With discovery of four new Neotropical species, the New World shore-fly genus Rhysophora Cresson, 1924 is revised, including a phylogenetic reassessment of some generic relationships within Discomyzini and of species within Rhysophora. The reconstructed phylogenetic relationships are based on 43 adult morphological characters and resulted in the following discoveries, mostly based on the well-supported cladogram: (1) the monophyly of Rhysophora is corroborated; (2) its sister group is Helaeomyia Cresson, not Guttipsilopa Wirth, as previously proposed; (3) three species groups within Rhysophora are recognized; and (4) greater species diversity is in South America, where there is also greater diversity in host plants. We hypothesise that the two Nearctic species, R. robusta and R. laffooni, resulted from two independent dispersal and speciation events when their water lettuce and pickerel weed hosts also dispersed there from the Neotropics. All of these flies are associated with aquatic plants of the families Pontederiaceae (Pontederia, Eichhornia) and Araceae (Pistia stratiotes), with the exception of R. griseola. All species are redescribed and an identification key, distribution maps and illustrations of male terminalia are provided to assist identification of these species.