SEXUAL SYSTEM OF EURYCOMA LONGIFOLIA JACK (SIMAROUBACEAE)

Abstract

Hermaphroditism is common in flowering plants, but the presence of unisexual flowers across many taxa, coupled with the combined influence of genetic and environmental factors, makes determining sexual systems challenging. Specifically, androdioecy, where both male and hermaphroditic individuals coexist in the same population, has often been confused with gender diphasy, a strategy in which plants alter their sex expression between seasons. In this study, we investigated the reproductive function of male and hermaphroditic flowers in Eurycoma longifolia (Simaroubaceae) to clarify its sexual system and assess whether it exhibits gender diphasy. Our findings revealed that, while male flowers were present in a notable proportion of individuals relative to hermaphrodites, they also offer significant reproductive advantage in terms of pollen contribution for siring success. Furthermore, E. longifolia displayed low self-pollination rate suggesting predominant outcrossing. The occurrences of sex changes in three individuals in the 2024 flowering season suggests that E. longifolia may not be an androdioecious species, but a possible rare example of gender diphasy.