There is something particular about plants that arrive by accident and prove better than anything that could have been planned. 'Purple Smoke' emerged as a chance seedling at the North Carolina Botanical Garden in the early 1990s, the offspring of Baptisia australis and B. alba, and it earned its place by being unmistakably itself. In mid-spring, long racemes of smoky lavender flowers rise on dark stems — straight or gently arching — above gray-green foliage that holds its color and composure through the entire growing season. The combination is atmospheric in a way that earns the name.

This is a large false indigo: 4 to 5 feet tall and equally wide, so give it room and a permanent address, because the deep taproot makes transplanting impractical. In full sun and average well-drained soil it is tough, deer-resistant, and drought-tolerant once established. Prune after flowering to keep the mound tidy; leave it alone and elongated seed pods will extend the interest into fall. Hardy in zones 4 through 9, it works best as a specimen or at the back of a mixed border where its scale and form anchor the planting for decades.