Dimorphism

Difference of form between members of the same species, as when a plant has two kinds of flowers, both hermaphrodite (as in the partridge berry), or when there are two forms of one or both sexes of the same species of butterfly.

Crystallization in two independent forms of the same chemical compound, as of calcium carbonate as calcite and aragonite.

(biology) the existence of two forms of individual within the same animal species (independent of sex differences)

(chemistry) the property of certain substances that enables them to exist in two distinct crystalline forms