Taxonomy and distribution of Sagittaria (Alismataceae) in north-eastern Brazil

The family Alismataceae comprises 12 genera of herbaceous aquatic plants. There are only two genera that are naturally found in Neotropical regions: Echinodorus and Sagittaria. This study examines the species of Sagittaria from north-eastern Brazil, a region that is characterized by a semiarid climate and intermittent aquatic ecosystems. Four taxa have been identified: S. guayanensis subsp. guayanensis, S. rhombifolia, S. lancifolia subsp. lancifolia and S. planitiana. Full descriptions, observations, geographic distributions, illustrations and a species key are presented.