Verbena pulchella ssp. gracilior
If you're looking for a very
prostrate ground cover this might meet your needs. Compared to other
verbenas, Rock verbena has very delicate, lacy foliage, and a flat
growth habit, to about 8 inches tall by 4 feet wide. Its flowers are a
more subtle shade of purple than those of Sandpaper verbena. Like Verbena
gooddingii, Rock verbena can be short-lived, but naturalizes
in the landscape. It is hardy to 20° F. USDA Zone 9.