Floristic survey of aquatic macrophytes in eastern Maranhão, Brazil: richness, biological forms and three new records

The aim of this study was to carry out a floristic survey of aquatic macrophytes in the municipality of Chapadinha, eastern Maranhão, and classify their biological forms. The study was done between September 2021 and September 2022. A total of 31 families, 49 genera and 72 species of aquatic macrophytes were catalogued, of which 65 are angiosperms. Among them, Bacopa stricta (Plantaginaceae), Staurogyne diantheroides (Acanthaceae), and Xanthosoma aristeguietae (Araceae) are new records for the flora of Maranhão, with the last two new records for Northeast Brazil. The richest family was Cyperaceae, with 11 species, followed by Plantaginaceae (seven taxa), Fabaceae (five taxa) and Lentibulariaceae (five taxa). Six biological forms were recorded, amphibious (27 taxa) and emergent (26 taxa) being the most common. The aquatic environments of Chapadinha are home to a considerable number of species, families, and life forms of macrophytes. The results show that due to the lack of surveys, evidenced by the new records presented, the state aquatic flora is still underestimated. Further studies in poorly explored areas are suggested, especially in the eastern part of the state, to improve understanding of species richness.