Field and chemical studies have shown that female bees of the genus Macropis (Melittidae) visit flowers of Lysimachia (Primulaceae) in the New World in order to collect liquids secreted by trichome elaiophores at the bases of the petals and/or anther filaments. The association between the genera is not obligatory on the part of the plants. Several New World species are restricted to areas without Macropis. All New World taxa appear to reproduce vegetatively via rhizomes and can apparently be pollinated by other bees. While reports are few, they indicate dependency of Macropis on Lysimachia and suggest a predominant association with L. ciliata.