Diana Althea or Rose of Sharon. This plant is a diploid white seedling bred by Dr. Donald Egolf at the U.S. National Arboretum in 1963. The cultivar first flowered in 1964 and was named and released in 1970. It has huge (by Althea standards) flowers of 5-6" in diameter and they are of the purest white. Its biggest claim to fame is that it doesn't set seed, so one doesn't have to worry about the seedlings coming up all over the garden. It is very drought and pollution resistant, as well as being a very heat tolerant selection. One of the best Altheas. Grow in full sun with good soil drainage.
