Ludwigia irregularis (Onagraceae) a rare new species from southern Brazil, and typification of the morphologically similar L. myrtifolia

In this work, we describe a new species of Ludwigia from southern Brazil. We provide a detailed morphological account, field photographs and a distribution map. We also discuss the morphology and taxonomy of the new species in relation to morphologically similar species and assess its conservation status. Finally, we typify the name L. myrtifolia, which refers to the species morphologically most similar to the new species, and we discuss the distribution of this species.