Apart from the Atlantic and Gulf coastal plain, this zone includes a large part of the eastern United States. In the north it extends into southern Canada to include southeastern Ontario and southern Quebec, while in the south it extends to central Georgia, central Alabama, parts of eastern Texas and includes much of Arkansas. Its western boundary extends to Minnesota, eastern Iowa, the Ozark Plateau and the Quachita Mountains.

Appalachian Shale Barrens

In the mid-Appalachian region there are a series of Palaeozoic shale outcrops known as the Shale Barrens. In contrast to the surrounding woodlands, these support relatively sparse vegetation. This is mainly due to their low nutrient status, lack of moisture, high temperatures and insolation levels. In fact, the habitat has been described as an eastern counterpart of North America’s western deserts. These peculiar conditions have led to the development of about 18 endemic taxa including two palaeoendemics Phlox buckleyi (Polemoniaceae) and Trifolium virginicum (Fabaceae), seven neoendemics Allium oxyphilum (Alliaceae), Arabis serotina (Brassicaceae), Astragalus distortus, var. distortus (Fabaceae), Aster schistosus (Asteraceae), Clematis coactilis, C. viticaulis (Ranunculaceae) and Solidago arguta var. harrisii (Asteraceae), six holoendemics (Calystegia spithamaea subsp. purschiana (Convolvulaceae), Clematis ablicoma (Ranunculaceae), Eriogonum allenii (Polygonaceae), Paronychia Montana (Caryophyllaceae), Pseudotaenidia montana (Apiaceae) and Senecio antennariifolius (Asteraceae), two patroendemics (Antennaria virginica (Asteraceae) and Oenothera argillicola (Onagraceae) and one apoendemic Helianthus laevigatus (Asteraceae). All of these are obligate heliophytes and it seems that the high levels of exposure to sunlight has been one of the main driving forces behind the creation of these endemics.

References

Keener, C. S. 1983. Distribution and biohistory of the endemic flora of the Mid-Appalachian Shale Barrens. The Botanical Review, 49: 65-115.