In the Caribbean slope of Isthmian Central America, plant associations dominated by the palms Raphia taedigera and Manicaria saccifera develop in poorly drained or waterlogged soils. These associations are known locally as yolillales or palm-swamps, although there are differences in the forest structure and plant diversity associated with both palm species. In this paper, we report the results of a preliminary inventory of tree species found in eight palm-swamps at five locations in southeastern Nicaragua and northeastern Costa Rica. Our data reveal low tree diversity in these swamps with only 60 species accounted in them. This figure is equivalent to close to 8% of the plant species known for this region. In general, R. taedigera dominates flooded areas with extensive hydroperiods and lower floristic diversity, while M. saccifera is often found in flooded forests with more structure and diversity.