Astragalus microcymbus - Barneby
Skiff Milkvetch
Taxonomic Status: Accepted
Related ITIS Name(s): Astragalus microcymbus Barneby (TSN 25578)
Unique Identifier: ELEMENT_GLOBAL.2.155930
Element Code: PDFAB0F590
Informal Taxonomy: Plants, Vascular - Flowering Plants - Pea Family
 
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Dicotyledoneae Fabales Fabaceae Astragalus
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Concept Reference
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Concept Reference: Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Concept Reference Code: B94KAR01HQUS
Name Used in Concept Reference: Astragalus microcymbus
Conservation Status
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NatureServe Status

Global Status: G1
Global Status Last Reviewed: 05Sep2012
Global Status Last Changed: 19Oct1984
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G1 - Critically Imperiled
Reasons: Astragalus microcymbus is a narrowly restricted endemic from the Gunnison Basin, in south central Colorado. There are a total of about 10,000 individuals. Rabbit herbivory is heavy.
Nation: United States
National Status: N1

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Colorado (S1)

Other Statuses

U.S. Endangered Species Act (USESA): C: Candidate (05Dec2014)
U.S. Fish & Wildlife Service Lead Region: R6 - Rocky Mountain

NatureServe Global Conservation Status Factors

Range Extent Comments: Colorado endemic known from Gunnison County, and extending into the edge of Saguache County. Estimated range is 168 square kilometers, calculated in GIS in 2008 by the Colorado Natural Heritage Program by drawing a minimum convex polygon around the known occurrences.

Area of Occupancy: 2-25 4-km2 grid cells
Area of Occupancy Comments: The total area occupied by the mapped occurrences is 384 acres (calculated by the Colorado Natural Heritage Program in 2012).

Number of Occurrences: 1 - 5
Number of Occurrences Comments: There are 6 principal occurrences documented in the Colorado Natural Heritage Program database. One of the occurrences has not been observed in over 20 years, and is considered historical.

Population Size Comments: Approximately 17,800 individuals have been documented within the element occurrences.

Number of Occurrences with Good Viability/Integrity: Few (4-12)
Viability/Integrity Comments: There are 5 occurrences with an A or B rank.

Overall Threat Impact: Very high - high
Overall Threat Impact Comments: Rabbit herbivory and recreational use by ORVs are considered to be the primary threats to the species (Rondeau et al. 2011). Denver Botanic Gardens monitoring data, along with Lyon (1990) indicate that rabbit herbivory is heavy and that rabbits may be selecting Astragalus microcymbus over other local plant species. About 20 miles of single track trails have been constructed within A. microcymbus habitat (pers. comm. Tom Grant 2006), with the potential to become popular with motorcyclists. Other recreational activities and grazing also pose possible threats. Astragalus microcymbus habitat is further fragmented by utility corridors, trails, roads, development, and cheat grass invasion.

Short-term Trend: Decline of 10-50%
Short-term Trend Comments: The Denver Botanic Gardens (DBG) has been monitoring 4 subpopulations of the species since 1995. Declines in population size have been documented (from 3000 to 50 in one plot), and are believed to be caused by drought and rabbit herbivory (CNHP 2005). Declines in population size have also been documented by other individuals since the early 1990's (CNHP 2006). In 2007 DBG conducted count-based and stage-based population viability analyses (PVA) with existing demographic data. The count-based PVA indicated that that the populations are declining at an average rate of 10% per year. A quasi-extinction threshold of 20 individuals was set for each population, and the time to extinction for the populations ranged from 12-35 years with all populations extirpated within 35 years after study initiation. 2008 was the 14th year in the study and immediate action is needed to prevent extirpation of these populations (DBG 2008).

Long-term Trend: Unknown
Long-term Trend Comments: Unknown

Intrinsic Vulnerability Comments: Astragalus microcymbus appears to be susceptible to herbivory or other unknown factors causing death of several hundred plants at a time. Since pollinator is unknown, other factors may be pertinent.

Other NatureServe Conservation Status Information

Distribution
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Global Range: Colorado endemic known from Gunnison County, and extending into the edge of Saguache County. Estimated range is 168 square kilometers, calculated in GIS in 2008 by the Colorado Natural Heritage Program by drawing a minimum convex polygon around the known occurrences.

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map

U.S. & Canada State/Province Distribution
United States CO

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
CO Gunnison (08051), Saguache (08109)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
14 Upper Gunnison (14020002)+, Tomichi (14020003)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A highly branched perennial herb, up to 3 dm tall. Flowers are white, tinged with purple; in bloom in May and June.
General Description: Herbaceous, perennial plants with purplish stems 2.5-6 dm long. Leaves are 2-4 cm long, leaflets are 3-9 mm long. Flowers are white, tinged with purple, and arranged in loose racemes of 7-14 flowers. Pods are terete and up to 8 mm long (Spackman et al. 1997).
Terrestrial Habitat(s): Shrubland/chaparral
Habitat Comments: Open sagebrush or juniper-sagebrush communities on moderately steep to steep slopes. Often found in rocky areas with a variety of soil conditions from clay to cobbles, gray to reddish in color (Spackman et al. 1997).  Associated plant taxa include Purshia tridentata,Yucca harrimaniae, Artemisia frigida, Chaenactis, Penstemon caespitosa, Symphoricarpos, Sedum lanceolatum, Phlox, Hesperia comata, Castilleja, and Poa.
Economic Attributes
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Economically Important Genus: Y
Management Summary Not yet assessed
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Population/Occurrence Delineation
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Minimum Criteria for an Occurrence: Any naturally occurring population that is separated by a sufficient distance or barrier from a neighboring population. As a guideline, EOs are separated by either: 1 mile or more across unsuitable habitat or altered and unsuitable areas; or 2 miles or more across apparently suitable habitat not known to be occupied. Justification: The rationale for this large a separation distance across suitable but apparently unoccupied habitat is that it is likely additional research will find this habitat to be occupied. It can often be assumed that apparently unconnected populations will eventually be found to be more closely connected; these are best regarded as suboccurrences. No information on mobility of pollen and propagules is available on which to base the separation distance for this species.
Date: 27Sep2000
Author: Spackman, S., and D. Anderson.
Population/Occurrence Viability
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Excellent Viability: Size: 1000 or more individuals (based on available EOR data). Condition: the occurrence has an excellent likelihood of long-term viability as evidenced by the presence of multiple age classes and evidence of flowering and fruiting, indicating that the reproductive mechanisms are intact. This occurrence should be in a high-quality site with less than 1% cover of exotic plant species and/or no significant anthropogenic disturbance. Landscape Context: the occurrence is surrounded by an area that is unfragmented and includes the ecological processes needed to sustain this species. A suitable natural disturbance regime (which may include fire), suitable soil chemistry and nutrient levels, and a lack of unnatural flooding is required by this species to persist. Justification: Large populations in high quality sites are presumed to contain a high degree of genetic variability, to have a low susceptibility to the effects of inbreeding depression, and to be relatively resilient.
Good Viability: Size: 100 to 1000 individuals (based on available EOR data). Condition: the occurrence should have a good likelihood of long-term viability as evidenced by the presence of multiple age classes and evidence of flowering and fruiting, indicating that the reproductive mechanisms are intact. Anthropogenic disturbance within the occurrence is minimal. If exotic species are present, they comprise less than 10% of the total ground cover. Landscape Context: the surrounding landscape should contain the ecological processes needed to sustain the occurrence but may be fragmented and/or impacted by humans.
Fair Viability: Size: 20 to 100 individuals (based on available EOR data). Condition: The occurrence may be less productive than the above situations, but is still viable, with multiple age classes and evidence of flowering and fruiting, indicating that the reproductive mechanisms are intact. The occupied habitat is somewhat degraded (exotic plant species make up between 10-50% of the total ground cover and/or there is a moderate level of anthropogenic disturbance). Landscape Context: there may be significant human disturbance, but the ecological processes needed to sustain the species are still intact.
Poor Viability: Size: Less than 20 individuals (based on available EOR data). Condition: little or no evidence of successful reproduction is observed (poor seedling recruitment, no flowering or fruiting observed, or poor age class distribution). Exotic plant species make up greater than 50% of the total ground cover, and/or there is a significant level of human disturbance. Landscape context: the surrounding area is fragmented with many ecological processes no longer intact. The occurrence has a low probability of long-term persistence due to inbreeding depression, natural stochastic events, and its intrinsic vulnerability to human impacts.
Justification: Justification: EOs not meeting "C"-rank criteria are likely to have a very high probability of inbreeding depression and extirpation due to natural stochastic processes and/or occur in degraded habitat with low long-term potential for survival.
Key for Ranking Species Element Occurrences Using the Generic Approach (2008).
U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 05Sep2012
NatureServe Conservation Status Factors Author: Spackman, Susan & KEP, rev. Maybury/Spackman (1996), rev. Handwerk, J. (2006), rev. Neuhaus, K., J. Handwerk, and S. Panjabi (2006), rev. Handwerk, J. (2009); rev. Handwerk, J. (2012)

Element Ecology & Life History Author(s): rev. SSP (2015)

Botanical data developed by NatureServe and its network of natural heritage programs (see Local Programs), The North Carolina Botanical Garden, and other contributors and cooperators (see Sources).

References
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  • Ackerfield, J. 2012. The Flora of Colorado. Colorado State University Herbarium. 433 pp.


  • Barneby, R.C. 1964. Atlas of North American Astragalus. 2 Vols. New York Botanical Garden, Bronx, New York. 1188 pp.

  • Colorado Native Plant Society. 1989. Rare plants of Colorado. Rocky Mountain Nature Association, Colorado Native Plant Society, Estes Park, Colorado. 73 pp.

  • Colorado Natural Heritage Program. 2005. The Second Annual Colorado Rare Plant Symposium: G1 Plants of Colorado. Symposium Minutes. Available on-line http://www.cnhp.colostate.edu/teams/botany.asp#symposia.

  • Colorado Natural Heritage Program. 2006. Biological Conservation Datasystem. Colorado State University, Ft. Collins, CO.

  • Denver Botanic Gardens. 2008. Demographic Analysis of Astragalus microcymbus (Fabaceae), an Endemic Species of Gunnison County, Colorado, USA.

  • Heil, K.D. and J.M. Porter. 1990. Status report for Astragalus microcymbus Barneby. January 2, 1990.

  • Johnston, B.C. 1979. USFS Summary Sheet. Unpublished report.

  • Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.

  • Lawrence, S. 1993 Endangered species petition. Unpublished report prepared for the US Fish and Wildlife Service, Washington, D.C..

  • Lyon, P. 1990. Field survey for Astragalus microcymbus.

  • Lyon, P. 1990. Field survey for Astragalus microcymbus.

  • Neely, B., S. Panjabi, E. Lane, P. Lewis, C. Dawson, A. Kratz, B. Kurzel, T. Hogan, J. Handwerk, S. Krishnan, J. Neale, and N. Ripley. 2009. Colorado Rare Plant Conservation Strategy, Developed by the Colorado Rare Plant conservation Initiative. The Nature Conservancy, Boulder, Colorado, 117 pp.

  • O'Kane, S. L. 1988. Colorado's Rare Flora. Great Basin Naturalist. 48(4):434-484.

  • Peterson, J. S., B.C. Johnston, and W. Harmon. 1981. Astragalus microcymbus status report of 3 March 1981.

  • Peterson, J.S. 1982 Plant Species of Special Concern, Astragalus microcymbus. Unpublished manuscript.

  • Rondeau, R., K. Decker, J. Handwerk, J. Siemers, L. Grunau, and C. Pague. 2011. The state of Colorado's biodiversity 2011. Prepared for The Nature Conservancy. Colorado Natural Heritage Program, Colorado State University, Fort Collins, Colorado. 

  • Spackman, S., B. Jennings, J. Coles, C. Dawson, M. Minton, A. Kratz, and C. Spurrier. 1997. Colorado rare plant field guide. Prepared for Bureau of Land Management, U.S. Forest Service and U.S. Fish and Wildlife Service by Colorado Natural Heritage Program.

  • US Fish and Wildlife Service. 1993 c. Memorandum to report on trip to Gunnison to visit Astragalus microcymbus and Astragalus anisus. USDOI, FWS, Ecological Services, Western Colorado Office, Grand Junction, CO. Unpublished report.

  • USDA, NRCS. 2013. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.

  • Weber, W. A. and R. C. Wittmann. 2012. Colorado Flora, Western Slope, A Field Guide to the Vascular Plants, Fourth Edition. Boulder, Colorado. 532 pp.

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