A BOTANICAL "LOST WORLD" IN CENTRAL ALABAMA
James R. Allison
The eastern United States, like Europe, has been well explored botanically. New species continue to be described every year, but mostly in difficult groups like Carex and Isoetes, or are "split" out of recognized species. The discovery of endemic plant communities with multiple undescribed species mostly occurs in remote jungles of South America, Africa, or Southeast Asia.
In 1992, the U.S. Fish and Wildlife Service contracted with me to conduct a Status Survey in Alabama for Arabis georgiana Harper. Hoping to explore comparatively inaccessible habitat, I organized a canoe trip in Bibb County, Alabama with three friends (Tim Stevens, Jim and Debbie Rodgers). This proved to be a useful means for finding undocumented populations for the rare Arabis, and incidentally resulted in a significant discovery.
At midday of May 30, 1992, we noticed a strongly sloping "cedar glade" above the right bank of the Little Cahaba River. Exploring the site, we discovered a glade community unlike any that had been described from Alabama, Georgia or Tennessee. Although the woody species were typical of calcareous glades and barrens (e.g., Juniperus virginiana L., Quercus muehlenbergii Engelm.), there were others that would have marked this as a distinctive glade community even in winter, such as Pinus palustris Miller and Sabal minor (Jacq.) Pers. The herbaceous component, moreover, included an astonishing assemblage of undescribed taxa and other rarities. It was evident that this was a natural community that would warrant further study.
This glade community in Bibb County, Alabama, is apparently restricted to at least 40 outcrops of the Ketona Formation, an unusually pure dolomite of Upper Cambrian age (Rheams 1992). These are all within a zone about 18 km long and at most about 0.8 km wide, near the southern terminus of the Ridge and Valley Physiographic Province.
Most of the additional localities not visible from a stream navigable by canoe were discovered by using 1:24,000 topographic maps (glades often show as white blotches in otherwise green areas) or through examination of infrared photography. The latter was available at the USDA Soil Conservation Service Office in Centreville, Alabama. Floristic lists were compiled for each glade and specimens of unknown taxa collected for later identification.
Samples of soil were collected from of four glades and submitted through the Cooperative Extension Service (University of Georgia, Georgia Dept. of Agriculture) to the state Soil Testing and Plant Analysis Laboratory for routine analysis.
Glades on the Ketona Dolomite (Ketona Glades), had a general appearance resembling the well known "cedar glades" developed over limestone or dolomite in Alabama, Georgia, Kentucky and Tennessee. Sites varied in size from about 0.1 hectare to at least 5 hectares. The terrain varied from flat to rolling, with a maximum incline of about 45 degrees. There were patches of exposed bedrock, thin-soiled areas dominated by grasses and other herbaceous vegetation, variously sized islands and peninsulas of woody vegetation where soil has accumulated to greater depth, and ecotone areas where the glade grades into the surrounding forest. In some places, the bedrock projected above the surrounding surface in the form of low boulders or ledges.
Soil tests indicated that the soil derived from the weathering of Ketona Dolomite was very high in magnesium and calcium but low in phosphorus and potassium. The soil reaction was somewhat basic, with a pH range from 7.4 to 7.6.
The flora of the Ketona Glades was distinguished from those found in other glade, barren, or prairie habitats by the presence of six narrowly endemic taxa and a sizeable number of species that were otherwise rare or unknown in glade habitats, in association with taxa of widespread occurrence on calcareous glades and barrens.
Open Glade Habitats. Characteristic plants of the open glade included Agalinis setacea (J.F. Gmel.) Raf., A. tenuifolia (Vahl) Raf., Allium canadense var. mobilense (Regel) M. Ownbey, Amsonia ciliata var. filifolia Woods., Andrachne phyllanthoides (Nutt.) Coult., Andropogon gerardii Vitman, A. virginicus L., Arenaria patula Michx., Asclepias viridiflora Raf., Callirhoe alcaeoides Nutt., Castilleja kraliana J. R. Allison ined., Cnidoscolus stimulosus (Michx.) Engelm. & Gray, Coreopsis grandiflora var. harveyana (Gray) Sherff, Dalea cahaba J. R. Allison ined., Erigeron strigosus var. dolomiticolus J. R. Allison ined., Fimbristylis puberula (Michx.) Vahl, Gaura filipes Spach, Houstonia nigricans (Lam.) Fern., Hypoxis hirsuta (L.) Cov., Isoetes butleri Engelm., Leavenworthia exigua var. lutea Rollins, L. uniflora (Michx.) Britt., Liatris cylindracea Michx., L. oligocephala J. R. Allison ined., Linum sulcatum Ridd., Lobelia spicata Lam., Marshallia mohrii Beadle & Boynt., Mecardonia acuminata (Walt.) Small, Mirabilis albida (Walt.) Heimerl, Nothoscordum bivalve (L.) Britt., Onosmodium decipiens J. R. Allison ined., Oxalis priceae ssp. priceae Small, Paronychia virginica Spreng., Penstemon tenuiflorus Penn., Pleurochaete squarrosa (Brid.) Lindb., Polygala boykinii Nutt., P. grandiflora Walt., Rhynchospora colorata (L.) Hitchc., Rudbeckia triloba var. pinnatiloba T. & G., Ruellia humilis Nutt., Sabal minor, Salvia azurea Lam., Schoenolirion croceum (Michx.) Wood, Scutellaria parvula Michx., Silphium glutinosum J. R. Allison ined., Solidago ulmifolia Muhl. ex Willd., Spigelia gentianoides Chapm., Spiranthes magnicamporum Sheviak, Sporobolus junceus (Michx.) Kunth, Tetragonotheca helianthoides L. and Yucca filamentosa L.
Ecotone Habitats. Plants of marginal areas or isolated patches where deeper soil had accumulated included Acer leucoderme Small, Asclepias verticellata L., Aster attenuatus Lindl., A. patens Ait., A. shortii Lindl., Berchemia scandens (Hill) K. Koch, Bignonia capreolata L., Blephilia ciliata (Pursh) Benth., Bumelia lycioides (L.) Pers., Carex eburnea Boott, Carya pallida (Ashe) Engl. & Graebn., Celtis tenuifolia Nutt., Cercis canadensis L., Croton alabamensis E. A. Smith, Delphinium carolinianum Walt., Echinacea purpurea (L.) Moench, Forestiera ligustrina (Michx.) Poir., Heliopsis gracilis Nutt., Hypericum frondosum Michx., Ipomopsis rubra (L.) Wherry, Juniperus virginiana, Lithospermum canescens (Michx.) Lehm., Phlox amoena Sims, Pinus echinata Miller, P. palustris, P. taeda L., Quercus muehlenbergii, Rhamnus caroliniana Walt., Rhus aromatica Ait., R. copallina L., Salvia lyrata L., S. urticifolia L., Scutellaria alabamensis Alex., S. incana Biehler, Sida elliottii T. & G., Silene regia Sims, Solanum pumilum Dunal, Solidago rigida L., Thaspium barbinode var. chapmanii Coult. & Rose, Toxicodendron radicans (L.) O. Ktze. and Viola walteri House.
Ledges and Boulders. Several ferns and a lichen were mostly restricted to exposed rocks, usually elevated above the surrounding surface: Asplenium resiliens Kunze, Cheilanthes alabamensis (Buckl.) Kunze, C. lanosa (Michx.) D. C. Eat., Pellaea atropurpurea (L.) Link and Psora rubiformis (Wahl.) Hook.
Undescribed Taxa. Six endemic taxa new to science were the most distinctive elements of the flora. They will be described in another paper. Two of these, an Onosmodium and a variety of Erigeron strigosus Muhl. ex Willd., were strongly characteristic of Ketona Glades, being abundant at virtually every site. A Dalea (Petalostemum) also was frequent but failed to reach the glades near the western periphery of the Ketona region. Near the center of the Ketona region, where the glades were most numerous and achieved their greatest areal extent (and correspondingly the flora was best developed), a species of Castilleja was frequent. Nested within its range was the rarest of the new taxa, an undescribed Liatris. Finally, a distinctive species of Silphium occurred on the majority of glades and also in rocky areas along Bibb County streams outside the Ketona zone, where it grows on soil derived from other dolomites or from limestone.
State Records. A total of eight state records were collected in the course of this study: Solanum pumilum [S. carolinense var. hirsutum (Nutt.) A. Gray], a candidate for listing under the Endangered Species Act (Candidate Species), previously known only from two Georgia collections of the 1830s; nationally Endangered Spigelia gentianoides, which had been thought to be restricted to the Florida Panhandle, where it was considered nearly extinct; Rhynchospora thornei Kral, a Candidate Species known previously from only four collections from three states; R. capillacea Torr. and Spiranthes lucida (H. H. Eat.) Ames, both disjunct from Tennessee where they are very rare; Paronychia virginica, bridging a gap between Virginia and Arkansas; Astrolepis integerrima (Hook.) Benham & Windham, disjunct from Texas; and Baptisia australis (L.) R. Br., already known from the adjoining states of Georgia and Tennessee.
Other Rare Taxa. County Records from the Ketona Glades include nationally Endangered Xyris tennesseensis Kral, previously known in Alabama from a small population about 160 km to the northwest; two Candidate Species, Aster georgianus Alex. and Leavenworthia exigua var. lutea; and 11 other rarities tracked by the Alabama Department of Conservation and Natural Resources, Natural Heritage Section (ANHS).
Other rare taxa of these glades that had been collected previously in Bibb County included Marshallia mohrii, a national Threatened Species achieving its greatest abundance on these glades; Silene regia, a species that had been feared extinct in Alabama; and 13 other species tracked by ANHS not yet mentioned, including three Candidate Species (Arabis georgiana, Croton alabamensis, Rudbeckia triloba var. pinnatiloba).
Within 100 meters of one or more Ketona Glades occur at least 13 other rarities, including Veratrum woodii J. W. Robbins, known previously in Alabama from a single population more than 240 km to the southeast), and four more Candidate Species: Jamesianthus alabamensis Blake & Sherff, a species that had been thought to be endemic to a tiny area in Alabama more than 175 km to the northwest; Aquilegia canadensis var. australis (Small) Munz, disjunct from the Florida Panhandle; Neviusia alabamensis A. Gray, a species known from only 15 other populations; and Sedum nevii A. Gray.
The Ketona Glades contain one of the most significant reservoirs of biological diversity in the eastern United States, with at least 56 rare taxa found on or near them. A reasonable explanation for the existence of this extraordinary assemblage is a combination of edaphic specialization, geographic isolation, relictualism, and chance dispersal events.
Magnesium is an essential plant nutrient but considered toxic in high concentrations, when it interferes with the uptake of other essential elements. The combination of high magnesium levels with low levels of potassium and phosphorus in a shallow, droughty soil produces conditions only specially adapted plants can tolerate. The result is a community of narrow endemics and (presumably) ecotypes of wide-ranging species, evolving in the absence of competition from more generally adapted types.
High magnesium levels in droughty soils are partly responsible for the development of an endemic flora in certain other habitats, such as serpentine barrens. The latter habitat is quite different from Ketona Dolomite glades in other respects, however, perhaps most importantly in the presence of heavy metals, such as chromium, and in pH, serpentine soils being generally acidic while dolomitic soils are basic. Because the Ketona Formation is restricted to central Alabama and other rocks as high in magnesium, such as serpentine, are unknown in Alabama, at least as pavements (Adams et al. 1926), this community is isolated both geographically and edaphically.
Some of the rare elements of the flora, such as the new Silphium, may once have been more widespread, persisting in that portion of the Ridge and Valley that would likely have experienced the mildest climate during the Pleistocene. Others, such as Astrolepis integerrima, appear to represent long-distance immigration.
Partial funding of this project was provided by the U.S. Fish and Wildlife Service (Grant No. 1448-0004-93-926). Special thanks go to Tim Stevens for his assistance in the field throughout the course of this study.
Adams, G. I., C. Butts, L. W. Stephenson and W. Cooke. 1926. Geology of Alabama. Geological Survey of Alabama, Special Report No. 14.
Rheams, K.F. 1992. Mineral resources of the Valley and Ridge province, Alabama. Geological Survey of Alabama, Bulletin 147.