Metridium senile is an anemone of very variable form. The base is wider than the column and often irregular. When expanded, the numerous tentacles form a 'plume' above a conspicuous parapet at the top of the smooth column. Large individuals may be 30 cm high. The colour is plain, commonly white orange or dark green but brown, grey or occasionally red or yellow varieties occur.Manuel (1988) describes two distinctive varieties. Var. dianthus is large with a tall column when expanded. The disc is deeply waved or folded. The many tentacles give a 'fluffy' appearance. Individuals may be 30 cm in height, with a basal diamer and tentacle span of 15 cm or more. Var. pallidus is a small form not exceeding 2.5 cm across the base with a flat disc without folds. Bucklin (1985) investigated biochemical genetic variation and concluded the presence of two morphs of Metridium senile but that they were variants resulting from different environmental conditions and were not taxonomically distinct and therefore not 'varieties' as described in many texts.