Coreopsis rosea is important as a landscape plant and is of some impor-tance for restoration of native species. In both situations it is important to understand the breeding system so that the pollination process may be controlled for optimal seed production. The study of the incompatibility system is important to seed production. In commercial crops, seeds may be products of open pollination or F1 hybrids. In the former, genetic variability exists. In conservation and recovery programs of local flora, seeds with genetic variability are desirable. In development of commercial crops, uniform seeds and plants are desirable. Regardless of whether seeds will ultimately be used for commercial crops or for species restoration, an understanding of self-incompatibility will allow the pollination process to be manipulated for optimal seed production. The purpose of this research was to investigate the sexual reproduction mode in Coreopsis rosea. The objectives were to determine whether Coreopsis rosea operates with a self-incompatibility system, and, if so, to discover whether it is a sporophytic or gametophytic mode. The sporophytic form of self-incompatibility has been found in other plants in the Asteraceae family, but no one has studied self-incompatibility in Coreopsis rosea. The purpose of this research was to identify the self-incompatibility system in Coreopsis rosea. A series of self- and cross-pollinations were made in situ, and in vivo pollinations were made and the pistils studied under the microscope. Results indicate that Coreopsis rosea is self-incompatible and operates under the sporophytic mode.