The aquatic plant genus Sagittaria contains about 35 species and is distributed mostly in the New World but can also be found in Europe and Asia. Sagittaria was analyzed phylogenetically using sequences of the 5S nuclear ribosomal non-transcribed spacer (5S-NTS). Taxa that have historically been placed in Sagittaria subgenus Lophotocarpus, with the exception of members of the Sagittaria subulata group, were strongly supported as monophyletic and were placed basal to the remainder of the genus when using the closely related genus Echinodorus (Alismataceae) for outgroup comparison. Of the remaining taxa, sagittate leaved species form a group that is sister to non-sagittate leaved species. The sagittate leaved group has a disjunct distributional pattern between the New World and Asia in which the Asian species appear to be the basal members. The Sagittaria subulata group, within the non-sagittate leaved species, is strongly supported as monophyletic. Taxonomy, character evolution, biogeography of Sagittaria will be discussed in light of these findings.

Key words: 5S-NTS, Lophotocarpus, monophyletic, Sagittaria, sagittate