Lycaena acmon Westwood, 1852 is based on a painting and plate legend in Westwood and Hewitson’s Genera of Diurnal Lepidoptera. The specimen illustrated was located in the British Museum Natural History and is the holotype by monotypy. The accompanying plate legend gives “California” as the type locality. Because the butterfly is a member of a complex of species, now considered in the genus Plebejus (Opler and Warren, 2003), that requires much systematic study, and some confusion exists on the identity of L. acmon, it is necessary to fix a more specific type locality, to characterize the species, and to present its synonymy. In addition, a number of taxa described or cited as P. acmon are listed, but which likely represent other species
