Species Fact Sheet McDonald's rockcress Arabis macdonaldiana
STATUS: ENDANGERED CRITICAL HABITAT: NONE
McDonald's rockcress potentially occurs in these Oregon counties: Curry, Josephine (Map may reflect historical as well as recent sightings)
McDonald's rock-cress was federally listed as endangered without
critical habitat in 1978. A recovery plan was published for the
California populations in 1990.
Historical Status and
McDonald's rock-cress is one of several closely related endemic
species (species restricted to a well-defined geographic area)
which have evolved in the Siskiyou Mountains region of southwest
Oregon and northwest California. This species was not discovered
in Oregon until 1980. It is an attractive plant, as are many
of the endemic rock-cress species of the Siskiyou Mountains.
Taxonomic studies are currently under way to investigate the
relationship of the Oregon population to those in California.
Description and Life
McDonald's rock-cress is s perennial species in the mustard
family (Brassicaceae). This species has a branched caudex (short,
vertical, often woody stem at or just beneath the ground surface)
and several simple stems that measure 5 to 20 centimeters (2
to 8 inches) in height. The lower leaves are in rosettes (a cluster
of leaves in a circle), are spatulate (rounded above and narrowed
to the base), measure 1 to 2 centimeters (0.4 to 0.8 inches)
long and 4 to 7 millimeters (0.2 to 0.3 inches) wide, are toothed,
and are essentially smooth. The petals are rose or purple in
color and measure 9 to 11 millimeters (0.35 to 0.43 inches) long.
The fruits are siliques (elongate, dry, and open at maturity)
that measure 3 to 4 centimeters (1.2 to 1.6 inches) long. Flowering
typically occurs from late April through June.
This species is distinguished from other rock-cress species
by being almost glabrous (without hairs or glands) and by possessing
spatulate basal leaves 1 to 2 centimeters (0.4 to 0.8 inches)
McDonald's rock-cress occurs on serpentine soils (high in magnesium,
iron, and certain toxic metals). This species is found below
1500 meters (4920 feet) elevation in dry, open woods or brushy
slopes, with sanicles (Sanicula spp.), violets (Viola spp.),
and onions (Alium spp.).
Reasons for Decline
Mining activities and collection of specimens has
contributed to the decline of this species.
This species is currently cnsidered to be restricted to Curry
and Josephine Counties in southwest Oregon on USDA Forest Service
land and private land, and in adjacent Del Norte County, California.
It has also been reported from Mendocino County, California.