Penstemon kralii
Penstemon kralii, commonly known as Kral's beardtongue, is a rare species of flowering plant in the family Plantaginaceae. It is a perennial herb endemic to the southwestern escarpment of the Cumberland Plateau in northeastern Alabama and southeastern Tennessee. The species occurs primarily along the edges of dry, calcareous juniper–oak–hickory woodlands developed over Mississippian-aged limestone.
The species was formally described by American botanist Dwayne Estes in 2012. Its specific epithet honors botanist Robert Kral, who collected an unidentified specimen of the species in Alabama in 1970.
Description
Penstemon kralii is a perennial herb growing from a short, persistent stem base or caudex. It produces one or several erect to ascending stems. The stems are usually unbranched below the inflorescence and are covered with short, non-glandular hairs. Near the inflorescence, these are gradually replaced by longer glandular hairs.
The leaves are simple, opposite, and arranged in pairs at right angles to the pairs above and below them. The middle stem leaves are generally the largest. They are lance-shaped to oblong, dark green, and have sharply serrated margins. The leaf bases are rounded to somewhat heart-shaped and partly clasp the stem.
The terminal inflorescence is a thyrse. The flowers are slightly nodding. Each flower has a pale lavender to nearly white, bilaterally symmetrical corolla. The interior of the corolla usually bears conspicuous dark purple nectar-guide lines and two prominent ridges along the floor of the throat. The lower three corolla lobes project beyond the upper two.
The fertile stamens remain within the corolla. The sterile fifth stamen, or staminode, is slightly exserted and densely covered near its tip with golden-brown hairs, producing the “bearded” appearance characteristic of the genus. The fruits are broadly egg-shaped capsules.
Flowering generally occurs from May through June.
Taxonomy
Penstemon kralii was described by Dwayne Estes in 2012 in the Journal of the Botanical Research Institute of Texas. The holotype was collected near the eastern base of Keel Mountain in Jackson County, Alabama.
Herbarium specimens of the species had previously been confused with other southeastern beardtongues, especially Penstemon laevigatus, Penstemon smallii, and Penstemon tenuis. During work on the Flora of Tennessee, Estes examined unusual specimens from northeastern Alabama that did not conform to any recognized species. Further study determined that they represented an undescribed taxon.
The species belongs to a group of southeastern beardtongues characterized by pubescent stems, strongly two-ridged corolla throats, and lower corolla lobes that extend beyond the upper lobes. It is distinguished from P. smallii by its much smaller flowers. It differs from P. tenuis in having broader leaves, paler and more prominently lined flowers, linear-attenuate sepals, and a dry calcareous upland habitat rather than wetlands.
The specific name kralii honors Robert Kral, a botanist noted for his research on the flora and rare plants of the southeastern United States. Kral collected the species in Morgan County, Alabama, in 1970 but provisionally identified the specimen as P. laevigatus with a question mark.
Distribution and habitat
Penstemon kralii is restricted to the southwestern Cumberland Plateau escarpment of northeastern Alabama and southeastern Tennessee. It has been documented in Blount, Jackson, Madison, Marshall, and Morgan counties in Alabama and in Franklin County, Tennessee.
The species grows principally along forest edges in dry to mesic, calcareous juniper–oak–hickory woodlands over Mississippian limestone. Typical canopy trees include chinkapin oak, Shumard oak, shagbark hickory, white ash, eastern red cedar, winged elm, and American smoketree.
Associated shrubs and small trees include eastern redbud, Viburnum rufidulum, Sideroxylon lycioides, Hypericum frondosum, and Forestiera ligustrina. Associated herbaceous plants reported in the original description include Camassia scilloides, Clematis glaucophylla, Silphium brachiatum, Solidago auriculata, and Spigelia marilandica.
Collection history
The earliest known herbarium specimen of Penstemon kralii was collected near Huntsville, Alabama, in 1896. Roland McMillan Harper collected another specimen in Blount County in 1938, which was later tentatively annotated as P. laevigatus. Robert Kral collected the plant in Morgan County in 1970 and likewise questioned whether it belonged to P. laevigatus.
Additional Alabama specimens were collected during the later 20th century, but the plant remained unrecognized as a distinct species. The first confirmed Tennessee collections were made in Franklin County during the research that led to its formal description.
Conservation
NatureServe classifies Penstemon kralii as globally imperiled, with a conservation rank of G2. It is ranked N2 nationally in the United States and S1, or critically imperiled, in both Alabama and Tennessee. It is not currently listed under the United States Endangered Species Act.
NatureServe recognizes approximately twelve occurrences across its range. All known populations are reportedly small, although the total number of individual plants is unknown.
Potential threats include residential or commercial development, suppression of natural fire regimes, recreational-trail construction and use, and roadside or utility right-of-way maintenance. Many populations occur along roadsides or trail edges, where they may be affected by herbicide use, soil erosion, mowing, and encroachment by woody vegetation.
Recommended conservation measures include monitoring known populations, surveying suitable limestone habitat for additional occurrences, documenting population abundance and reproductive success, identifying the most serious threats, and evaluating long-term protection and management of high-quality sites.
References
kralii Category:Flora of Alabama Category:Flora of Tennessee Category:Plants described in 2012