalk is called a filament while its tip is the anther. In the center of the stamens should be a pistil, the female part. The pistil, too, has a stalk, the style, and a tip, the stigma. Then, inside the base of the pistil is the ovary. The ovary is the compartment that encases the ovules, which will become seeds when fertilized. The ovary around the seeds will become the fruit.

    Fruits can be simple, compound, or an aggregate. Aggregate and multiple fruits are clusters of several fruits. Each simple fruit is a single fruit that develops from a single ovary in a single flower. Each aggregate fruit also develops from a single flower, but from multiple ovaries within that flower. A multiple fruit, though, comes from multiple flowers. Another distinction between fruits is whether they are fleshy or dry. Fleshy fruits include berries (with more than 1 seed), pomes (with a papery inner wall), and drupes (with a stony core).  Dry fruits can be dehiscent (splitting when they fall) or indehiscent (not splitting when they fall). Some dry fruits are achenes (small; indehiscent), capsules (multiple seeds; dehiscent), pods (thicker than capsule; dehiscent), follicles (dehiscent), cones (with scales), keys (also known as samaras, 1-seeded), and nuts (acorns are indehiscent nuts).

   Although many of these terms and distinctions are not necessary for distinguishing between tree species, they are helpful and good for Forestry Science Olympians to know. You might notice that these terms (which are also defined on the Vocabulary page), are different from those commonly used in Botany. I have tried to use the same set of vocabulary that Audubon uses.