U.S. FISH AND WILDLIFE SERVICE
DIVISION OF ENDANGERED SPECIES

SPECIES ACCOUNTS

FAMILY: Brassicaceae

STATUS: Endangered, Federal Register, January 3, 1995

DESCRIPTION: Both varieties of Arabis perstellata E. L. Braun, (Arabis perstellata E. L. Braun var. ampla Rollins [large rock cress] and Arabis perstellata E. L. Braun var. perstellata Fernald [small rock cress]) are perennial members of the mustard family (Brassicaceae). Both varieties have round stems and alternate leaves. Their stems and foliage have a grayish coloration due to the large quantity of hairs. Their stems arise from horizontal bases and grow up to 80 centimeters (cm) (31.5 inches) long, often drooping from rock ledges. Each year a basal rosette of leaves is produced, and the new branches emerge from the old rosette of the previous season. Their lower leaves vary from 4 to 15 cm (1.6 to 6.0 inches) long and are obovate to oblanceolate with slightly toothed and pinnatifid margins. Their upper leaves are smaller - up to 3.5 cm (1.4 inches) long - and are elliptic to oblanceolate, with coarse teeth along the margin. Both surfaces of their leaves are stellate-pubescent. The inflorescence is an elongate raceme with numerous flowers. Their flowers have four petals that are 3 to 4 millimeters (mm) (0.12 to 0.16 inch) long, are white to lavender, and have four pale green sepals that are 2 to 3 mm (0.08 to 0.12 inch) long. There are six stamens, with two shorter than the other four. The ovary is elongate, two chambered, and develops into a silique. Fruiting stalks are about 1 cm (0.4 inch) long at maturity; siliques are up to 4 cm (1.6 inches) long and are covered with both simple and stellate hairs. Flowering is from late March to early May. Fruits mature from mid-May to early June. Their oblong seeds are reddish brown; somewhat flattened; about 1 mm (0.04 inch) long; and, in places, minutely hairy (Jones 1991).

Arabis perstellata was named by E. L. Braun from plants collected between 1936 and 1939 on wooded hillsides along Elkhorn Creek in Franklin County, Kentucky. Braun (1940) distinguished the new taxon from the similar Arabis dentata (Torr.) T. & G. (now called Arabis shortii [Fern.] Gleason) by its perennial habit; grayer, stellate pubescence of stems and leaves; and longer pedicels. Fernald (1946) treated A. shortii as a variety of A. perstellata, though it is now generally accepted that they represent two species (Kartesz and Kartesz 1980). In 1959, plants were discovered on steep limestone cliffs above the Stones River in Davidson County, Tennessee, by Dr. R. B. Channel. Rollins (1960) described these plants as Arabis perstellata var. ampla and distinguished them from the typical variety by their generally larger size, thinner and more entire leaves, and lesser pubescence. Rollins also reported the chromosome number of the Tennessee plants as n=7; the chromosome number of the Kentucky plants has yet to be determined.

RANGE AND POPULATION LEVEL: The two subspecies occupying distinct geographic areas. The small rock cress (Arabis p. var. perstellata) is currently known from 27 populations in Kentucky - 24 in Franklin County, 2 in Owen County, and 1 in Henry County. The large rock cress (Arabis p. var. ampla) is known from only two populations in Rutherford County, Tennessee.

The following information on Arabis p. var. ampla in Tennessee and Arabis p. var. perstellata in Kentucky is primarily from Jones (1991):

All known Arabis p. var. ampla populations in Tennessee are from the Cumberland River Subsection of the Central Basin Physiographic Region. Prior to the status survey conducted by Jones (1991), there were three records of large rock cress in Davidson County and two in Rutherford County. All three of the sites in Davidson County have been extirpated, and one of the sites in Rutherford County could not be relocated. One additional population was discovered in Rutherford County during the status survey. Of the two remaining populations, one is small - about 25 plants - and covers about 0.06 of an acre. The other population contains several hundred plants scattered over about 2.2 acres.

All known Arabis p. var. perstellata populations in Kentucky are from the Eden Shale Belt Subsection of the Blue Grass Physiographic Region. Prior to the status survey conducted by Jones (1991), there were three counties in Kentucky with occurrence records for the small rock cress - 1 in Henry County, 2 in Owen County, and 26 in Franklin County. One site in Owen County and seven sites in Franklin County have been extirpated. There was insufficient information to locate four other historic records (two in Franklin County and two from unknown counties). However, eight new populations were discovered during the status survey, and the 27 known small rock cress sites in Kentucky are distributed as follows: 1 population from Henry County, 2 populations from Owen County, and 24 populations from Franklin County. Of these 27 populations, 22 of them have fewer than 100 individual plants and 12 have 20 or fewer.

HABITAT: Arabis perstellata is typically found on wooded steep slopes with limestone outcrops. The outcrops tend to be moist but not wet; rarely, plants can be found on seepy outcrops. They also may be found in protected areas, such as around the bases of larger trees, or in areas where there is little competition, such as around areas regularly scoured by talus movement or erosion. The plants have a well-developed system of rootstocks that allow them to persist in these inhospitable sites. Sometimes plants display a weedy tendency, colonizing recent road cuts or animal paths through the woodlands. The plants exhibit shade/light requirements, surviving in full shade or filtered light, but are not found in full sunlight (Jones 1991).

The distribution of Arabis p. var. perstellata shows a strong correlation with the Kentucky River and its tributaries (primarily Elkhorn Creek), with most sites occurring in Franklin County. No sites have been found south of Frankfort along the Kentucky River, although appropriate habitat appears to be present. Arabis p. var. ampla is also associated with calcareous bluff habitat of a specific river - the Stones River. The two extant populations are somewhat atypical compared to historic sites because they occur on rocky knobs about 15 miles from the Stones River (Jones 1991).

REASONS FOR CURRENT STATUS: Arabis p. var. perstellata - Of the 27 known populations of small rock cress, 17 are threatened with destruction or adverse modification of their habitat. Eight are threatened by weedy competitors, four by weedy competitors and trampling, two by trampling, one by logging, and two by road work (one population was severely impacted by road work during the period the species was proposed for listing). The remaining 10 populations do not appear to have any immediate threats but are vulnerable to the aforementioned threats, as well as other habitat alterations, and potential inbreeding problems as neighboring populations decline. Active management is required to ensure that the species continues to survive at all sites.

Arabis p. var. ampla - Both remaining large rock cress populations in Tennessee are threatened from competition by weedy invaders and potentially by livestock grazing and trampling. Also, the smaller site appears to be comprised of older individuals, and there is little evidence of reproduction (Jones 1991). Additionally, Arabis p. var. ampla could be facing potential inbreeding problems because of low population numbers.

MANAGEMENT AND PROTECTION: To save the rock cress, all existing State and Federal legislation and regulations must be enforced (especially those related to the impacts of coal mining). All the Kentucky populations are privately owned. Three receive limited protection through their inclusion in State designated natural areas. Potential research and management needs include fencing areas, invasive species control, coordination with state Departments Of Transportation, and reintroduction and propagation techniques. The Kentucky Nature Preserves Commission is contacting all land owners and developing a management plan.

REFERENCES:

Braun, E. L. 1940. New plants from Kentucky. Rhodora 42:47-49.

Fernald, M. L. 1946. Identification and reidentifications of North American Plants. Rhodora 48:207-216.

Jones, R. L. 1991. Status Survey Report on Arabis perstellata var. perstellata. Unpublished report to the Asheville Field Office, U.S. Fish and Wildlife Service, Asheville, North Carolina. 94 pp.

Kartesz, J., and R. Kartesz. 1980. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. University of North Carolina Press, Chapel Hill, North Carolina.

Rollins, R. 1960. Arabis perstellata in Tennessee. Rhodora 62:242-244.

For more information please contact:

U.S. Fish and Wildlife Service
160 Zillicoa Street
Asheville, North Carolina 28801

Telephone: 704/258-3939 Ext. 229