Dimorphism

Part of speech: noun (n.)

1. 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. Dimorphism is the condition of the appearance of the same species under two dissimilar forms. Darwin.

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