Planchonella, first record of gynomonoecy for the family Sapotaceae

Documenting nonhermaphroditic sexual systems, a task of major interest for evolutionary biology, is particularly problematic in rare or remote species, for which field sampling is difficult or field specimens or herbarium material is scarce. In addition to hermaphroditism, monoecy and dioecy have been reported in the family Sapotaceae. Nevertheless, the sexual system of some New Caledonian taxa currently included in the genus Planchonella remains vaguely characterized as having "bisexual and female flowers." In the present study we investigate the significance of female flowers in Planchonella endlicheri, P. laetevirens, and P. latihila. We confirmed that P. endlicheri and P. laetevirens are gynomonoecious in nature, and that P. latihila is gynomonoecious at least when growing in a greenhouse. In addition, we found sexual dimorphism in floral size in P. endlicheri, namely a lower corolla length in female compared to bisexual flowers. Two kinds of position effects on floral sex were present in P. endlicheri. At the twig level, upper flowers had an increased probability of being female and at the inflorescence (fascicle) level, central flowers were predominantly female while lateral flowers were mainly bisexual. Our study illustrates how observational studies on rare or remote species can improve our knowledge of sexual systems in plants and document relevant evolutionary patterns in sexual dimorphism and position effects of floral sex