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Plant Profile

Whited's Milkvetch (Astragalus sinuatus)

A close-up view of the white flowers of Astragalus sinuatus and the dry soil that it inhabits. Photo Credit: Washington NHP

Global Rank: G1 - Critically Imperiled
Legal Status: N/A
Family: Fabaceae
State: WA
Nature Serve ID: 133554
Lifeform: Forb/herb
Date Inducted in National Collection: 04/04/1991

Description:

Astragalus sinuatus is found only within a ten square mile (26 sq. km) area in Central Washington. Although much of the historic range of this species has been converted or destroyed by agriculture and grazing, there is quite a bit of suitable habitat remaining. Scientists do not know why A. sinuatus has not spread to these areas of seemingly suitable habitat. Whited's milkvetch presents quite a challenge to researchers and seed conservationists. The seed pods of this species are small and incredibly tough. It may take a pair of pliers to crack the fruit open and extract the seed. For all the work involved, the pods have only one or two (rarely more) seeds inside (and sometimes they are completely empty). In the wild, pods open at one end, releasing seeds as they shake in the wind or roll down the hill. Often, the pods are so tough that they do not open until weathered and rolled along the ground. Despite the tough pod, the seeds often fall victim to seed predation or larval damage. Certain insects can bore a tiny hole through the pod and the seed coat and deposit an egg within the seed. As the larvae develops it consumes the contents of the seed.

Where is Whited's Milkvetch (Astragalus sinuatus) located in the wild?

Habitat:

Astragalus sinuatus grows on rocky in the sagebrush/bunchgrass shrub steppe community. Associated species commonly include Lupinus sulphureus, Erigeron linearis, Phlox longifolia, Woodsia oregana, Balsamorhiza sagittata, Lomatium dissectum, Lithophragma bulberifera and Astragalus purshii. Astragalus sinuatus grows on southwest to southeast facing slopes which makes them warmer and drier than the reported temperatures. The region is very harsh and dry with reported winter lows around 20F (-6.6C) and summer highs around 87F (30.5C). Precipitation averages only 9 inches (22.9 cm) per year, most of which falls from October to June (fall to spring).

Distribution:

WA: EC (Eastern Cascades)

States & Provinces:

Whited's Milkvetch can be found in Washington

Which CPC Partners conserve Whited's Milkvetch (Astragalus sinuatus)?

University Of Washington Botanic Gardens

Conservation Actions

08/27/2020

Collect and store seeds from all known populations. Determine optimum germination procedures. Determine propagation and reintroduction protocols.

08/27/2020

Germination trials at the Berry Botanic Garden revealed that 8 weeks of cold stratification, followed by either a constant 68F (20C) or alternating 50/68F (10/20C) temperature yielded slightly higher germination rates (67%) than the same temperature treatments with no cold stratification (40% at 68F and 50% at 50/68F) (BBG file).

08/27/2020

Seed from one population is stored at The Berry Botanic Garden

Nature Serve Biotics

05/02/2017

Very narrowly endemic to a small creek drainage along the western edge of the Columbia Basin in central Washington. The species' habitat is threatened by fire suppression, fire management, non-native species invasions, grazing, and agricultural development.

Edward Guerrant, Ph.D.

01/01/2010

Years of fire suppression has lead to increased vegetative cover. Now, in the event that a fire does start, this increased fuel load will lead to hotter burning fires, which can kill native vegetation. (WNHP 1999). Invasion by weedy annual species (WNH

Edward Guerrant, Ph.D.

01/01/2010

As of 1995: 8 populations (one with 2 sub-populations) all in an area less than 10 square miles. Populations range in size from 5 to 2,900 individuals and from acre to 80 acres. The total population in 1994 was approximately 5,000 (Gamon 1995).

Edward Guerrant, Ph.D.

01/01/2010

Edward Guerrant, Ph.D.

01/01/2010

All populations have been subject to grazing by domestic livestock, especially cattle and horses, at some point since at least 1900, possibly as early at the 1880's (Gamon 1995). One population is within a ""Natural Area Preserve"" managed by the Washington Department of Natural Resources (Gamon 1995). The area is fenced to exclude livestock. A portion of another population on BLM land is designated as an ACEC (Area of Critical Environmental Concern). There is a grazing lease on the land, although the lessee has not grazed livestock there since around 1985 (Gamon 1995). All other sites are used periodically as range land for livestock (Gamon 1995) Seed from one population is stored at The Berry Botanic Garden

Edward Guerrant, Ph.D.

01/01/2010

Research ways to reduce big sagebrush cover other than fire that benefit Astragalus sinuatus (WNHP 1999). Determine why individuals appear to reproduce successfully, yet seemingly suitable habitat remains unoccupied (WNHP 1999). Determine factors influencing limited distribution.

Edward Guerrant, Ph.D.

01/01/2010

Collect and store seeds from all known populations. Determine optimum germination procedures. Determine propagation and reintroduction protocols.