The majority of the world's flowering plants are hermaphrodite but many of them encourage cross pollination by means of spatial or temporal separation of eggs and pollen, or by genetically-controlled physiological incompatibility. A minority of species has taken the avoidance of self-pollination to its logical conclusion by evolving two distinct and sexually different forms (dioecy). In a very small number of plants, dioecy has been accompanied by the development of sex chromosomes. From the study of the development of male and female flowers of different species it is clear that there is no common underlying mechanism and that sex determination systems leading to dioecy have originated independently many times in evolution. This Botanical Briefing highlights new information from recent molecular approaches in the study of dioecy. Copyright 2000 Annals of Botany Company

Received: 14 February 2000 ; Returned for revision: 28 March 2000 . Accepted: 25 April 2000


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