shrub, any woody, perennial, bushy plant that branches into several stems or trunks at the base and is smaller than a tree. Shrubs are an important feature of permanent landscape planting, being used for formal decorative groups, hedges, screens, and background plantings, to which they contribute pattern, color, fragrance, or utility. In the natural style of landscape gardening they are simply allowed to grow untended, but in many gardens they are pruned in the spring or fall for greater shapeliness and to induce more compact growth. Many shrubs are beautiful even in winter because some keep their green foliage (as in the evergreen arborvitae and rhododendron), while many deciduous shrubs have decorative stem and branch forms or brightly colored fruits. Among the most frequently used shrubs in NE America are the lilac, viburnum, forsythia, azalea, flowering shadbush, cotoneaster, and barberry. In arid, arctic, and other regions of extreme climatic conditions where trees do not thrive, shrubs often provide valuable forage for wildlife and livestock as well as wood for local construction and for fuel. Tree species may grow as shrubs under unfavorable environmental conditions, and the distinction between trees and shrubs becomes one of usage rather than of strictly botanical characteristics.

Any woody plant that has several stems, none of which is dominant, and is usually less than 10 ft (3 m) tall. When much-branched and dense, it may be called a bush. Intermediate between shrubs and trees are arborescences, or treelike shrubs (10–20 ft, or 3–6 m, tall). Trees are generally defined as woody plants more than 20 ft (6 m) tall, having a dominant stem, or trunk, and a definite crown shape. These distinctions are not reliable, however; for example, under especially favourable environmental conditions, some shrubs may grow to the size of an arborescence or even a small tree.

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