Graphically enhanced version of a paper published in Castanea, Vol. 66 nos. 1-2, pp. 154–205 (March/June 2001) Photography (with one exception) by James R. Allison and taken in Bibb County unless notated otherwise. All © James R. Allison, 2002. All rights reserved. Note: images labeled with figure numbers appeared (in black and white) in the Castanea article. To see a thumbnail's caption, allow the cursor to hover over the thumbnail. To read a footnote, click on its superscript in the text. Best viewed with Internet Explorer or Netscape, as; some features (e.g., hovering cursor displays caption) may not be supported by other browsers.
Edition of January 16, 2003
Vascular Flora of Ketona Dolomite Outcrops in Bibb County, Alabama
JAMES R. ALLISON* and TIMOTHY E. STEVENS**
*Georgia Department of Natural Resources, Georgia Natural Heritage Program, 2117 U.S. Hwy. 278, SE, Social Circle, Georgia 30025. **Alabama Department of Public Health Laboratories, 8140 AUM Dr., Montgomery, Alabama 36124.
ABSTRACT
Explorations since 1992 in Bibb County, Alabama, have revealed an extraordinary, undescribed glade community developed over the Ketona Formation, an unusually pure dolomite. Eight new endemic taxa were found: Castilleja kraliana, Coreopsis grandiflora var. inclinata, Dalea cahaba, Erigeron strigosus var. dolomiticola, Liatris oligocephala, Onosmodium decipiens, Silphium glutinosum, and Spigelia gentianoides var. alabamensis. In assessing systematic relationships of the Erigeron and Silphium, two additional undescribed taxa, not of Bibb County, were discerned, E. strigosus var. calcicola and S. perplexum. Seven state records were discovered: Solanum pumilum, last collected in 1837 and presumed extinct; Astrolepis integerrima, disjunct from Texas; Paronychia virginica, bridging a gap between Arkansas and Virginia; Baptisia australis var. australis, Rhynchospora capillacea, R. thornei and Spiranthes lucida. More than 60 plant taxa of conservation concern occur on or near these glades, marking them as one of the most significant reservoirs of botanical diversity in the eastern United States.
The eastern United States has been well explored botanically. New species continue to be described every year, but mostly in difficult groups like Carex L. and Isoëtes L., and are usually "split" out of recognized species. The discovery of endemic plant communities with multiple undescribed species mostly occurs in remote regions of South America, Africa, or Southeast Asia.
In 1992 the United States Fish and Wildlife Service contracted with the first author to conduct a status survey in Alabama for Arabis georgiana Harper. As a part of efforts to explore comparatively inaccessible habitats, Allison organized a canoe trip in Bibb County, Alabama, with three friends: the second author and Jim and Debi Rodgers of Senoia, Georgia. By the end of the first morning (May 30), canoe travel had led to the discovery of several previously undocumented populations of Marshallia mohrii Beadle & F. Boynt., a federal Threatened species, on rocky places along the banks of the Little Cahaba River.
At midday, we noticed a strongly sloping, rocky area dominated by herbaceous vegetation, above the right bank of the Little Cahaba River. As we explored the site, it soon became apparent that it supported plant communities distinct from the well studied ones on flat, limestone outcrops ("cedar glades") in Tennessee, Kentucky, Alabama, and Georgia [see ASB Bulletin, vol. 33, no. 4 (1986), for a collection of articles on cedar glades, and Castanea, vol. 59, no. 3 (1994), on the closely related topic of "barrens" vegetation]. Although some of the woody species we saw on glades near the Little Cahaba 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 P. Mill. and Sabal minor (Jacq.) Pers., and particularly two shrubs in the Euphorbiaceae, Leptopus phyllanthoides (Nutt.) G. L. Webster and Croton alabamensis E. A. Sm. ex Chapman var. alabamensis. The herbaceous component, moreover, included a surprising number of unfamiliar taxa, along with recognizable rarities such as Marshallia mohrii. It was clear that this was a natural community that deserved further study.
Upon consulting the most recent statewide Alabama geological map (Szabo et al. 1988), we found that the locations of these glades all fell within a particular mapping unit, Ketona Dolomite. We discovered most of the localities that were not visible from a canoe by studying 1:24,000 topographic maps (on which glades often show as irregular white blotches within green areas) or through examination of infrared aerial photographs. The latter were available for inspection at the USDA Natural Resources Conservation Service office in Centreville, the county seat. Within regions on the photographs that corresponded to the Ketona Formation, as mapped by Szabo et al. (1988), we identified dozens of localities that had a similar appearance to that of known glades. By the time we completed the ground checking of these, we had found approximately 40 sites, defined as outcrops with characteristic flora and separated from each other by at least 0.2 km. For each glade we concocted a name and recorded the endemic, rare, or characteristic Ketona Glade species present.
PHYSICAL CHARACTERISTICS OF HABITAT
This ecosystem is apparently restricted to outcrops in Bibb County, Alabama, 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, within the southern "fringe" of the Ridge and Valley Physiographic Province (Figure 1).
Glades developing on the Ketona Dolomite (Ketona Glades) vary in size from about 0.1 hectare to at least 5 hectares and have a general appearance (Figure 2) resembling the cedar glades developed over limestone or dolomite in Alabama, Georgia, Kentucky, and Tennessee, though they are seldom as level as "classic" cedar glades. The terrain is mostly gently sloping or rolling, but varies from flat to sometimes very strongly sloping. There are 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 marginal ecotones where the glade grades into the surrounding forest. In many areas the bedrock projects above the surrounding surface as low boulders or ledges.
We collected a sample of topsoil from an open area on each of four glades and submitted them through the Cooperative Extension Service of Georgia (University of Georgia/Georgia Department of Agriculture) to the state Soil Testing Laboratory for routine analysis. These tests indicated that the soil derived from the weathering of Ketona Dolomite is very high in magnesium and calcium but low in phosphorus and potassium. The soil reaction is mildly alkaline, with a pH range from 7.4 to 7.6.
The climate of central Alabama is characterized by mild winters, with temperatures often falling below freezing at night but seldom remaining so all day, and warm, humid summers. The physical environment of the Ketona Glades, given its lower latitude, is presumably somewhat milder in winter and warmer in summer than the regions to the north in which glades occur.
BIOLOGICAL COMMUNITIES
The flora of the Ketona Glades is distinguished from those found in other glade, barren, or prairie habitats by containing eight endemic taxa, plus a number of species that are otherwise rare or unknown from glade habitats, along with many taxa well known to frequent such places.
The dominant grass species of the open glade is Schizachyrium scoparium (Michx.) Nash, but it usually does not achieve great density and is an aspect dominant only late in fall and winter, when the strong forb component is muted. Other characteristic plants of this community include Agalinis purpurea (L.) Pennell, A. tenuifolia (Vahl) Raf., Allium canadense L. var. mobilense (Regel) M. Ownbey, Amsonia ciliata Walt. var. tenuifolia (Raf.) Woods., Andropogon gerardii Vitman, A. virginicus L., Asclepias viridiflora Raf., Callirhoë alcaeoides (Michx.) Gray, Castilleja Mutis ex L. f. sp. nov., Cnidoscolus stimulosus (Michx.) Engelm. & Gray, Coreopsis grandiflora Hogg ex Sweet var. nov., Dalea L. sp. nov., Erigeron strigosus Muhl. ex Willd. var. nov., Fimbristylis puberula (Michx.) Vahl, Gaura filipes Spach, Hedyotis nigricans (Lam.) Fosb., Hypoxis hirsuta (L.) Coville, Isoëtes butleri Engelm., Leavenworthia exigua Rollins var. lutea Rollins, L. uniflora (Michx.) Britt., Leptopus phyllanthoides, Liatris Gaertn. ex Schreb. sp. nov., L. cylindracea Michx., Linum sulcatum Riddell var. sulcatum, Lobelia spicata Lam., Marshallia mohrii, Mecardonia acuminata (Walt.) Small var. acuminata, Minuartia patula (Michx.) Mattf., Mirabilis albida (Walt.) Heimerl, Nothoscordum bivalve (L.) Britt., Onosmodium Michx. sp. nov., Oxalis priceae Small ssp. priceae, Paronychia virginica Spreng., Penstemon tenuiflorus Pennell, Polygala boykinii Nutt., P. grandiflora Walt., Rhynchospora colorata (L.) H. Pfeiffer, Rudbeckia triloba L. var. pinnatiloba Torr. & Gray, Ruellia humilis Nutt., Sabal minor, Salvia azurea Lam., Schoenolirion croceum (Michx.) Wood, Scutellaria parvula Michx., Silphium L. sp. nov., Solidago ulmifolia Muhl. ex Willd., Spigelia gentianoides Chapman in A. DC. var. alabamensis K. Gould, Spiranthes magnicamporum Sheviak, Sporobolus junceus (Michx.) Kunth, Tetragonotheca helianthoides L., and Yucca filamentosa L. Also frequent is a moss, Pleurochaete squarrosa (Brid.) Lindb. Amsonia ciliata var. tenuifolia is often abundant and dense enough to be an aspect dominant in spring, and Rudbeckia triloba var. pinnatiloba is occasionally an aspect dominant in summer.
Plants of marginal ecotones or isolated patches where deeper soil has accumulated include Acer leucoderme Small, Asclepias verticillata L., Berchemia scandens (Hill) K. Koch, Bignonia capreolata L., Blephilia ciliata (Pursh) Benth., Carex eburnea Boott, Carya pallida (Ashe) Engl. & Graebn., Celtis tenuifolia Nutt., Cercis canadensis L., Croton alabamensis var. alabamensis, Delphinium carolinianum Walt. ssp. carolinianum, Echinacea purpurea (L.) Moench, Fleischmannia incarnata (Walt.) King & H. E. Robins., Forestiera ligustrina (Michx.) Poir., Frangula caroliniana (Walt.) Gray, Heliopsis helianthoides (L.) Sweet var. gracilis (Nutt.) Gandhi & Thomas, Hypericum frondosum Michx., Ipomopsis rubra (L.) Wherry, Juniperus virginiana, Lithospermum canescens (Michx.) Lehm., Oligoneuron rigidum (L.) Small, Phlox amoena Sims ssp. amoena, Pinus echinata P. Mill., P. palustris, P. taeda L., Quercus muehlenbergii, Rhus aromatica Ait., R. copallinum L., Salvia lyrata L., S. urticifolia L., Scutellaria alabamensis Alexander, S. incana Biehler var. punctata (Chapman) C. Mohr, Sida elliottii Torr. & Gray, Sideroxylon lycioides L., Silene regia Sims, Solanum pumilum Dunal, Symphyotrichum laeve (L.) A. & D. Löve var. concinnum (Willd.) Nesom, S. patens (Ait.) Nesom, S. shortii (Lindl.) Nesom, Thaspium barbinode (Michx.) Nutt. var. chapmanii Coult. & Rose, Toxicodendron radicans (L.) O. Ktze., and Viola walteri House.
A lichen, Psora rubiformis (Ach.) Hooker vel aff., and several ferns are mostly restricted to exposed rocks, usually elevated above the surrounding surface: Asplenium resiliens Kunze, Cheilanthes alabamensis (Buckl.) Kunze, C. lanosa (Michx.) D. C. Eat., and Pellaea atropurpurea (L.) Link. Weathered Ketona Dolomite is dark gray in color, due to one or more unidentified crustose lichens.
A sizeable proportion of the species mentioned in the preceding paragraphs of this section are regularly found on and around limestone glades (or cedar glades; we use the terms interchangeably). In numbers of endemics, numbers of outcrops and in their aggregate area, cedar glades are best developed in the Nashville Basin of Middle Tennessee (Quarterman 1950). The characteristic cedar glade flora is also well established on glades found in northwestern Alabama and northwestern Georgia, as well as in some southeastern states more remote from Alabama, especially Kentucky, but also Virginia and West Virginia (Baskin and Baskin 1986, Bridges and Orzell 1986). Despite having many widespread calciphilic and/or xerophytic plant taxa in common, the Ketona Dolomite Glade flora is distinct from that of cedar glades, not only because of the endemic or other characteristic elements present in the Ketona Glade flora and absent from limestone glades, but conversely, by the sizeable number of endemic or characteristic elements of the limestone glade flora that are missing from the Ketona Glades. Cedar glade taxa occurring in both Middle Tennessee and northern Alabama that are absent or essentially so from the Ketona Glades include Allium cernuum Roth, Astragalus tennesseensis Gray ex Chapman, Astranthium integrifolium (Michx.) Nutt., Dalea gattingeri (Heller) Barneby, Delphinium carolinianum Walt. ssp. calciphilum Warnock [D. virescens auct. non Nutt.], Eurybia hemispherica (Alexander) Nesom [Aster hemisphericus Alexander], Grindelia lanceolata Nutt., Heliotropium tenellum (Nutt.) Torr., Hypericum dolabriforme Vent., H. sphaerocarpum Michx., Lobelia appendiculata A. DC. var. gattingeri (Gray) McVaugh, Oenothera triloba Nutt., Onosmodium molle Michx. ssp. molle, Pediomelum subacaule (Torr. & Gray) Rydb., Ratibida pinnata (Vent.) Barnh., Rudbeckia triloba L. var. triloba, Sedum pulchellum Michx., Symphyotrichum priceae (Britt.) Nesom [Aster priceae Britt.], Talinum calcaricum Ware, Verbena simplex Lehm., and Viola egglestonii Brainerd.(1) Furthermore, the dominant grass species of the Ketona Glades is Schizachyrium scoparium, a perennial, while the dominant grass of cedar glades is Sporobolus vaginiflorus (Torr. ex Gray) Wood, an annual that is rarely found on Ketona Glades except in places disturbed by humans.
Baskin et al. (1994) attempted to resolve inconsistencies in the use of such terms as "glades," "barrens," and "limestone prairies" that have been used in discussing openings, dominated by grasses and forbs, that are developed over calcareous bedrock. They devised over a dozen criteria useful for assigning such places to one of three general categories: limestone glade, xeric limestone prairie, or barrens. The Ketona Glades fail several to many criteria for each of their three categories, but come closest to the "xeric limestone prairie" class. Since they differ from limestone prairies by developing over dolomite rather than limestone, by containing multiple endemics, and by supporting two species of Leavenworthia, the simplest course would be to establish a fourth category to accommodate the Ketona Glades.