The Botanical Review

, Volume 49, Issue 1, pp 65–115 | Cite as

Distribution and biohistory of the endemic flora of the mid-Appalachian shale barrens

  • Carl S. Keener


The mid-Appalachian shale barrens, first described by E. S. Steele in 1911, range within the eastern United States from south-central Pennsylvania to southwestern Virginia and adjacent West Virginia. These Paleozoic shaly outcrops are characterized by a steep southern exposure, typically an undercutting stream at the base, and a relatively sparse vegetation cover in contrast to the surrounding woodlands of the eastern deciduous forest. Lithologically, the barrens have thin, fissile, variously colored shale and siltstone fragments intermixed with sandstones and minor conglomerates. At least some of the barrens were colonizable sites since the late Tertiary. The sparsity of herbaceous vegetation is due chiefly to high insolation temperatures and low moisture conditions at the surface of the barrens, two physical parameters which eliminate most young seedlings. In addition to adapting to these severe constraints, the shale barren endemics require adequate root space, and, as obligate heliophytes, high sunlight intensity. Eighteen taxa are recognized as endemic to the shale barren region. Two (Phlox buckleyi, Trifolium virginicum) are paleoendemics, seven (Allium oxyphilum, Arabis serotina, Astragalus distortus var.distortus, Aster schistosus, Clematis coactilis, C. viticaulis, Solidago arguta var.harrisii) are neoschizoendemics with restricted ranges, six (Calystegia spithamaea ssp.purshiana, Clematis albicoma, Eriogonum allenii, Paronychia montana, Pseudotaenidia montana, Senecio antennariifolius) are holoschizoendemics, two (Antennaria virginica, Oenothera argillicola) are patroendemics which are ancestral to two or more species, and one (Helianthus laevigatus) is an apoendemic polyploid derivative. Possibly as many as six taxa (Antennaria virginica, Astragalus distortus var.distortus, Clematis albicoma, Eriogonum allenii, Oenothera argillicola, Senecio antennariifolius) are disjunct endemics with the vicariad in mid-central to western North America. The eighteen endemics are not equally distributed throughout the shale barren region, a fact which may reflect unequal evolutionary age, dissemination, and breeding structure. In general, speciation of the endemics appears to be largely an initial migration (from the southwestern United States) and geographic isolation of diploid populations or ecotypic differentiation of subsets of adjacent species within the Appalachian forests. Conservation of these endemics is strongly recommended.


Chromosome Number Botanical Review North American Species Serpentine Soil Paronychia 
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© The New York Botanical Garden 1983

Authors and Affiliations

  • Carl S. Keener
    • 1
  1. 1.202 Buckhout LaboratoryThe Pennsylvania State UniversityUniversity Park

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