I have several of these plants. This particular one, above, which I believe is one of the most common, is possibly the best of the lot.
This white one with the red centre is good, it always flowers really well.
This one tends to stay 'furled', only a few open-up completely. No idea why.
A few years ago, I admired a double white one in a friend's garden. She saved some seeds for me, but they always reverted to single. Later she gave me a plant, but that too turned out to be a single (above). We both gave up!
A surprisingly easy plant to grow. Some call them Hibiscus; I shall continue to call them Althéa.