Physaria ludoviciana (Brassicaceae) is rare in Illinois, Minnesota, and Wisconsin. Environmental effects on floral development are unclear. Both self-compatibility and self-incompatibility occur within Physaria species. Objectives were to describe flowers, to determine how photoperiod affects flower development, and to predict whether flowers are self-compatible or self-incompatible. For photoperiods, greenhouse-grown plants were placed in either 16 or 8 hr photoperiods. Inflorescences and open flowers were counted weekly. For pollination, flowers were self-pollinated or cross-pollinated. Plants developed inflorescences after 20 and 28 d in long and short days, respectively. Inflorescences/plant increased for both photoperiods throughout the study. In short days, plants produced more inflorescences (10.8/plant) than in long days (7.1/plant). Anthesis started at 48 and 56 d for long and short days, respectively. Blooming peaked at 83 d (4.9 flowers/plant/day) for long days, and at 98 d (3.5 flowers/plant/day) for short days. Cross-pollinated flowers produced fruits, while self-pollinated ones did not.