Abstract: Huoshan County, located in the hinterland of the Dabie Mountains of Anhui Province, occupies a major floristic transition between northern subtropical and warm-temperate regions and supports substantial plant diversity. This study characterized vascular plant diversity, floristic composition, and tree species composition using three surveys of forest and grass germplasm resources conducted from November 2023 to August 2024 with combined line-transect and quadrat sampling. A total of 1 396 vascular plant species representing 621 genera and 141 families were recorded. Asteraceae, Rosaceae, Poaceae, and Fabaceae were the most species-rich families, and herbaceous taxa comprised 808 species, accounting for 57.88% of the total flora. Floristic composition showed diverse biogeographic distribution patterns. At the family level, nine distribution types and eight subtypes were identified, with tropical elements comprising 63.16% of non-cosmopolitan families. At the genus level, 15 distribution types and 13 subtypes were recognized, and temperate elements accounted for 60.51% of non-cosmopolitan genera. The coexistence of substantial tropical and temperate components reflects the transitional floristic character of Huoshan County between northern subtropical and warm-temperate zones. Each of the 54 tree quadrats contained 23–36 plant species and collectively included 88 tree species belonging to 61 genera and 38 families. Phyllostachys edulis (Carrière) J. Houz., Liquidambar formosana Hance, and Pinus massoniana Lamb. had the highest importance values at 20.2%, 8.36%, and 7.47%, respectively. These findings demonstrate the high vascular plant diversity and distinct biogeographic structure of Huoshan County and provide a scientific basis for the conservation, management, and sustainable utilization of plant germplasm resources in the Dabie Mountains.