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  1. Family: Fabaceae Lindl.
    1. Genus: Astragalus L.
      1. Astragalus sinuatus Piper

        Whited's milkvetch is a white-flowered, perennial herb belonging to the pea and bean family (Leguminosae). The common name refers to Kirk Whited (born in 1852 in Michigan), who collected specimens of this species in Washington State and whose name is honoured in the specific epithet of the synonym, Astragalus whitedii. The specific epithet sinuatus refers to the sinuously wavy suture (seam along which the fruit opens) along the upper surface of the pod.

    [ILDIS]

    International Legume Database and Information Service

    Habit
    Perennial, Not climbing, Herb
    [KSP]

    Kew Species Profiles

    General Description
    Whited's milkvetch is a critically endangered legume, restricted to Washington State, USA.

    Whited's milkvetch is a white-flowered, perennial herb belonging to the pea and bean family (Leguminosae). The common name refers to Kirk Whited (born in 1852 in Michigan), who collected specimens of this species in Washington State and whose name is honoured in the specific epithet of the synonym, Astragalus whitedii. The specific epithet sinuatus refers to the sinuously wavy suture (seam along which the fruit opens) along the upper surface of the pod.

    Species Profile
    Geography and distribution

    Restricted to Washington State in the USA, Whited's milkvetch is found only along the western edge of the Columbia Basin in Chelan County. It occurs on rocky hillsides, growing in loess soils with small amounts of volcanic ash, at 250-610 metres above sea level.

    Description

    Overview:  Astragalus sinuatus is a robust, perennial herb with a woody taproot and knotty root-crown. The plant is covered with stiff hairs up to 0.6 mm long. Each plant has multiple stems that grow along the ground, but have the terminal branchlets bending upwards.

    Leaves:  The widely-spreading leaves are 2-7 cm long and are mostly sessile (borne directly on the stem and lacking a leaf stalk or petiole). Each leaf is composed of 11-17 flat or loosely folded leaflets each measuring 6-16 mm in length. 

    Flowers:  The inflorescence is a raceme of 8-16 flowers. The calyx (comprising a tube and five calyx teeth) is densely hairy, with black, or mixed black and white, hairs. The petals are whitish. The standard petal (banner) is 16.6-20 mm long and deeply notched at the apex; the two wing petals (each comprising a blade and basal claw) are 14.5-17.3 mm long; and the clawed keel petals are 12-13.4 mm long.

    Fruits: The mature fruit is a leathery to sub-woody pod, 2-3 cm long and 5-7 mm in diameter with a narrow, wavy suture along the upper surface and a cord-like suture along the lower surface (the upper and lower sutures together form the seam along which the fruit opens). There are 24-30 ovules (immature seeds) per pod.

    Seeds:  The seeds are smooth, dull brown and about 3.5 mm long.

    Threats and conservation

    This species is listed by the US Fish and Wildlife Service (USFWS) as a 'Species of Concern', and is Critically Endangered (CR) according to IUCN Red List criteria. An estimated 5,000 individuals of Astragalus sinuatus remained in the wild in 1994, although this number may have decreased since as a result of threats to its habitat. The invasion of non-native species (such as the grass Bromus tectorum ), grazing and agricultural development all threaten the dry hillside habitat in which it grows. Herbivorous insects are also a major threat, and although pods have the potential to produce up to 30 seeds, the presence of specialist and generalist seed predators means that in reality each pod often only contains one or two mature seeds.

    Periodic fires, on a 30-90 year cycle, probably played a role historically in maintaining the habitat of this species. The more frequent fires typical of recent years may promote weedy species at the expense of A. sinuatus . Suppression of fires and any increase in grazing could lead to invasion by sagebrush ( Artemisia tridentata ) and to a further decrease in A. sinuatus .

    Seeds from one population are held in the Berry Botanic Garden Seed Bank for Rare and Endangered Plants of the Pacific Northwest (Oregon, USA). Seeds are also held at the Miller Seed Vault at the University of Washington Botanic Gardens. The seed pods are so tough that it can take a pair of pliers to crack them open and extract the seed, and given that each pod normally contains only one or two seeds, seed-collecting can be quite a challenge!

    Conservation assessments carried out at Kew

    Astragalus sinuatus is being monitored as part of the 'IUCN Sampled Red List Index for Plants', which aims to produce conservation assessments for a representative sample of the world's plant species. This information will then be used to monitor trends in extinction risk and help focus conservation efforts where they are needed most.

    Distribution
    USA
    Ecology
    South-facing slopes of rocky hillsides; in loess soils with small amounts of volcanic ash.
    Conservation
    Critically Endangered (CR) according to IUCN Red List criteria.
    Hazards

    A small number of Astragalus species are toxic to livestock, but this is not likely to be the case for A. sinuatus, which is occasionally browsed by elk, deer and livestock.

    Images

    Distribution

    Native to:

    British Columbia, Washington

    Synonyms

    Common Names

    English
    Whited’s milkvetch

    Other Data

    Astragalus sinuatus Piper appears in other Kew resources:

    Bibliography

    First published in Bull. Torrey Bot. Club 28: 40 (1901)

    Accepted by

    • Govaerts, R. (1995). World Checklist of Seed Plants 1(1, 2): 1-483, 529. MIM, Deurne.

    Literature

    Kew Species Profiles

    • Combs, J. K., S. E. Reichard, M. J. Groom, D. L. Wilderman & Camp, P. A. (2011). Invasive competitor and native seed predators contribute to rarity of the narrow endemic Astragalus sinuatus. Ecological Applications 21: 2498–2509.
    • Contu, S. (2010). Astragalus sinuatus. Assessment using IUCN Categories and Criteria 3.1 (IUCN 2001). Royal Botanic Gardens, Kew.
    • Bjork, C.R. & Fishbein, M. (2006). Astragalus asotinensis (Fabaceae), a newly discovered species from Washington and Idaho, United States. Novon 16: 299-303.
    • Washington Natural Heritage Program (1997). Field Guide to Selected Rare Plants of Washington. Washington State Department of Natural Resources.
    • Barneby, R.C. (1964). Atlas of North American Astragalus. In: Mem. N. Y. Bot. Gard. 13: 315-316.

    Sources

    International Legume Database and Information Service
    International Legume Database and Information Service (ILDIS) V10.39 Nov 2011
    http://creativecommons.org/licenses/by/3.0

    Kew Backbone Distributions
    The International Plant Names Index and World Checklist of Selected Plant Families 2020. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
    © Copyright 2017 World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

    Kew Names and Taxonomic Backbone
    The International Plant Names Index and World Checklist of Selected Plant Families 2020. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
    © Copyright 2017 International Plant Names Index and World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

    Kew Species Profiles
    Kew Species Profiles
    http://creativecommons.org/licenses/by-nc-sa/3.0