Aim: The aim of this study was to evaluate the richness and distribution of the aquatic macrophytes in the basin of the Apodi/Mossoró River, in the semi-arid region (caatinga) of Rio Grande do Norte, Brazil; Methods: A survey of the floristic composition of the aquatic macrophytes was made at 20 sampling stations in the basin at four seasons (August/2007, November/2007, February/2008, May/2008. Specimens of each species were collected and deposited in the Dárdano de Andrade Lima Herbarium of the Universidade Federal Rural do Semi-Árido; Results: We found 40 species of aquatic macrophytes, in 33 genera and 22 families. The families with the most species were Poaceae and Cyperaceae, and the most species-rich genera were Cyperus and Eleocharis. The most common plant form was amphibian (42.5%), followed by emergent (27.5%), free-floating (12.5%), rooted-submersed (10.0%), and floating-leaved (7.5%). The lowest richness was observed at the estuarine region (3 species), and the highest richness in the upper basin (17 species). The rooted-submersed Hydrothrix gardneri Hooker f. and Ceratophyllum demersum L. were observed in great abundance and frequency in the Santa Cruz Reservoir of Apodi, especially in areas close to cage farms of Nile tilapia (Oreochromis niloticus) (Linnaeus, 1758). The most common free-floating species were Eichhornia crassipes (Mart.) Solms., Pistia stratiotes L., and Salvinia auriculata Aubl., predominantly in stretches that run through urban centers; Conclusion: The species richness of aquatic macrophytes in aquatic environments of the caatinga is similar to that observed in other basins of Brazil. Because of the many dams and reservoirs in the semi-arid Northeast, inventory and monitoring of aquatic macrophytes have become essential, especially in basins that will receive water from the diversion of the São Francisco River.Keywords: aquatic plants, floristic inventory, basin, water diversion, caatinga.Resumo: Objetivo: Nós objetivamos avaliar a riqueza e a distribuição das macrófitas aquáticas nos ambientes aquáticos da bacia hidrográfica do Rio Apodi/Mossoró, no semi-árido do Rio Grande do Norte; Métodos: A investigação da composição florística das macrófitas aquáticas presentes em 20 estações de amostragem da bacia hidrográfica, em quatro épocas do ano (Agosto/2007, Novembro/2007, Fevereiro/2008, Maio/2008. As espécies foram coletadas e depositadas no herbário Dárdano de Andrade Lima da Universidade Federal Rural do Semi-Árido; Resultados: Foram identificadas 40 espécies de macrófitas aquáticas distribuídas em 33 gêneros e 22 famílias. As famílias com o maior número de espécies foram Poaceae e Cyperaceae e os gêneros mais representativos foram Cyperus e Eleocharis. A forma biológica mais freqüente foi a anfíbia (42,5%), seguida pelas emergentes (27,5%); folhas flutuantes (12,5%); submersas enraizadas (10,0%) e com folhas flutuantes (7,5%). A menor riqueza foi observada na região estuarina (três espécies), e a maior riqueza na parte alta da bacia hidrográfica (dezessete espécies). A...

Aim: The aim of this study was to evaluate the richness and distribution of the aquatic macrophytes in the basin of the Apodi/Mossoró River, in the semi-arid region (caatinga) of Rio Grande do Norte, Brazil; Methods: A survey of the floristic composition of the aquatic macrophytes was made at 20 sampling stations in the basin at four seasons (August/2007, November/2007, February/2008, May/2008. Specimens of each species were collected and deposited in the Dárdano de Andrade Lima Herbarium of the Universidade Federal Rural do Semi-Árido; Results: We found 40 species of aquatic macrophytes, in 33 genera and 22 families. The families with the most species were Poaceae and Cyperaceae, and the most species-rich genera were Cyperus and Eleocharis. The most common plant form was amphibian (42.5%), followed by emergent (27.5%), free-floating (12.5%), rooted-submersed (10.0%), and floating-leaved (7.5%). The lowest richness was observed at the estuarine region (3 species), and the highest richness in the upper basin (17 species). The rooted-submersed Hydrothrix gardneri Hooker f. and Ceratophyllum demersum L. were observed in great abundance and frequency in the Santa Cruz Reservoir of Apodi, especially in areas close to cage farms of Nile tilapia (Oreochromis niloticus) (Linnaeus, 1758). The most common free-floating species were Eichhornia crassipes (Mart.) Solms., Pistia stratiotes L., and Salvinia auriculata Aubl., predominantly in stretches that run through urban centers; Conclusion: The species richness of aquatic macrophytes in aquatic environments of the caatinga is similar to that observed in other basins of Brazil. Because of the many dams and reservoirs in the semi-arid Northeast, inventory and monitoring of aquatic macrophytes have become essential, especially in basins that will receive water from the diversion of the São Francisco River.Keywords: aquatic plants, floristic inventory, basin, water diversion, caatinga.Resumo: Objetivo: Nós objetivamos avaliar a riqueza e a distribuição das macrófitas aquáticas nos ambientes aquáticos da bacia hidrográfica do Rio Apodi/Mossoró, no semi-árido do Rio Grande do Norte; Métodos: A investigação da composição florística das macrófitas aquáticas presentes em 20 estações de amostragem da bacia hidrográfica, em quatro épocas do ano (Agosto/2007, Novembro/2007, Fevereiro/2008, Maio/2008. As espécies foram coletadas e depositadas no herbário Dárdano de Andrade Lima da Universidade Federal Rural do Semi-Árido; Resultados: Foram identificadas 40 espécies de macrófitas aquáticas distribuídas em 33 gêneros e 22 famílias. As famílias com o maior número de espécies foram Poaceae e Cyperaceae e os gêneros mais representativos foram Cyperus e Eleocharis. A forma biológica mais freqüente foi a anfíbia (42,5%), seguida pelas emergentes (27,5%); folhas flutuantes (12,5%); submersas enraizadas (10,0%) e com folhas flutuantes (7,5%). A menor riqueza foi observada na região estuarina (três espécies), e a maior riqueza na parte alta da bacia hidrográfica (dezessete espécies). A...