Heterostyly is another mechanism to avoid inbreeding and is widely present in the family Rubiaceae. The tribes containing the largest number of heterostylous species are Spermacoceae and Psychotrieae. Heterostyly is absent in groups that have secondary pollen presentation (e.g. Vanguerieae).

Unisexual flowers also occur in Rubiaceae and most taxa that have this characteristic are dioecious.