Stipe growth rings in Ecklonia radiata (C.AG.) J.AG. (Laminariales)

Rings of dense tissue found in the base of the stipe of a long stiped variety of the perennial laminarian Ecklonia radiata in New Zealand result from a cycle of slow and rapid growth with periodic haptera production. These rings can be used to estimate the age of the plant. The diameter of the rings and their relationship to the medulla are affected by depth and wave exposure. The environment from which the plant was taken must therefore be known before the rings can be correctly interpreted. The number of layers of haptera gives a less precise indication of age, but haptera rot away in old plants. Ecklonia can live for at least 10 years.