A remarkable dance occurs between the flowers of avocado trees every spring: they change sex daily, moving from female to male or male to female, then back before the next morning. B. Stout observed this reproductive strategy as early as 1927, but researchers couldn’t explain how it worked until now. Avocado flowers in male and female phases. Flowers at left are recently opened male-phase flowers about to shed pollen. Flowers at right are female flowers just beginning to close.