Cress, Braun's Rock

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Cress, Braun's rock

Arabis perstellata

division: Magnoliophyta

class: Magnoliopsida

order: Capparales

family: Brassicaceae

status: Endangered, ESA

range: USA (Kentucky, Tennessee)

Description and biology

Braun's rock cress is a member of the mustard family. There are two varieties of the species, the Arabis perstellata var. ampla, and Arabis perstellata var. perstellata. Braun's rock cress is a perennial (plant that lives, grows, flowers, and produces seeds for three or more consecutive years) that forms a low mat with gray foliage (leaves) and white-to-lavender flowers. There is downy hair on both its stem and its foliage. The plant's stem can grow to about 32 inches (80 centimeters) long. The plant produces a new cluster of leaves at its base annually. New branches grow from the leaf cluster produced the prior year. Lower leaves range in size from 1.6 to 6 inches (4 to 15 centimeters). Upper leaves measure only about 1.4 inches (3.5 centimeters). The flowers have four tiny petals and four pale green sepals (a kind of leaf at the base of the flower petals). Braun's rock cress produces flowers from late March to early May and mature fruits in mid-May to early June. Its

seeds are reddish brown and only about 0.04 inches (1 millimeter) long.

Habitat and current distribution

Braun's rock cress grows on moist, but not usually wet, rocky formations protruding from steep, wooded slopes. They also occur around the bases of trees. They live in full shade or filtered light.

One subspecies, the small rock cress (Arabis p. var. perstellata), occurs in 27 populations in Kentucky, mainly in Franklin County, but with a few in Owen and Henry Counties. The other subspecies, the large rock cress (Arabis p. var. ampla) is known to exist only in two populations in Rutherford County, Tennessee.

History and conservation measures

The surviving populations of Braun's rock cress are threatened by the destruction of their natural habitat, by the introduction of weeds that compete for their space, by livestock trampling them, by logging, and by construction. There are about 10 populations of the small rock cress that have not at this time been threatened by any of these conditions, but are likely to be threatened in the near future as development progresses. One of the two populations of the large rock cress consists of older plants, suggesting that the plants have not been reproducing.

The populations of Braun's rock cress in Kentucky occur on privately owned land. The Kentucky Nature Preserves Commission has worked with the landowners to try to protect the species within its natural habitat. In 2001, one of the landowners enrolled a 118-acre parcel of land—the natural habitat of Braun's rock cress—on the Kentucky Natural Areas Registry program, to be preserved as a natural area. While the private owners and the state have been striving to save the species, critics have claimed that the U.S. Fish and Wildlife Service (USFWS) has not fulfilled its obligations to the species under the Endangered Species Act (ESA). On November 8, 2001, a federal judge ordered the USFWS to designate critical habitat for 16 endangered species. One of these 16 endangered species was Braun's rock cress. Although the species had been designated as endangered, there had been no attempt to preserve habitat for it, as required under the ESA. In 2003, the USFWS responded to the court case, saying that designating critical habitat for endangered species as required by the ESA was slowing down its processes and distracting the agency from more important species protection.