Astragalus alpinus is a species of flowering plant in the legume family

Fabaceae

The Fabaceae or Leguminosae, commonly known as the legume, pea, or bean family, is a large and economically important family of flowering plants. The group is the third largest land plant family, behind only the Orchidaceae and Asteraceae, with 730 genera and over 19,400 species...

 known by the common name alpine milkvetch. It has a circumpolar

Arctic Circle

The Arctic Circle is one of the five major circles of latitude that mark maps of the Earth. For Epoch 2011, it is the parallel of latitude that runs north of the Equator....

 distribution, occurring throughout the upper latitude

Latitude

In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

s of the Northern Hemisphere. It is widespread in Eurasia. In North America it occurs from Alaska

Alaska

Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

 to Newfoundland

Newfoundland and Labrador

Newfoundland and Labrador is the easternmost province of Canada. Situated in the country's Atlantic region, it incorporates the island of Newfoundland and mainland Labrador with a combined area of . As of April 2011, the province's estimated population is 508,400...

 and as far south as Nevada

Nevada

Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...

 and New Mexico

New Mexico

New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...

.

This plant is variable in appearance. In general, it is a perennial herb growing from a taproot

Taproot

A taproot is an enlarged, somewhat straight to tapering plant root that grows vertically downward. It forms a center from which other roots sprout laterally.Plants with taproots are difficult to transplant...

 and rhizome

Rhizome

In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

 network topped with an underground 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...

. The roots have nitrogen-fixing

Nitrogen fixation

Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...

 nodules. The aboveground stems are up to 30 centimeters long and are mostly decumbent, forming a mat. The leaves are up to 15 centimeters long and are made up of several pairs of leaflets each up to 2 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...

 is a raceme of up to 30 flowers each about a centimeter long. The flowers are purple or blue. The fruit is a legume pod up to 1.7 centimeters long which contains seeds.

This plant grows in subalpine

Subalpine

The subalpine zone is the biotic zone immediately below tree line around the world. Species that occur in this zone depend on the location of the zone on the Earth, for example, Snow Gum in Australia, or Subalpine Larch, Mountain Hemlock and Subalpine Fir in western North America.Trees in the...

 and alpine climate

Alpine climate

Alpine climate is the average weather for a region above the tree line. This climate is also referred to as mountain climate or highland climate....

s, often in moist areas, such as woodlands and meadows around streams and lakes. It also occurs on tundra

Tundra

In physical geography, tundra is a biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word tūndâr "uplands," "treeless mountain tract." There are three types of tundra: Arctic tundra, alpine...

 and other cold, dry, exposed areas. It occurs on gravel bars and scree

Scree

Scree, also called talus, is a term given to an accumulation of broken rock fragments at the base of crags, mountain cliffs, or valley shoulders. Landforms associated with these materials are sometimes called scree slopes or talus piles...

. It is sometimes a pioneer species

Pioneer species

Pioneer species are species which colonize previously uncolonized land, usually leading to ecological succession. They are the first organisms to start the chain of events leading to a livable biosphere or ecosystem...

, colonizing land in the primary phase

Primary succession

Primary succession is one of two types of biological and ecological succession of plant life, occurring in an environment in which new substrate devoid of vegetation and usually lacking soil, such as a lava flow or area left from retreated glacier, is deposited...

 of ecological succession

Ecological succession

Ecological succession, is the phenomenon or process by which a community progressively transforms itself until a stable community is formed. It is a fundamental concept in ecology, and refers to more or less predictable and orderly changes in the composition or structure of an ecological community...

, such as roads and bare land turned over during frost heave. It has been observed regrowing early in recently burned areas in Grand Teton National Park

Grand Teton National Park

Grand Teton National Park is a United States National Park located in northwestern Wyoming, U.S. The Park consists of approximately and includes the major peaks of the long Teton Range as well as most of the northern sections of the valley known as Jackson Hole. Only south of Yellowstone...

. It also grows in vegetated areas. Plants occurring in harsh conditions are smaller than those in more favorable sites.

This plant species provides food for caribou, arctic hare

Arctic Hare

The arctic hare , or polar rabbit is a species of hare which is adapted largely to polar and mountainous habitats. The arctic hare survives with a thick coat of fur and usually digs holes under the ground or snow to keep warm and sleep...

s, Greater Snow Geese

Snow Goose

The Snow Goose , also known as the Blue Goose, is a North American species of goose. Its name derives from the typically white plumage. The genus of this bird is disputed...

, and grizzly bear

Grizzly Bear

The grizzly bear , also known as the silvertip bear, the grizzly, or the North American brown bear, is a subspecies of brown bear that generally lives in the uplands of western North America...

s.

This species may be divided into two varieties, var. alpinus occurring in the Arctic and var. brunetianus occurring in northeastern North America at lower latitudes.