''Asplenium'' × ''kentuckiense'', commonly known as Kentucky spleenwort, is a rare, sterile, hybrid fern. It is formed by the crossing of lobed spleenwort (
''A. pinnatifidum'') with ebony spleenwort (
''A. platyneuron''). Found intermittently where the parent species grow together in the eastern United States, it typically grows on
sandstone
Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
cliffs, but is known from other substrates as well.
Description
''Asplenium'' × ''kentuckiense'' is a small fern, whose fronds grow in upright, spreading tufts. The stem is a shiny dark brown, the color extending well into the leaf blade. The blades are cut into pinnae near the base, which diminish into lobes in the upper part and eventually to teeth on the sides of a long, drawn-out tip. The fronds are
dimorphic, with the fertile fronds much longer and of a different shape than the sterile fronds.
The fronds of ''A.'' × ''kentuckiense'', which are long, are closely spaced along a
rhizome
In botany and dendrology, a rhizome ( ) is a modified subterranean plant stem that sends out roots and Shoot (botany), shoots from its Node (botany), nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from ...
in diameter. The
stipe (the stalk of the leaf, below the blade) is shiny and brown to black.
The overall shape of the blade is oblong, drawn out at length at the tip. It is cut into four to six pairs of pinnae near the base, which diminish to lobes further above, and then merely to teeth in the long tip. The pinnae are stalked, more or less lack teeth, and are typically long and wide at the base. The lower pinnae have a distinct lobe or
auricle pointing toward the blade tip. The dark color of the stipe extends some distance into the
rachis
In biology, a rachis (from the [], "backbone, spine") is a main axis or "shaft".
In zoology and microbiology
In vertebrates, ''rachis'' can refer to the series of articulated vertebrae, which encase the spinal cord. In this case the ''rachi ...
(leaf axis), the rest of which is flat and green. The leaf tissue has a somewhat papery texture.
Dark brown
spore
In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
s (none of which are viable) are plentiful in
sori covering the backs of the pinnae in fertile fronds. Sterile fronds are somewhat blunt-tipped and triangular in shaped, lying nearly horizontal. The fertile fronds are about ten times longer, lanceolate with long-pointed tips, and stand erect. In this last character, ''A.'' × ''kentuckiense'' resembles its parent ''A. platyneuron''. The sporophyte has a chromosome number of 108.
''Asplenium'' × ''kentuckiense'' can potentially be confused with a number of the other
''Asplenium'' hybrids in the Appalachian ''Asplenium'' complex. It differs from Trudell's spleenwort (
''A.'' × ''trudellii''), another descendant of ''A. pinnatifidum'', by having a blade broadest at the middle or between the middle and the base, rather than at the base itself, and by the presence of brown color throughout the stipe and sometimes into the rachis. ''A.'' × ''trudellii'' also has a slightly thicker texture, lighter brown spores, and two to three stalked and toothed pinnae at the base. In contrast to Boydston's spleenwort (
''A.'' × ''boydstoniae''), ''A.'' × ''kentuckiense'' has fewer than fifteen pairs of pinnae, which are not
sessile, and when dark color is present in the rachis, it covers less than seven-eights of that structure. The most similar hybrid to ''A.'' × ''kentuckiense'' is probably Graves' spleenwort (
''A.'' × ''gravesii''), a hybrid of ''A. pinnatifidum'' and Bradley's spleenwort (
''A. bradleyi''). In ''A.'' × ''kentuckiense'', the blade tapers at the base, the second and third pairs of pinnae being shorter than the fourth and fifth; in ''A.'' × ''gravesii'', all these pairs are approximately equal inside. ''A.'' × ''kentuckiense'' takes on a somewhat papery textures when dried, while ''A.'' × ''gravesii'' is more leathery. Finally, the
guard cells
Guard cells are specialized cells in the epidermis of leaves, stems and other organs of land plants that are used to control gas exchange. They are produced in pairs with a gap between them that forms a stomatal pore. The stomatal pores are larg ...
of the latter average 49 micrometers, slightly larger than the 46 micrometers of the former. As this character can only be examined by microscope, and the ranges of individual guard cell size overlap, some care is required in its use; 30 measurements from a single pinna were used to obtain an average length in previous studies. It is particularly useful in determining the identity of dried material.
Taxonomy
The species was first described by Thomas N. McCoy, based on a type specimen collected in 1934 at Keyser Creek,
Boyd County, Kentucky
Boyd County is a County (United States), county located in the Commonwealth (U.S. state), U.S. Commonwealth of Kentucky. As of the 2020 United States census, 2020 census, its population was 48,261. The county seat is Catlettsburg, Kentucky, Cat ...
. Other specimens were collected in
Calloway County and
Rowan County. Its separation from other ''Asplenium'' hybrids was done on the advice of
Edgar T. Wherry, who identified it as a probable hybrid between ''A. pinnatifidum'' and ''A. platyneuron'', on the basis of morphology and its occurrence at sites where both parent species were found. The earliest collection made of the species was probably that of
Franklin Sumner Earle
Franklin Sumner Earle (September 4, 1856 – January 31, 1929) was an American mycologist who specialized in fungal plant diseases. He was the first ever mycologist to be employed at the New York Botanical Garden, and was the author of ''The Gene ...
, around 1880, who identified it as ''A. pinnatifidum''.
In 1954,
Herb Wagner
Warren Herbert Wagner Jr. (August 29, 1920 – January 8, 2000) was an eminent American botanist who was trained at Berkeley with E.B. Copeland and lived most of his professional career in Michigan.
History
Wagner was instructed in the ways o ...
, who did not yet have access to live material, noted that the size of the
guard cell
Guard cells are specialized cells in the epidermis of leaves, stems and other organs of land plants that are used to control gas exchange. They are produced in pairs with a gap between them that forms a stomatal pore. The stomatal pores are lar ...
s in ''A.'' × ''kentuckiense'' suggested that it was
triploid
Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...
, consistent with its proposed parentage. He also noted that, in theory, the crossing of mountain spleenwort (''A. montanum'') with Tutwiler's spleenwort (''A. tutwilerae'') or of ''A. bradleyi'' with walking fern (''A. rhizophyllum'') could also produce ''A.'' × ''kentuckiense''. Smith, Bryant, and Tate obtained live material in 1961, which allowed them to observe that the species is indeed triploid, and that no pairing of
homologous chromosome
Homologous chromosomes or homologs are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during meiosis. Homologs have the same genes in the same locus (genetics), loci, where they provide points along e ...
s occurred during
meiosis
Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...
. This strongly supported the hypothesis that ''A.'' × ''kentuckiense'' developed from the crossing of ''A. pinnatifidum'' and ''A. platyneuron'', as the former species is not descended from ''A. platyneuron''.
Chromatographic experiments reported in 1963 showed that, like ''A.'' × ''gravesii'', chromatograms made from ''A.'' × ''kentuckiense'' contained all the compounds from the chromatograms of all three of its diploid ancestors: ''A. montanum'', ''A. platyneuron'', and ''A. rhizophyllum''.
In 1974,
John Mickel John Mickel may refer to:
* John Mickel (racing driver) (b. 1971)
* John Mickel (politician) (b. 1953)
* John Mickel (rugby union)
* John T. Mickel (1934–2024), botanist
{{hndis, Mickel, John ...
published ''Asplenosorus kentuckiensis'' as a new combination for the species to allow the continued recognition of the genus ''Camptosorus'' for the walking ferns. Since then, phylogenetic studies have shown that ''Camptosorus'' nests within ''Asplenium'', and current treatments do not recognize it as a separate genus.
Distribution and habitat
''Asplenium × kentuckiense'' has a scattered, patchy distribution in the
Appalachian Mountains
The Appalachian Mountains, often called the Appalachians, are a mountain range in eastern to northeastern North America. The term "Appalachian" refers to several different regions associated with the mountain range, and its surrounding terrain ...
,
Shawnee Hills, and
Ozarks
The Ozarks, also known as the Ozark Mountains, Ozark Highlands or Ozark Plateau, is a physiographic region in the U.S. states of Missouri, Arkansas, and Oklahoma, as well as a small area in the southeastern corner of Kansas. The Ozarks cover ...
. It has been reported from Virginia, West Virginia,
Pike County, Ohio
Pike County is a county located in the Appalachian (southern) region of the U.S. state of Ohio. As of the 2020 census, the population was 27,088. Its county seat is Waverly, and the county is named for explorer Zebulon Pike.
History
Pike Co ...
, Kentucky,
Perry County, Indiana
Perry County is a County (United States), county located in the Southwestern Indiana, southwestern part of the U.S. state of Indiana. As of 2020, the population was 19,170. The county seat is Tell City, Indiana, Tell City. It is the hilliest co ...
,
Union County, Illinois
Union County is a county located in the U.S. state of Illinois. According to the 2020 United States census, it had a population of 17,244. Its county seat is Jonesboro. It is located in the southern portion of Illinois known locally as " Litt ...
and Georgia. An outlying station in
Benton County, Arkansas
Benton County is a county in the Northwest region of the U.S. state of Arkansas. Created as Arkansas' 35th county on September 30, 1836, Benton County contains thirteen incorporated municipalities, including Bentonville, the county seat, and ...
has been extirpated.
Specimens of ''A.'' × ''kentuckiense'' have largely been reported from sandstone cliffs. One specimen from
Pittsylvania County, Virginia
Pittsylvania County is a county located in the Commonwealth of Virginia, United States. At the 2020 census, the population was 60,501. The county seat is Chatham.
Pittsylvania County is included in the Danville, VA Micropolitan Statistical ...
, originally identified as ''A.'' × ''gravesii'', was found on a boulder in open woods, probably
quartzite
Quartzite is a hard, non- foliated metamorphic rock that was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tecton ...
. At one site near
Toccoa, Georgia, a few specimens were found growing on granitic
gneiss
Gneiss (pronounced ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under p ...
, rather than sandstone or quartzite. Herb Wagner suggested searching for it in disturbed areas where soil-growing ''A. platyneuron'' and rock-growing ''A. pinnatifidum'' might mingle.
See also
*
Asplenium hybrids
Notes and references
Notes
References
Works cited
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External links
NatureServe ExplorerLectotype of the species(McCoy's collection from Calloway County)
{{DEFAULTSORT:Asplenium kentuckiense
kentuckiense
Plant nothospecies
Plants described in 1936
Ferns of the United States
Endemic flora of the United States
Flora of the Eastern United States