The term "cedar" is an example of why science uses Linnaean nomenclature instead of common names. There are trees in at least three families commonly called "cedar."
Cedar, in the original sense of the word, referred to needle-leaved trees of what science now called the genus Cedrus. There are three species of Cedrus, found in widely separated parts of the world: the Atlas cedar (Cedrus atlanticus) from Morocco; the Cedar of Lebanon (Cedrus libani) from the Middle East; and the deodar cedar (Cedrus deodara) from the Himalayas. They all share several features: aromatic wood, needles growing in tufts or clusters, and erect, oval cones somewhat like those of fir.
Other aromatic evergreen trees are also known as cedars. In the eastern US, one of the best-known of these is the eastern red-cedar, which is actually a species of juniper (Juniperus virginiana). Instead of needles, it has small, scaly leaves which cling close to the branches, and its cone is purplish and looks a bit like a berry.
The majority of trees called cedars are in the cypress family. These include northern white-cedar (Thuja occidentalis), western red-cedar (Thuja plicata), incense-cedar (Calocedrus decurrens), Atlantic white-cedar (Chamaecyparis thyoides), Alaska yellow-cedar (Chamaecyparis nootkatensis), and the Port Orford cedar (Chamaecyparis lawsonianus). These, too, have small, scale-like leaves, and cones with only a few scales. The arbor-vitaes and cypresses are of nearly identical appearance.
Finally, the Japanese cedar (Cryptomeria japonica) is in the redwood family.
The most famous use for cedar is as an aromatic wood. In the Old Testament, King Solomon hired Phoenician lumbermen to harvest cedars of Lebanon to build his temple. In more recent times, cedar chests are used for storing woolen clothes, as the aromatic wood repels the clothes moth. The same oils that make the wood aromatic also make it resistant to rot. On the Northwest Coast of North America, western red-cedar and Alaska yellow-cedar were used by indigenous nations for longhouses, dugout canoes, totem poles, and carved dishes.
Many species of cedar are also used ornamentally in the landscape. Several have been selectively propagated by horticulturists for unusual variations, such as dwarf size, weeping, globe, or columnar growth habit, and variegated foliage. Because of their strongly aromatic wood and foliage, they are less susceptible to insects than some other trees and shrubs. For this reason, sprigs of cedar can be used in drawers or other confined spaces where it is desired to keep insects away. On the other hand, the incense-cedar has its own spider-mite, Platytetranychus libocedri, specially adapted to feed on it.
Also because of the strongly aromatic quality, cedars are generally avoided by browsing animals. However, old specimens, with hollow centers, form natural "chimney-like" shelters for roosting bats and swifts, and smaller cavities hollowed out by woodpeckers can subsequently be used by squirrels, small owls, and other hole-nesting birds. Like all trees, cedar has a rich web of relationships in its natural habitat.