The purpose of this application, under Article 75.5 of the Code, is to conserve the widely used name Chrysophanus florus Edwards, 1884 (currently Lycaena florus) for a butterfly species from North America by designating a neotype for Polyommatus castro Reakirt, 1866. The identity of Polyommatus castro (currently Lycaena castro) is uncertain because its lectotype is similar to the widespread lowland Lycaena helloides (Boisduval, 1852) in one trait and similar to the high-altitude Rocky Mountains butterfly Lycaena florus (Edwards, 1884) in another trait, and it lacks precise locality data that could have indicated its identity. A male of L. helloides is proposed as the neotype of L. castro, which will both fix the identity of L. castro as L. helloides, a synonymy accepted for 102 years, and conserve the name Chrysophanus florus Edwards, 1884 (currently Lycaena florus), which has been used for 125 years for the high-altitude butterfly and has been used in most of the scientific papers on the species.