They can get huge. I've seen some that were a couple feet across. Being stressed in some way will also encourage them to split as a means of increasing their chances of survival. My LTA would split 3:1 every time we moved the tank. I was overrun with them at one time because we were moving so often. The really large ones will just clone off small anemones occasionally.

I had a RBTA climb and straddle the grates in an overflow once. It was basically impaled and the only way I could get it off was to split it with a razor blade. I got two nice, small RBTA as a result.

Try checking this out:

http://www.wetwebmedia.com/marine/in...ereprofaqs.htm