dimorphism

The existence of two distinct forms. The term may be applied to organelles (e.g. bundle sheath chloro-plasts and mesophyll chloroplasts), appendages (e.g. sun and shade leaves or juvenile and adult leaves), stages of a life cycle (gametophyte and sporophyte), individuals (e.g. males and females, i.e. sexual dimorphism), etc. See also polymorphism.