Acanthus, the name of a genus of herbaceous plants native to southern Europe. There are 20 species. Acanthuses are raised as ornamental plants because of their large, deeply toothed leaves and tall spikes of white, pink, red, or lilac-colored blossoms. They are perennials but do not survive winter temperatures below 20° F. (-7° C). Some species have spiny leaves. In the United States, a widely raised acanthus is the bear's breech, which reaches a height of two feet (60 cm). It has large, hairy leaves and showy flower spikes.

The bear's breech is Acanthus mollis of the acanthus family, Acanthaceae.

In architecture, the leaves that adorn the capital (top) of the Corinthian column are copied from the soft-leaved acanthus. The acanthus-leaf design was a favorite ornamentation for the capital not only in Greek, but also in Roman, Byzantine, and Romanesque architecture. The rinceau pattern of the Renaissance, used for borders and pilasters, combined acanthus leaves with scrolls.

Acanthus plants belong to the acanthus family, Acanthaceae. They are in the genus Acanthus.