These plants are grown for their foliage, as the small lilac flowers sit deep in the leaf joints and are fairly insignificant.
There are about 35 perennial species, which are often woody at the base, but very few are found in cultivation. They originate in the Mediterranean and into Asia, and are becoming more popular as drought-tolerant plants.
They require full sun and very well-drained soil. They will also thrive in alkaline conditions.