''Arabis macdonaldiana'' is a species of flowering plant in the
mustard family
Brassicaceae () or (the older) Cruciferae () is a medium-sized and economically important family of flowering plants commonly known as the mustards, the crucifers, or the cabbage family. Most are herbaceous plants, while some are shrubs. The le ...
known by the common name MacDonald's rockcress. It is native to northern
California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
and
Oregon
Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...
, where it grows on newly exposed, barren
serpentine soil
Serpentine soil is an uncommon soil type produced by weathered ultramafic rock such as peridotite and its metamorphic derivatives such as serpentinite. More precisely, serpentine soil contains minerals of the serpentine subgroup, especially anti ...
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 is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic via ...
, particularly of
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...
, which is one of several metals plentiful in the serpentine.
[Center for Plant Conservation]
On September 29, 1978, this was the second plant to be federally listed as an
endangered species
An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...
.
[
]
Description
This is a perennial herb growing one or more slender stems from a small, branching caudex
A caudex (plural: caudices) of a plant is a stem, but the term is also used to mean a rootstock and particularly a basal stem structure from which new growth arises.pages 456 and 695
In the strict sense of the term, meaning a stem, "caudex" is m ...
, 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
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. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed o ...
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.
See also
* List of ''Arabis'' species
References
External links
Jepson Manual TreatmentUSDA Plants ProfileThe Nature ConservancyPhoto gallery
macdonaldiana
Flora of Oregon
Plants described in 1903
NatureServe imperiled species
{{Brassicales-stub