Thanks to their pretty blooms and easy culture, ruellias have come into their own in recent years. Though most common in Texas, they're quickly making inroads into the rest of the South, especially among gardeners who want lots of bloom with little fuss. The flowers resemble small, thin-textured petunias. These plants resist damage by browsing deer.
R. elegans 'Ragin' Cajun'. Perennial. LS, CS, TS; USDA 8-11. The species is native from Brazil to Chile. Grows to 4 ft. tall and 8 ft. wide and is covered with scarlet flowers from late spring through frost. Needs little to moderate water after it's established. Grow as annual in Upper and Middle South (USDA 6-7).
R. humilis. WILD PETUNIA. Shrubby perennial. Native to central U.S. Grows 12 ft. tall and wide, with oval to lance-shaped leaves 14 in. long. Bears 2-in.-long bluish flowers from early summer into fall. 'Blue Shade' is a low-growing (6- to 10-in.), wide-spreading form with lavender-blue flowers; roots by creeping stems. Selection is popular in Central Texas as a ground cover for light shade.
R. macrantha. PINK WILD PETUNIA. Shrub. Zones CS, TS; USDA 9-11. Native to Brazil. To 3 ft. high and wide, with oval, dark green leaves to 6 in. long. Clusters of rose-pink, 3- to 4-in. flowers with deeper pink veining. Blooms in late fall in most areas, through winter in the Tropical South. Best grown as a container plant and given shelter during frosty weather.
R. malacosperma. MEXICAN PETUNIA. Shrubby perennial native to Mexico. Often confused with R. tweediana, but its leaves are a bit shorter and wider. Tough plant that takes dry or wet soil. Grows 3 ft. tall, 1 ft. wide, with lavender flowers in summer. 'Alba' (sometimes sold as White Flower Form) produces hundreds of pure white blooms from June through September.
R. tweediana (R. brittoniana). WILLOWLEAF MEXICAN PETUNIA. Zones LS, CS, TS; USDA 811. Shrubby perennial. Mexican native naturalized in many areas of the southern and southwestern U.S. To 3 ft. high; initially 11 ft. wide, but can be invasive and should be contained (by an edging, for example). Narrow, dark green leaves to 3 in. long, in. wide; 2-in.-long, lavender-blue flowers throughout warm times of year. 'Chi-Chi' bears soft pink blossoms. 'Katie' is a noninvasive dwarf (10- to 12-in.-tall) selection. Other dwarfs include 'Colobe Pink', pink flowers; 'Strawberries and Cream', lavender blossoms and white-speckled leaves; and 'White Katie', similar to 'Katie' but with white blooms. 'Purple Showers' is sterile and produces no seed but spreads aggressively by roots. Large, deep purple flowers form on 2- to 3-ft.-tall plants.