The diversity and community structure of aquatic macrophytes in aseasonal streams cool by altitude and seasonal streams cool by latitude was compared using a standardised approach. The aquatic vegetation in 12 small highland streams in the Ecuadorian Andes (3400–4100 m) and in 12 physically and chemically similar lowland streams in Denmark was examined. Our study confirmed that aquatic macrophyte communities in the neotropics are not particularly species rich. Total as well as mean species richness per stream were about the same in the two regions. The species richness within different life-forms (submerged, amphibious, semiaquatic) was, however, different as submerged plants were less diverse in the Ecuadorian streams. Further, all submerged plants found in the Ecuadorian streams belonged to cosmopolitan genera with a mainly north-temperate distribution. We suggest that the low number of submerged species in the Ecuadorian streams (four species) compared to the Danish streams (12 species) may be due to the relatively small land area and age of the high Andes, probably limiting speciation, and a low immigration of species from temperate lowlands and especially from neotropical lowlands.