Sexually dimorphic breeding systems—dioecy and gynodioecy—provide a window into the ecological and evolutionary processes shaping plant diversity, yet their global distribution remains elusive. Using a dataset of 369,604 angiosperm and 1,492 gymnosperm species, we reveal contrasting geographic patterns. Gynodioecy peaks at higher latitudes and declines toward the equator, while dioecy shows the opposite trend, increasing in tropical regions. These gradients persist across growth forms and are shaped by distinct climatic drivers: gynodioecy declines with increasing growing season temperature, while dioecy becomes more common with warmer winter minimum temperatures. Gynodioecious species occupy broader geographic ranges, especially among herbaceous taxa, whereas dioecious species tend to have narrower ranges and are disproportionately represented on islands, independent of insular woodiness. Our findings provide the most comprehensive global analysis of sexually dimorphic breeding systems to date, offering insights into how reproductive strategies, growth form, and climate collectively shape global patterns of plant diversity.