Ruellia brittoniana 'Purple Showers'
(Mexican petunia, Common ruellia, Wild petunia)
This three-foot-tall evergreen shrub bears many tubular, blue or purple, petunia-like flowers on dark stems over a long period. Each flower lasts for just one day. It is a fast grower that may self-seed aggressively. Use in a border, container, or at waterside. Can be grown as an annual in cooler areas.