Photo: Anita363 (flickr)
Ajugas are perennials that are commonly known as bugles or bugle weeds, and there are about 40 species in the genus.
Ajuga reptans (reptans means creeping), is often used as a ground cover that carpets the ground with glossy rosettes of spoon-shaped leaves and spikes of violet-blue flowers in late spring.
Cultivars with variegated foliage are less vigorous than those with green or bronze leaves it seems. It is hardy zones 3-9 and prefers light shade, though it will grow in sun too.
In evenly moist well drained soil, Ajuga reptans spreads vigorously, so choose a site carefully.
Cicely Mary Barker, wrote a poem about this plant and called it, as you might guess, “The Song of the Bugle Fairy.” It appears in The Complete Book of the Flower Fairies (Penguin Books).