A North American genus consisting of mostly drought and heat tolerant clumping perennials or sub-shrubs with tubular flowers. There are many spectacular species and cultivars in a wide range of colours from white through pink, red, purple and a few yellows but most notably blues of a luminosity rarely found in other genera.

Wild species tend to be more heat and drought tolerant than English hybrids developed for milder climates, though all demand ample sunlight and excellent drainage, preferably with poor soil.