The following Participating Institutions are custodians for this species in the CPC National Collection:
Rae Selling Berry Seed Bank & Plant Conservation Programs
University Of Washington Botanic Gardens
The conservation of Astragalus sinuatus is fully sponsored.
Edward Guerrant, Ph.D. contributed to this Plant Profile.
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.
Distribution & Occurrence
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).
|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).|
Conservation, Ecology & Research
Occasional fire (30-90 year interval) probably played a role historically in maintaining open habitat for this species. Now, fire may lead to increased success of weedy annuals (WNHP 1999). Other disturbances can also have a negative impact as they may increase the number of weedy species which may eventually out-compete A. sinuatus (Gamon 1995).
The plant actively grows for only a short period every year. Leaf emergence is most likely initiated in late March or early April. The plant is fully leafed-out by mid April, just when floral buds appear. Most flowers bloom between late April and early May, and the majority of fruits develop by mid-May. Seed is fully mature by the middle to end of July. Most leaves begin to senesce by June, and in summer, the only identifying features remaining may be the empty seedpods (Gamon 1995). Astragalus sinuatus is sensitive to fluctuating precipitation levels. During drought years, many plants remain dormant, never emerging from the ground. Those that do emerge may not flower (Gamon 1995).
Knowledge of the reproductive biology of Astragalus sinuatus is scant. It is believed that they are a predominantly out-crossing species, although some members of the genus Astragalus can self-pollinate as well. Bumblebees have been observed in and around the plant (Gamon 1995). The incredibly tough pods do not naturally split along the "seam" as a pea or a bean would. They open only at the end, and seeds may fall out by shaking in the wind or as the pod rolls downhill. Pods may open more as they are weathered and rolled along the ground. Seeds must be scarified (have their surface scratched slightly), before they will germinate. Most seeds are dispersed close to the parent plant or slightly downhill from it. A. sinuatus is more common lower on slopes (Gamon 1995).
Like other members of the Pea Family (Fabaceae), Astragalus sinuatus can develop a symbiotic relationship with nitrogen fixing bacteria that live in their roots. This gives them a competitive advantage over other species in nitrogen poor soils and increases the available nitrogen in the soil (Gamon 1995).
Cattle do not seem to eat Astragalus sinuatus plants. They do, however, compact the soil, accelerate soil erosion, and contribute to an increase in weedy, annual, non-native species, such as cheatgrass (Bromus tectorum) (Gamon 1995). Areas most heavily used by cattle have lower population densities and lower seedling recruitment than areas less heavily used by livestock.
Invasion by weedy annual species (WNH
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
Determine why individuals appear to reproduce successfully, yet seemingly suitable habitat remains unoccupied (WNHP 1999).
Determine factors influencing limited distribution.
Determine optimum germination procedures.
Determine propagation and reintroduction protocols.
WNHP. 1981. An illustrated guide to the endangered, threatened and sensitive vascular plants of Washington. Olympia: Washington Natural Heritage Program. 328p.