Classification

In the 18th century, Carolus Linnaeus developed a system for classifying plants based on their flowering and reproduction. Taxonomists have since divided almost all trees into two groups, the gymnosperms, or conifers, and the angiosperms, or broadleaf trees. These divisions are further broken down into order, family, genus, and species.

All individuals with similar characteristics are considered a species. A collection of closely related species is called a genus. A family is composed of all the genera* that share common characteristics. Sometimes, a cultivar or variety of a species is found. These individuals exhibit minor differences in such things as needle length, for example, from others of their species. Occasionally, two species will cross-pollinate and form a hybrid. See Table 7-1, Classification of the Beech Family.

Other, common terms outside the language of taxonomic classification describe groups of trees, terms such as “deciduous,” “evergreen,” “hardwood,” and “conifer.”

Deciduous refers to trees that shed their leaves during the fall. Trees that retain their foliage year-round are evergreen. In North America, most broadleaf trees are deciduous, and most conifers evergreen. However, there are exceptions; for example, the American holly is an evergreen broadleaf and the bald cypress a deciduous conifer.

Usually, the wood of broadleaf trees is more dense, and therefore harder, than the wood of conifers. As a result, broadleafs are often known as hardwoods. Conifers are likewise referred to as softwoods. However, the wood of some broadleaf trees is quite soft—the aspen is an example—and the wood of some conifers is relatively hard—such as the southern pine.