Arabis macdonaldiana
Encyclopedia
Arabis macdonaldiana is a species of flowering plant in the mustard family
known by the common name MacDonald's rockcress. It is native to northern California
and Oregon
, where it grows on newly exposed, barren serpentine soil
s in openings in temperate coniferous forest habitat. It is a rare and endangered plant known from several sites in California and approximately two occurrences in Oregon, where it is threatened mainly by mining
, particularly of nickel
, which is one of several metals plentiful in the serpentine. On September 29, 1978, this was the second plant to be federally listed as an endangered species
.
This is a perennial herb growing one or more slender stems from a small, branching caudex
, reaching 10 to 30 centimeters tall. There is a basal patch of leaves with edges lined in small, widely spaced teeth which are sometimes tipped with spines. The leaves may lack teeth and have wavy margins. There may also be a few smaller leaves along the stem. The top of the stem forms an inflorescence
of a few flowers, each with four bright rose-purple petals. The fruit is a flat, straight silique
about 3 centimeters long which contains several oblong little seeds.
Brassicaceae
Brassicaceae, a medium sized and economically important family of flowering plants , are informally known as the mustards, mustard flowers, the crucifers or the cabbage family....
known by the common name MacDonald's rockcress. It is native to northern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
and Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
, where it grows on newly exposed, barren serpentine soil
Serpentine soil
A serpentine soil is derived from ultramafic rocks, in particular serpentinite, a rock formed by the hydration and metamorphic transformation of ultramafic rock from the Earth's mantle....
s in openings in temperate coniferous forest habitat. It is a rare and endangered plant known from several sites in California and approximately two occurrences in Oregon, where it is threatened mainly by mining
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
, particularly of nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
, which is one of several metals plentiful in the serpentine. On September 29, 1978, this was the second plant to be federally listed as an endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
.
This is a perennial herb growing one or more slender stems from a small, branching caudex
Caudex
A caudex is a form of stem morphology appearing as a thickened, short, perennial stem that is either underground or near ground level . It may be swollen for the purpose of water storage, especially in xerophytes...
, reaching 10 to 30 centimeters tall. There is a basal patch of leaves with edges lined in small, widely spaced teeth which are sometimes tipped with spines. The leaves may lack teeth and have wavy margins. There may also be a few smaller leaves along the stem. The top of the stem forms an inflorescence
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
of a few flowers, each with four bright rose-purple petals. The fruit is a flat, straight silique
Silique
A silique or siliqua is a fruit of 2 fused carpels with the length being more than three times the width. The outer walls of the ovary usually separate when ripe, leaving a persistent partition...
about 3 centimeters long which contains several oblong little seeds.