Resumo. Phanaeini is a New World tribe of scarab beetles (Coleoptera: Scarabaeidae: Scarabaeinae) whose members are noteworthy for their iridescence—the phenomenon that a color changes as the angle at which it is viewed changes. Iridescence has evolved independently in various clades of animals, including multiple clades of arthropods. Recently, a team of researchers have described the microstructure of the elytra (the hardened forewing) of the iridescent beetle Chrysina gloriosa (LeConte, 1854) (Scarabaeidae: Rutelinae). The North American Phanaeus vindex MacLeay, 1819 also displays iridescence; however, the microstructure of P. vindex’s elytra has not yet been elucidated. The null hypothesis is therefore that the elytra of P. vindex is the same microstructurally as that of C. gloriosa. Following analysis, we have accepted the null hypothesis: P. vindex displays elytral hexagonal cells called "conic focal domains" that, when viewed from above, are microstructurally similar to those of C. gloriosa. The subfamily that is sister to Rutelinae, Dynastinae, is non-iridescent and also lacks domains in its elytra, giving further evidence to the hypothesis that the domains are responsible for iridescence.