Second thoughts, it may be a wild hibiscus which would be nice.
I found this information below on this site:
PlantFiles: Detailed information on Wild Hibiscus Hibiscus pedunculatus
Hibiscus pedunculatus. A native of Southern Africa and Mozambique, this is described as a perennial herb or sub-shrub growing to 6 feet. It requires the protection of a warm house and listed as Zone 10 (minimum temp. 60f) but, in my experience will survive short periods of temperatures down to 45f. The flowers are solitary, pale rose-purple to pale lilac in colour (see picture), and can grow to nearly 3” across. Easy to raise from seed or cuttings sown under glass in Spring.
Also, see this link
http://davesgarden.com/guides/pf/b/M...ne/cultivar/0/. It has loads of photos of wild hibiscus and several of them look exactly like yours.