Cowleech Prairie Preserve, located on the Cowleech Fork of the Sabine River, Hunt County, northeastern Texas, is a wet-to-mesic blackland prairie-wetland complex that represents a plant community currently undescribed by the National Vegetation Classification. However, it bears similarities with those globally imperiled communities having eastern gamagrass (Tripsacum dactyloides) as a first-order dominant. Objectives of this study were to document floristic composition and examine changes in composition and dominance of species from late spring to early autumn and to better define classification of this community as a recognized association. We collected data on species richness, composition, ground cover, and abundance of forbs during early autumn 2003 and late spring 2004. Total number of species (species richness) recorded was 56 in autumn and 61 in spring. However, these seasonal differences in species richness were not significant. Poaceae (grasses) was the most dominant family in autumn, with gamagrass forming the most predominant ground cover. In contrast, sedges and forbs were dominant in spring. Many species of forbs (47.0% in spring and 62.0% in autumn) had a limited distribution among transects, occurring in only one of five transects during the two seasons. In addition, 21.4 and 29.5% of species of forbs were unique to autumn and spring, respectively. Beautiful false dragon-head (Physostegia pulchella), a species endemic to the blackland prairies of Texas, was recorded in spring. This study represents the first comprehensive floristic documentation of the Cowleech Prairie Preserve.