Gemellar Competition as a Key Component in Seed–Seedling Transition of Handroanthus chrysotrichus (Mart. ex A. DC.) Mattos (Bignoniaceae)

The occurrence of more than one embryo per seed (polyembryony) is common among angiosperms; however, there are gaps in the knowledge of its effects on the early stages of plant development. In this context, we study the effects of polyembryony and intraspecific variability in gemellar competition during the seed–seedling transition in Neotropical Handroanthus chrysotricus (Bignoniaceae). We used seeds from five cultivated trees in an urban environment inserted in a biodiversity hotspot (Cerrado). Embryo mass, seed germination, seedling emergence and seedling morphometry were evaluated. We did not find intraspecific variability in seed germination, seedling emergence or the mean number of embryos and seedlings per seed. On the other hand, intraspecific variability was observed during the transition from embryo to seedling. When only one seedling emerged from a seed, the seed–seedling transition was more asynchronous than when more seedlings emerged from one seed (with higher uncertainty and a longer time to emergence of the last seedling). The mass of embryos and seedlings decreased with the increase in the number of embryos in a seed, reinforcing the occurrence of gemellar competition. However, the total mass of embryos per seed was similar. The increase in seedlings per seed also decreased the morphometric measurements of each one. A positive morphometric aspect of the emergence of two seedlings per seed was that they had the highest total seedling mass, evidencing the positive Allee effect. Polyembryony had both positive and negative effects on seed germination and seedling morphology in the species, which helps to understand how this phenomenon acts on seed biology and plant establishment.