ALTERNATION OF GENERATIONS

: the occurrence of two or more forms differently produced in the life cycle of a plant or animal usually involving the regular alternation of a sexual with an asexual generation but not infrequently consisting of alternation of a dioecious generation with one or more parthenogenetic generations, the alternative forms differing greatly in appearance (as in the gametophyte and sporophyte of higher plants or the hydroid and medusa of certain coelenterates) or being distinguished with difficulty (as the dioecious and parthenogenetic females of some aphids or the sexual and asexual generations of certain algae and fungi) — compare heterogenesis , metagenesis