Abstract
The genus Nymphoides is a freshwater aquatic dicot represented by two species in Iran. Based on our current regional taxonomic revision of this genus, we recognize Nymphoides cristata, previously identified as Nymphoides indica in Flora Iranica. However, these species are easily distinguished from each other by having crested petal lobes in the latter. We investigated the morphology and anatomy of Nymphoides cristata and Nymphoides peltata. The most important morphological features for differentiation between these species are corolla color and inflorescence type. The anatomy of cross-sections of leaf, petiole, stem and the surface sections of leaf were studied. The following characters were found to be taxonomically informative: the presence of stellate, polyramous and ramiform foliar sclereids as well as the presence of astrosclereids in petioles and stems of both examined taxa, while spheroidal sclereids are only observed in the stems of Nymphoides peltata.