It certainly looks innocent enough. The modern cultivars of barberry, Berberis thunbergii, barely get taller and wider than six feet. Densely dwarf cultivars might not get much taller and wider than only two feet. Columnar sorts are quite narrow with mostly vertical stems. Even the old fashioned types get less than ten feet tall. Barberry is not exactly imposing.
However, like an angry chihuahua, it has a nasty bite. Its finely textured foliage obscures thin but very sharp spines. These spines are numerous enough to be visually appealing while the thin stems are bare through winter. Where necessary, they are sharp enough to inhibit encroachment. Unfortunately, these spines are annoying to handle while pruning.
Most popular cultivars of barberry have richly reddish or almost purplish foliage. Few are variegated with white. Some have bright yellowish chartreuse foliage. Formerly common green barberry is now rare. The small and neat leaves are obovate, and may seem to be circular. They turn vivid reddish orange through autumn, prior to defoliation during winter. Tiny red berries are rare.