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Plant Profile

Cotton's Milkvetch (Astragalus cottonii)

Astragalus australis var. olympicus with developing pods. Photo Credit: Mark Sheehan
  • Global Rank: G2 - Imperiled
  • Legal Status: N/A
  • Family: Fabaceae
  • State: WA
  • Nature Serve ID: 147601
  • Lifeform: Forb/herb
  • Date Inducted in National Collection: 03/08/1989
Description:

Even though Astragalus australis var. olympicus is native only to high reaches in the Olympic Mountains of Washington, it is not immune to the impact that modern humans have had on the ecosystem. With an unfortunate lack of foresight, 12 mountain goats were introduced to the Olympic Mountains in the 1920s to provide animals for sport hunting. The original population of 12 has now grown to over 1,000 individuals. Mountain goats are not part of the native ecosystem in the Olympic Mountains, and consequently, the flora of the region is not adapted to the stresses that goats put on the plants. Astragalus australis var. olympicus is no exception. While the Olympic Peninsula encompasses only 8% of Washingtons land, it contains 27% of the states rare flora. Olympic National Park has an even higher concentration of rare plants: 19% of the rare plants here are found in just over 2% of the state (Schreiner et al. 1994). This concentration of rare flora exists because small islands of habitat were not covered by ice or water during the last ice age. Mountain flora isolated in this habitat could not interbreed with other populations, and eventually evolved into its own distinct taxa. Isolated high in the Olympic Mountains during the last ice age, this particular variety of A. australis evolved a unique trait: highly inflated seedpods. These seed pods have been likened to "mini greenhouses," increasing the temperature surrounding the developing seeds. This variety has not been isolated long enough to evolve into a separate species, but it is possible that this species will become distinct enough to become its own species if it continues to be isolated and cannot interbreed with other populations of A. australis (Schreiner et al. 1994).

Where is Cotton's Milkvetch (Astragalus cottonii) located in the wild?

Habitat:

South-facing talus slopes, ridges, and knolls comprised of calcareous substrates derived from sea-floor sediments (limestone) with a pH nearly always higher than 6. The region is characterized as sub-alpine, with an elevation of 4800 to 6000 ft (1460-1830m). The sub-alpine prairie association includes species such as Phlox diffusa, Festuca idahoensis, Allium crenulatum, and Lomatium martindalei.

Distribution:

Olympic Peninsula of Washington

States & Provinces:

Cotton's Milkvetch can be found in Washington

Which CPC Partners conserve Cotton's Milkvetch (Astragalus cottonii)?

  • University Of Washington Botanic Gardens

    Not Sponsored
    Assigned 06/09/17
    • CPC's Plant Sponsorship Program provides long term stewardship of rare plants in our National Collection. We are so grateful for all our donors who have made the Plant Sponsorship Program so successful. We are in the process of acknowledging all our wonderful plant sponsorship donors on our website. This is a work in progress and will be updated regularly.

    Conservation Actions

    • 08/21/2020
      • Propagation Research

    Seed germination studies at The Berry Botanic Garden. Seeds were scarified and then subjected either to no cold stratification or 8 weeks of cold stratification followed by either constant 68F (20C) or alternating 50F/68F (10C/20C) temperatures. 100% of the seeds without cold stratification germinated regardless of temperature regime. 80% of seeds subjected to cold stratification germinated regardless of subsequent temperature regime (BBG File).

    • 08/21/2020
      • Reproductive Research

    Pollinator exclusion in the field significantly reduced fruit set but seed set per fruit was not significantly affected (Kaye 1989).

    • 08/21/2020
      • Demographic Research

    Extensive research on the ecology, reproduction and demography of Cottons milkvetch (Kaye 1989). Pollinator exclusion in the field significantly reduced fruit set but seed set per fruit was not significantly affected (Kaye 1989). Demographic monitoring from 1985 to 1988 within permanent plots revealed a significant decrease in population numbers. The cause of the decline is not known. Mountain goat grazing and wallowing was one speculative explanation. Low snowpack and summer drought was favored by the researcher as the most likely cause (Kaye 1989). Transition matrix modeling projected that populations would continue to decline (Kaye 1989). In order to evaluate the effects of mountain goats, ten permanent plots were established. All Astragalus australis var. olympicus plants were mapped and counted in these plots, and grazing or physical injuries were recorded from 1985 to 1991. Monitoring results revealed that A. australis var. olympicus was grazed in more than half of the sub-populations, and that injuring was sporadic but sometimes intense. Sub-populations were more or less stable during the six-year period, but the study was not long enough to determine long term trends (Schreiner et al. 1994).

    • 08/21/2020
      • Orthodox Seed Banking

    Seeds from three locations stored at The Berry Botanic Garden.

    Nature Serve Biotics
    • 05/02/2017

    Endemic to higher elevations in the northern Olympic Mountains of Washington State. Threatened by non-native mountain goats, which trample the native vegetation. Potentially threatened by over-use of the area by hikers.

    Edward Guerrant, Ph.D.
    • 01/01/2010

    Disturbance (herbivory and trampling) from non-native mountain goats (WNHP 1999) Trampling by hikers (WNHP 1999)

    Edward Guerrant, Ph.D.
    • 01/01/2010

    As of 1996: 10 populations on the Olympic Peninsula. Surveys were conducted between 1981 and 1996. Numbers ranged from as low as 9 to as high as 2000, with a total of approximately 5,300 individuals (WNHP 2000).

    Edward Guerrant, Ph.D.
    • 01/01/2010

    Extensive research on the ecology, reproduction and demography of Cottons milkvetch (Kaye 1989). Pollinator exclusion in the field significantly reduced fruit set but seed set per fruit was not significantly affected (Kaye 1989). Demographic monitoring from 1985 to 1988 within permanent plots revealed a significant decrease in population numbers. The cause of the decline is not known. Mountain goat grazing and wallowing was one speculative explanation. Low snowpack and summer drought was favored by the researcher as the most likely cause (Kaye 1989). Transition matrix modeling projected that populations would continue to decline (Kaye 1989). In order to evaluate the effects of mountain goats, ten permanent plots were established. All Astragalus australis var. olympicus plants were mapped and counted in these plots, and grazing or physical injuries were recorded from 1985 to 1991. Monitoring results revealed that A. australis var. olympicus was grazed in more than half of the sub-populations, and that injuring was sporadic but sometimes intense. Sub-populations were more or less stable during the six-year period, but the study was not long enough to determine long term trends (Schreiner et al. 1994). Seed germination studies at The Berry Botanic Garden. Seeds were scarified and then subjected either to no cold stratification or 8 weeks of cold stratification followed by either constant 68F (20C) or alternating 50F/68F (10C/20C) temperatures. 100% of the seeds without cold stratification germinated regardless of temperature regime. 80% of seeds subjected to cold stratification germinated regardless of subsequent temperature regime (BBG File).

    Edward Guerrant, Ph.D.
    • 01/01/2010

    No active management. Seeds from three locations stored at The Berry Botanic Garden.

    Edward Guerrant, Ph.D.
    • 01/01/2010

    Monitor known occurrences for population trends (WNHP 1999). Conduct field searches to locate new populations (WNHP 1999). If population sizes continue to decline, seedling recruitment may be increased by removing mountain goats from the area, controlling pre-dispersal predators, sowing extra seeds, and tending established plants (Kaye 1989).

    Edward Guerrant, Ph.D.
    • 01/01/2010

    Collect and store seeds from across range. Determine propagation and reintroduction protocols.

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    Nomenclature
    Taxon Astragalus cottonii
    Authority M.E. Jones
    Family Fabaceae
    CPC Number 390
    ITIS 25479
    USDA ASCO13
    Duration Perennial
    Common Names Cotton's milkvetch
    Associated Scientific Names Astragalus australis var. olympicus | Astragalus australis var. cottonii | Astragalus cottonii | Astragalus cottoni | Astragalus olympicus | Atelophragma cottonii
    Distribution Olympic Peninsula of Washington
    State Rank
    State State Rank
    Washington S2
    Ecological Relationships

    Photos

    Astragalus australis var. olympicus with developing pods. Photo Credit: Mark Sheehan

    Up-close view of Astragalus australis var. olympicus flowers. Photo Credit: Nelsa Buckingham

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