Seed dormancy is considered an adaptive strategy in seasonal and/or unpredictable environments because it prevents germination during climatically favourable periods that are too short for seedling establishment. Tropical dry forests are seasonal environments where seed dormancy may play an important role in plant resilience and resistance to changing precipitation patterns. We studied the germination behaviour of seeds from six populations of the Neotropical vine Dalechampia scandens (Euphorbiaceae) originating from environments of contrasting rainfall seasonality. Seeds produced by second greenhouse-generation plants were measured and exposed to a favourable wet environment at different time intervals after capsule dehiscence and dispersal. We recorded the success and the timing of germination. All populations produced at least some dormant seeds, but seeds of populations originating from more seasonal environments required longer periods of after-ripening before germinating. Within populations, larger seeds tended to require longer after-ripening periods than did smaller seeds. These results indicate among-population genetic differences in germination behaviour and suggest that these populations are adapted to local environmental conditions. They also suggest a role of seed size in germination timing within populations. Ongoing changes in seasonality patterns in tropical dry forests may impose strong selection on these traits.