Sometimes known as Chinese plumbago (and belonging to the family Plumbinaceae to which Plumbago also belongs), these are small shrubs with wiry stems that form a wide, thick clump. They flower in late summer and autumn, with very intensely blue flowers that are reminiscent of perennial Phlox. Their semi-deciduous to deciduous small leaves take on pretty tints of red and orange in autumn, which enhance the blue flowers, and in cooler areas, these will be shed in winter.
There are several species, with C. willmottianum (from West China) being the tallest (up to 1 m) and the most commonly seen. It is also the most cold-hardy species. It will reshoot even if it is frosted back to the ground over winter. C. griffithii (from the Himalayas) is lower-growing (60 cm) with a wide spread, and its leaves may take on more intense autumnal colouring. It is not so cold-hardy as C. willmottianum. C. plumbaginoides (from West China) is the lowest-growing species (30 cm) and has the largest flowers. It forms a good edging or groundcover and tends to creep about somewhat. The taller ones can be used to form low hedges. I have seen a pretty white variant of one of the species - but I am not sure which one! They grow in sun or semi-shade. Ceratostigma griffithii is possibly the most shade tolerant. The shrubs can be pruned back at the end of winter. They may self-seed, so be vigilant that these seedlings don't become a pest.