It should not be confused with genetically controlled physical or temporal mechanisms that prevent self-pollination, such as heterostyly and sequential hermaphroditism (dichogamy).
However, heterostyly is a method of actively promoting outbreeding between unrelated plants of the same species, which generates variation in the offspring -- the fuel that powers natural selection.
During the twentieth century other characters were used to delineate subfamilies, e.g. stylar pollen presentation, raphides, endosperm, heterostyly, etc.