Graphically enhanced version
of a paper published in
Castanea, Vol. 66 nos. 1-2, pp. 154–205
Photography (with one exception) by James R. Allison
and taken in Bibb County unless notated otherwise.
All © James R. Allison, 2002. All rights reserved.
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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
2117 U.S. Hwy. 278, SE, Social Circle, Georgia 30025.
**Alabama Department of Public Health Laboratories,
8140 AUM Dr., Montgomery, Alabama
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
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
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
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
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),
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
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
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.
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
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
grandiflora Walt., Rhynchospora colorata (L.) H. Pfeiffer, Rudbeckia triloba L. var. pinnatiloba
Torr. & Gray, Ruellia humilis Nutt., Sabal minor, Salvia azurea Lam.,
(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
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
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