ABSTRACT The Cucumber Creek Nature Preserve is located in the Ouachita Mountains of southeastern Oklahoma, a region of high plant diversity in the state. An inventory of the preserve yielded 341 taxa of vascular plants in 231 genera and 98 families. The largest families were the Asteraceae (46) and Poaceae (27). The flora consisted of 52 annuals, 1 biennial, 287 perennials, and 95 woody taxa. Sixteen exotic species were collected, representing 4.7% of the flora. Twenty-five species were present that are tracked by the Oklahoma Natural Heritage Inventory: Actaea pachypoda, Carex cephalophora, C. latebracteata, C. ouachitana, C. striatula, Castanea pumila var. ozarkensis, Chionanthus virginicus, Dirca palustris, Fraxinus quadrangulata, Galium arkansanum, Halesia tetraptera, Hamamelis vernalis, H. virginiana, Hypericum gentianoides, Ilex opaca, Iris cristata, Magnolia tripetala, Mitchella repens, Panax quinquefolius, Piptochaetium avenaceum, Polygala polygama, Ribes cynosbati, Spigelia marilandica, Stachys eplingii, and Uvularia grandiflora.