Aiming to analyze the pollen tube growth behavior in compatible and incompatible crosses in Poincianella pyramidalis, on-field crosses were performed using flowers of 30 randomly selected individuals, which were self- and cross-pollinated. In the cross-pollination, the pollen germinated and the pollen tube grew in the transmitting tissue of the pistil, followed by a succession of callose rings through the growth of the tubes towards the ovary; after 8 h, the ovules were fertilized. On the other hand, in self-pollination, the pollen grains germinated, but the pollen tubes were inhibited during growth at the stylar transmitting tissue, indicating that the self-incompatibility of the species is homomorphic and gametophytic. Key words: Fabaceae, self-incompatibility, Caatinga, Poincianella pyramidalis, incompatible crosses, compatible crosses.