The taxonomic treatment for the family Pontederiaceae in the coastal region of Piauí is presented as a contribution to knowledge of the biological diversity of the state. Five species were identified in three genera, Eichhornia Kunth, Heteranthera Ruiz & Pav. and Pontederia L. Eichhornia is represented by three species, E. azurea (Sw.) Kunth, E. crassipes (Mart.) Solms and E. diversifolia (Vahl) Urb., while Pontederia and Heteranthera are represented by a single species each, P. cordata var. ovalis (Mart.) Solms and H. rotundifolia (Kunth) Griseb., respectively. All species are native but not endemic to the region. Three species are new records for Piauí. Descriptions, illustrations and an identification key to the species are provided, together with information on their geographical distribution and habitats.
Aquatic macrophytes; biodiversity of Piauí; Delta do Parnaíba
