How specialist bees distinguish their host plants from co-blooming non-hosts is not well understood, but it is thought that they may be physiologically limited in their ability to recognize the majority of visual and olfactory cues presented by flowering plants. Species in the genus Diadasia collect pollen from just one of five plant families: Cactaceae, Malvaceae, Onagraceae, Asteraceae, and Convolvulaceae. Assuming a common ancestor for all Diadasia specialized on just one plant, this indicates host-switches in the past, and an ability to recognize more than one flowering plant. I hypothesized that host plants of Diadasia share the same visual and olfactory cues, thus enabling past host-switching to novel plant families, and that co-blooming non-hosts are highly dissimilar in terms of scent and visual appearance. I determined the compounds associated with the scent of Malvaceae and Cactaceae host flowers of North American Diadasia. I also evaluated visual cues for these flowers by measuring their full spectrum of reflected wavelengths, as well as select morphometric characters. I determined whether host flowers, regardless of taxa, were more similar to each other than non-hosts that were co-blooming and attractive to other bee species. Finally, I performed electroantennographic and behavioral experiments to assess the relative importance of these cues (visual and olfactory) in natural settings. Diadasia host plants share some chemical and visual characteristics that may in part explain the radiation of this group onto these particular hosts. First, host plants share a suite of scent compounds that are among the least variable across species. Many of these elicited antennal responses and did not decrease visitation when applied to host flowers. In contrast, some compounds produced by non-host flowers are detectable to Diadasia, but Diadasia are repelled by them when they are applied to host flowers. Diadasia host flowers do not share a color profile in common, but there is more reflectance in the bee-uv range as compared to other regions of the light spectrum. Also, Diadasia host flowers have a more contrasting central area that is relatively larger than in non-hosts.