Boechera Species, Braun's Rock Cress, Nevada Rockcress

THIS PLANT IS ENDANGERED!

Both varieties of Arabis perstellata E.L. Braun, (Arabis perstellata E. L. Braun var. ampla Roll...Read Moreins, large rock cress, and Arabis perstellata E.L. Braun var. perstellata Fernald, small rock cress) are perennial members of the mustard family (Brassicaceae). The large rock cress is known from only one county in Tennessee, and the small rock cress is known from only three counties in Kentucky. 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 new flowering 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 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 survive in full shade or filtered light, but are not found in full sunlight (Jones 1991).