Kingdom: Plantae

Phylum: Magnoliophyta -- flowering plants

Class: Magnoliopsida -- dicots

Family: Fabaceae -- pea

Common Name: Palouse milkvetch

Species Code: ASAR7

Origin: endemic to the Palouse region in eastern Whitman County and adjacent parts of Idaho, although disjunct populations occur in central Washington.

Rare: A. arrectus is ranked S2 by both the Natural Heritage Program in Washington and the Conservation Data Center in Idaho.

Form: forb, perennial, erect, 30-50 cm tall, sparsely appressed pubescent overall, with a woody taproot and caudex.

Duration: perennial

Habitat Type: prairie, shrub thickets

Wetland Indicator Status: not listed

Leaves: pinnate compound, 9-22 cm long; leaflets 17-32, but usually 21-31, oblong to elliptical, glabrous above, peduncles longer than the leaves.

Mature height: 12-20 inches

Flowers: borne in dense, erect raceme of 15-35 flowers; corolla whitish, 12-13 mm long.

Flower color: white to pale yellow

Bloom: late May to early June

Bloom starts on: late May

Bloom ends on: early June

Fruit: linear, 12-20 mm long, stipate, the suture nearly dividing the pod; seeds 2 mm, olive-brown, reniform.

Characteristics:
Astragalus palousensis Piper is synonymous.
A. palousensis in Piper & Beattie 1914, Hitchcock et al 1969.
Reproduces sexually by seed.
n=24 (Hu et al 1999).
Pollinated by insects.
Flowers are perfect.
Fruit is a legume.
Some Astragalus species are toxic to livestock.
Larva of the clouded sulfur (Colias philodice), the silvery blue (Glaucopsyche lygdamus), the western tailed blue (Everes amyntula), and the arrowhead blue (Glaucopsyche piasis) butterflies feed on Astragalus species. While they prefer alfalfa, larva of the orange sulfur butterfly (Colias eurytheme) may also feed on Astragalus species (Pocewicz 2005).

Comments:
Worldwide, Astragalus is the largest genus of vascular plants, numbering around 2500 species. Around 400 of these occur in North America. Most are narrow endemic species specifically adapted to a particular set of habitat conditions (Hu et al 1999).

Sun requirement: full

Soil moisture: xeric to mesic

Fire: Some Astragalus spp. resist fire by having deep taproots and the ability to form new shoots from the taproot. The new shoots will produce seed the year following a fire (McLean 1969).

Hazards: Some Astragalus species are toxic to livestock.

Sowing time: spring

Transplant time: spring

Stratification: seed should be scarified.

Seed yield: high

Seed harvest: moderate difficulty

Seed first harvest: third season

Seed cleaning: easy

Planting duration: medium

Seed shatter: medium

Seed size: medium

Seed harvest date: early July

Herbaria: Specimen data and digital resources from The Consortium of Pacific Northwest Herbaria

Propagation:
1 protocol in the Native Plant Network
Pullman, Washington Plant Materials Center
Reproduces sexually by seed.

Notes: Astragalus arrectus is a rare species endemic to the Palouse. It should not be collected. Other names include Palouse milkvetch, Astragalus palousensis (Skinner et al 2005).

References:
Hitchcock, C. Leo, Arthur Cronquist, Marion Ownbey, and J.W. Thompson. 1969. Vascular Plants of the Pacific Northwest. University of Washington Press. Seattle, WA. 5 vol.

Hu, Jer-Ming, Michael J. Sanderson, and Martin F. Wojciechowski. 1999. Website for the Largest Genus of Vascular Plants, Astragalus. University of California, Davis. Online at http://ginger.ucdavis.edu/astragalus/astragalus_home.htm Accessed 10/29/06.

McLean, Alastair. 1969. Fire Resistance of Forest Species as Influenced by Root Systems. Journal of Range Management 22:120-122.

Piper, C.V., and R.K. Beattie. 1914. The Flora of Southeastern Washington and Adjacent Idaho. Lancaster, PA: Press of the New Era Printing Company. 296 pp.

Pocewicz, Amy. 2005. Host Plants of Palouse Butterfly Species. 2 page handout to accompany the April 2005 presentation to the Palouse Prairie Foundation.

Skinner, David M., Paul Warnick, Bill French, and Mary Fauci. 2005. More Palouse Forbs for Landscaping. USDA NRCS Pullman Plant Materials Center and Palouse Prairie Foundation. Online at http://www.wsu.edu/pmc_nrcs/Docs/More_Forbs_for_Landscaping.pdf

Links:
Plant Profile from the USDA PLANTS Database
Washington Natural Heritage Program Field Guide to Selected Rare Plants Astragalus arrectus species information