Maize (Zea mays ssp. mays L.) was domesticated from teosinte (Z. mays L. ssp. parviglumis Iltis & Doebley), a plant requiring short day photoperiods to flower. While photoperiod sensitive landraces of maize exist, post-domestication breeding included efforts to grow maize in a broad range of latitudes. Thus, modern maize is often characterized as day-neutral because time to flower is relatively unaffected by photoperiod. We report the first identification of maize constans of Zea mays1 (conz1), a gene with extensive sequence homology to photoperiod genes CONSTANS (CO) in Arabidopsis (Arabidopsis thaliana (L.) Heynh.) and Heading date1 (Hd1) in rice (Oryza sativa L.). conz1 maps to a syntenous chromosomal location relative to Hd1. Additionally, conz1 and two maize homologs of another photoperiod gene exhibit diurnal expression patterns notably similar to their Arabidopsis and rice homologs. The expression pattern of conz1 in long days is distinct from that observed in short days, suggesting that maize is able to discern variations in photoperiod and respond with differential expression of conz1. We offer models to reconcile the differential expression of conz1 with respect to the photoperiod insensitivity exhibited by temperate inbreds.