Rockcresses are mostly slender biennial to perennial herbs, occasionally somewhat woody, sometimes hairless but commonly sparsely to densely short-hairy, the hairs simple, T-shaped (attached near their middle) or star-shaped, non-glandular. The plants have 1 to several stems from a simple to branched base, with several basal leaves that are stalked and arranged in a rosette, entire to pinnately lobed with the end lobe the largest. The stem leaves are alternate, mostly stalkless, sometimes short-stalked, generally with backward, ear-like lobes at the base. The flowers are arranged in simple to branched, usually elongate and loose clusters without bracts. The 4 sepals are erect, hairless to hairy, greenish to purple, the outer 2 often slightly humped at base. The 4 petals are white to pink, red, or deep purple, obovate-spatulate. The fruit pods are linear, readily opening when ripe, straight to somewhat curved, erect to drooping, hairless to hairy, mostly 1-nerved to mid-length or above, strongly compressed to somewhat 4-sided, nearly or quite stalkless. Style is lacking or very short, the stigma entire to slightly 2-lobed. There are numerous seeds, in 1 to 2 series in each cell, rounded to oblong-oval, wingless or more commonly partially or wholly encircled by a membranous wing. The genus has one hundred or more species in desert to alpine habitats of the Northern Hemisphere. The name comes from the name of the country, Arabia. All rockcresses are edible, with the typical sharp flavor of plants of the mustard family. The tender leaves and flowers are usually added to salads and sandwiches for flavor, but some people like their hot horseradish flavor, and enjoy them alone.
Guide to Identify Presented Species of Genus Arabis
FLOWERS WHITE OR PURPLISH, PLANTS MOSTLY DENSELY HAIRY
A. holboellii Holboell's Rockcress 10-100 cm tall, with star-shaped hairs at least below. Flowers white-purple, bent down. Sepals hairy, 2.5-5 mm long. Leaves 1-5 cm long, 2-7 mm broad, w. short, star-shaped hairs. Slopes.