The genus is widely distributed along the temperate coasts of the northern Atlantic and Pacific Oceans; in the southern hemisphere it occurs along the temperate coasts of southern and eastern Africa and in the temperate seas of Australia and New Zealand. Some species penetrate to a considerable extent into tropical waters. Two subgenera can be distinguished, of which subg. Zosterella (Asch.) Ostenf. is represented by one species in Malesia. Another species of subg. Zosterella, Z. japonica Asch. & Graebn. , is widely distributedalong the eastern coast of Asia. It has been found as far south as Vietnam and Taiwan and should be looked for in the northern Philippines. It differs from Z. capricorni by the following characters: rhizome with 2 roots at each node; leaf blades always with 3 nerves; retinacula smaller, 0.5-1 mm long; seeds smooth.