Trees are all around most of us. They grow in the wild and are cultivated in yards, parks, and even along the median of streets to provide shade and beauty. However, for all that familiarity, it can be somewhat difficult to define what makes a tree different from a shrub or other woody perennials.

Trees are generally at least 13 feet tall, have a trunk of at least three inches in diameter, and a defined crown. Shrubs, on the other hand, are woody plants that usually grow close to the ground and do not grow beyond 13 feet in height. They have multiple stems, rather than a single trunk, and no defined crown. Of course, there are many species of true trees that can be trained not to grow beyond a certain height and are kept small for ornamental purposes. This is considered the art of bonsai.

Trees can be evergreen (keep their leaves through the winter) or deciduous (lose their leaves in the winter). Most bear some sort of fruit, although many types are inedible or rarely used as food today. For instance, acorns were once a stable food, but are not eaten by many people in the developed world today. All trees reproduce with seeds, and most trees encase those seeds in some sort of fruit. Note that nuts are technically dry fruits.

The bulk of most trees is the trunk, which actually consists mostly of dead material. The only living tissue on a tree’s trunk is a thin layer just under the bark. The interior of the trunk consists of hard, dead tissue that supports the tree’s vertical growth.