Ruellia diptercanthus is a low growing perennial shrub that produces lovely mauve to blue funnel shaped flowers that are similar to that of a Petunia - hence their common name.
These are hardy plants and although preferring warmer climates they do handle cooler nights quite well. They will even survive a light frost but they will die back as a result, only to burst back to life the following spring.
These go well in borders but also in pots, tubs and planters and attract butterflies to your garden.
N.B. They self seed easily so beware and keep contained.