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Trees and shrubs

• How their parts are described
• Leaves
• Leaf & Lateral Bud Arrangement
• Kinds of Shoots
• Shoot-tip Abortion and Pseudoterminal Buds
• Flowers, Flower Clusters, & Fruits
• Pollen Cones & Seed Cones
• Bark & Wood

This is a field guide about trees and shrubs. Trees are long-lived (perennial), tall, woody plants that have a single stem (trunk, bole, or mainstem) that carries a crown high above the ground. The stem is anchored in the ground by an extensive, below-ground root system, which also provides the tree with water and nutrients. A shrub, similarly, is a woody, perennial plant that has a crown and root system, but between these two parts there are several stems that arise near the base, and the whole plant is relatively short in stature.

In both trees and shrubs, the crown is made up of branches which bear side branches, or branchlets, which, in turn bear twigs or shoots. In fact, the whole above-ground part of a tree or shrub is produced by a succession of shoots that, with increasing age and thickening, become the twigs, branchlets, branches, and stems.

Each year, the crown extends by producing shoots. It is only on these new shoots that new leaves are produced. The leaves enable the plant to produce the food materials that it requires for its continued existence and growth. Some of the shoots produce reproductive structures (flowers, inflorescences, and fruits with seeds, or pollen cones, seed cones, and seeds).

Shoots may extend in one of three ways: (1) entirely from a miniature preformed state from inside an overwintered (dormant) scaly bud; (2) from a miniature preformed segment from a bud, followed by extension of a neoformed segment; or (3) entirely by neoformed extension. Neoformed extension is when the shoot parts (the leaves and their stem internodes) are newly initiated and extend directly to maturity without undergoing a period of dormancy and, therefore, without involvement of a scaly bud. Sometimes the features of preformed and neoformed structures on the same plant are different (as, for example, are the preformed and neoformed leaves produced by a long shoot of the sugar maple tree).

As a shoot ages through the growing season, its axis becomes woody, its surface features or color may change, buds may form in certain locations along its length, and its leaves may die and fall off, leaving scars where they were attached. At such a stage, the shoot is generally called a twig.

Features of leaves, shoots, twigs, buds, leaf scars, flowers, inflorescences (flower clusters), fruits, pollen cones, seed cones, seeds, and bark are useful for identifying species. Description of these items constitutes the morphology of the species. Coupled with morphology, the general form of the whole plant and the kind of habitat in which it usually grows aid in species recognition.

Nomenclature refers to the scientific names given to plants. Botanists mostly use the fine features of flowers or cones to classify species into genera, and genera into families. The scientific names given to plants reflect the genus (the first part of the name) to which the species (the second part of the name) belongs. These two parts of the name are in Latin, and are italicized in type. The last part of the name, which need only be stated at the first mention of the species in a piece of writing, is the name (often abbreviated in standard form) of the person or sometimes group of people who first named and described the particular plant. Thus, Acer saccharum Marsh. is the species called saccharum (meaning sweet or sugary) by Marsh. (Humphrey Marshall, an American botanist and dendrologist), who placed it in the genus called Acer. The value of scientific names is that they are exact and universal, and their usage is governed by an International Code of Botanical Nomenclature. In contrast, common or vernacular names can be confusing. For example, in this guide, Acer saccharum is given the common name “sugar maple”, but the same species is sometimes called hard maple, rock maple, or érable à sucre.

The fine features of flowers or cones may be observed only in certain years and then only at certain times of the year and, of course, only on plants developed enough to carry them—and often, they are carried near the tree tops! Thus, they are thus relatively poor features for practical field identification, though some of their more easily discerned characteristics are included here.

The principal ways in which the species’ features are described in this work are given in the following sections.