Several botanists in the past have recognized the southeastern unglaciated part of Ohio as a unique area in the state. A rather large number of southern species of vascular plants grow there. Based on evidence aggregated from various sources, 169 taxa are designated as being characteristic or definitive of this region. Most of these plants are representatives of the, flora of the Appalachians, the Piedmont and the Cumberland Mountains. Many have probably migrated to southeastern Ohio via the ancient Teays River Valley. Their distribution patterns in Ohio assist in the delimitation of this region, as a distinct phytogeographic unit.