Astragalus osterhoutii is a rare species of milkvetch

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 name Osterhout milkvetch. It is endemic to Grand County, Colorado

Grand County, Colorado

Grand County is the 21st largest of the 64 counties of the State of Colorado of the United States. The county population was 12,442 at U.S. Census 2000...

, where it is known from a few populations in Middle Park

Middle Park (Colorado basin)

Middle Park is a high basin in the Rocky Mountains of north-central Colorado in the United States. It is located in Grand County, on the southwest slope of Rocky Mountain National Park, approximately 50 miles west of Boulder.-Description:The basin surrounds the headwaters of the Colorado River...

, a mountain basin. There are five or six occurrences. It 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...

.

The plant grows on sagebrush

Sagebrush

Sagebrush is a common name of a number of shrubby plant species in the genus Artemisia native to western North America;Or, the sagebrush steppe ecoregion, having one or more kinds of sagebrush, bunchgrasses and others;...

 badlands

Badlands

A badlands is a type of dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded by wind and water. It can resemble malpaís, a terrain of volcanic rock. Canyons, ravines, gullies, hoodoos and other such geological forms are common in badlands. They are often...

 on soils originating from the Niobrara Formation

Niobrara Formation

The Niobrara Formation, also called the Niobrara Chalk , is a geologic formation in North America that was laid down between 87 and 82 million years ago during the Coniacian, Santonian, and Campanian ages of the Late Cretaceous. It is composed of two structural units, the Smoky Hill Chalk Member...

 and the Pierre Shale

Pierre Shale

The Pierre Shale is a geologic formation or series in the Upper Cretaceous which occurs east of the Rocky Mountains in the Great Plains, from North Dakota to New Mexico....

. The gray-brown shale

Shale

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

 and siltstone

Siltstone

Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...

 clay soils are high in selenium

Selenium

Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

, which the plant concentrates, causing it to develop a foul odor.

This is a perennial herb producing many slender, erect, green stems up to a meter tall. The leaves are made up of several narrow linear leaflets up to 3 centimeters long. The 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...

 bears cream-colored, pealike flowers each over 2 centimeters long. The fruit is a flattened legume pod up to 4 centimeters long.

Threats to the species include flooding and reservoir

Reservoir

A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...

 creation, which have eliminated at least one occurrence. All-terrain vehicle

All-terrain vehicle

An all-terrain vehicle , also known as a quad, quad bike, three wheeler, or four wheeler, is defined by the American National Standards Institute as a vehicle that travels on low pressure tires, with a seat that is straddled by the operator, along with handlebars for steering control...

 use and oil and gas exploration activities damage the habitat occupied by the plant.