Colonies are flat and are frequently lobed, up to 3 metres across in high latitude localities, usually smaller in the tropics. Corallites are 2-4 millimetres diameter. Paliform lobes form a neat circle around small columellae. Tentacles are sometimes extended during the day; they are short and are of two alternating sizes.
Yellow, cream, green or brown, usually pale colours in the tropics and bright colours (green or brown) in high latitude areas.
Occurs in most reef environments but especially in shaded places such as under overhangs. Also occurs on rocky foreshores of temperate locations protected from strong wave action.