All of the 'host' anemones we keep are capable of both sexual and asexual reproduction--just some methods are used more than others in certain species. No, there is no external way to tell. There are two ways to tell: a) let it spawn or b) dissect it, finding corresponding sex organs. Since most do not opt for the latter (nor should you really do it in most circumstances), allowing the anemone to spawn is the only 'good' way to tell. Males will excrete cloud-like sperm, whereas females will excrete copious amounts of greenish eggs, approx. 1-2 mm in diameter in slimy 'pouches.'