Genetic analysis of day-neutral (photo-insensitive) cultivars and their derivatives hybridized to standard short-day clones of octoploid strawberries [Fragaria × ananassa Duchn., F. chiloensis (L.) Duchn., and F. virginiana glauca Staudt., x = 7, 2n = 56] revealed that photo-insensitivity is controlled by a single dominant allele of a Mendelian gene. The dominant genetic trait is expressed in hybrids with other Fragaria spp. Intergeneric hybrids of day-neutral Fragaria and short-day Potentilla glandulosa L. and P. fruticosa L. also express photo-insensitivity. The day-neutral genes in European perpetual flowering (photo-insensitive) diploid `Alpine' F. vesca (2N = 14) apparently have evolved independently, since photo-insensitivity is recessive to photo-sensitivity. Native California diploid F. vesca have diverged considerably from European F. vesca. No photo-insensitive diploids have been found among them. Photo-sensitivity in native California F. vesca is controlled by three dominant genes. The origins of day-neutral cultivars of F. × ananassa and the classification of day-neutrality are discussed.