A dense, mounding, rounded deciduous shrub from Japan, 3-6 feet tall and 4-7 feet wide, with arching thorny stems, small spoon-shaped leaves (green, or burgundy and gold in cultivars), pale yellow spring flowers, and bright red berries that hang into winter. It is tough, deer-resistant, and tolerant of shade, drought, and poor soil. That toughness is exactly the problem: Berberis thunbergii is an aggressive invasive across the eastern and midwestern United States — birds spread its seed into woodlands, where dense thorny thickets crowd out native plants. Its stands are documented to raise ground-level humidity and to harbor markedly higher densities of blacklegged (deer) ticks, the vector of Lyme disease. It is banned or restricted for sale in several states, and native or non-invasive shrubs are the better choice almost everywhere it is hardy.