Astragalus cremnophylax
Encyclopedia
Astragalus cremnophylax is a rare species of milkvetch
known by the common names sentry milkvetch and cliff milkvetch. It is endemic to Arizona
, where the three varieties grow in three separate locations. The rarest variety, var. cremnophylax, is a federally listed endangered species
which grows only on the rim of the Grand Canyon
. The two other varieties are known from the Buckskin Mountains
and Marble Canyon
.
This plant is a resident of the Kaibab Limestone
, where it grows in cracks in the bare limestone
. The habitat is a pavement of dry, exposed, white rock that takes full sun and brisk, dry winds. Plants occur in rock crevices that have a few centimeters of soil, if any, and accumulate a minute amount of moisture at times. The species sometimes grows alongside Petrophytum caespitosum, which occupies a similar niche.
The rare var. cremnophylax was threatened with extinction when its tiny populations were trampled by tourists
creeping to the edge of the Grand Canyon. Fence
s have been placed at strategic locations there to protect the plant.
Astragalus
Astragalus is a large genus of about 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae, subfamily Faboideae. The genus is native to temperate regions of the Northern Hemisphere...
known by the common names sentry milkvetch and cliff milkvetch. It is endemic to Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
, where the three varieties grow in three separate locations. The rarest variety, var. cremnophylax, is a federally listed 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...
which grows only on the rim of the Grand Canyon
Grand Canyon
The Grand Canyon is a steep-sided canyon carved by the Colorado River in the United States in the state of Arizona. It is largely contained within the Grand Canyon National Park, the 15th national park in the United States...
. The two other varieties are known from the Buckskin Mountains
Buckskin Mountains
The Buckskin Mountains are a mountain range in western-central Arizona, USA. The range lies just east of the north-south Colorado River, and borders south of the east-west, west-flowing Bill Williams River....
and Marble Canyon
Marble Canyon
Marble Canyon is the section of the Colorado River canyon in northern Arizona from Lee's Ferry to the confluence with the Little Colorado River, which marks the beginning of the Grand Canyon....
.
This plant is a resident of the Kaibab Limestone
Kaibab Limestone
The Kaibab is a geologic formation that is spread across the U.S. states of northern Arizona, southern Utah, east central Nevada and southeast California. This geologic unit is part of the Park City Group in Nevada and Utah and is sometimes locally classified as a geologic group in Utah...
, where it grows in cracks in the bare limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
. The habitat is a pavement of dry, exposed, white rock that takes full sun and brisk, dry winds. Plants occur in rock crevices that have a few centimeters of soil, if any, and accumulate a minute amount of moisture at times. The species sometimes grows alongside Petrophytum caespitosum, which occupies a similar niche.
The rare var. cremnophylax was threatened with extinction when its tiny populations were trampled by tourists
Tourism
Tourism is travel for recreational, leisure or business purposes. The World Tourism Organization defines tourists as people "traveling to and staying in places outside their usual environment for not more than one consecutive year for leisure, business and other purposes".Tourism has become a...
creeping to the edge of the Grand Canyon. Fence
Fence
A fence is a freestanding structure designed to restrict or prevent movement across a boundary. It is generally distinguished from a wall by the lightness of its construction: a wall is usually restricted to such barriers made from solid brick or concrete, blocking vision as well as passage .Fences...
s have been placed at strategic locations there to protect the plant.
Varieties
There are three varieties of this species:- A. cremnophylax var. cremnophylax - Grand Canyon
- A. cremnophylax var. myriorrhaphis - Buckskin Mountains
- A. cremnophylax var. hevronii - Marble Canyon