The seed size/number trade-off is a central topic in plant biology, reflecting ecological and evolutionary aspects of plant species. Despite theoretical and experimental evidence supporting this trade-off, it can be influenced by local variations in resource availability. We investigated the seed size number trade-off in a polyspermic perennial tree (Hymanaea stigonocarpa) at the individual plant and fruit levels. This plant species is endemic to the Brazilian semiarid, occurring on soils with low levels of water and nutrient availability. The study was conducted in the Caminho dos Gerais State Park, southeastern Brazil. Both, seed and fruit mass per plant showed a positive relationship with plant size but were not affected by seed number nor by fruit number, respectively. The absence of a trade-off mass/number of seeds and fruits is probably related to the low number of fruits produced by H. stigonocarpa: abortion of self-pollinated pistils and flowers regulates the fruit number, ensuring greater availability of resources for fruits and seeds of allogamous origin. At the fruit level, the average seed mass per fruit was not affected by the number of seeds per fruit but showed a positive relationship with fruit mass. The interaction between seed number and fruit mass indicates that fruits with lower seed number and higher mass should produce larger seeds. These results suggest the existence of asymmetric competition only between seeds that develop into small fruits. The strategy of producing large seeds at the expense of seed number by plant species adapted to harsh, fire-prone environments is discussed.