Astragalus humillimus - Gray
Mancos Milkvetch
Taxonomic Status: Accepted
Related ITIS Name(s): Astragalus humillimus Gray (TSN 25539)
Unique Identifier: ELEMENT_GLOBAL.2.147602
Element Code: PDFAB0F440
Informal Taxonomy: Plants, Vascular - Flowering Plants - Pea Family
Image 12081

Public Domain

 
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 humillimus
Conservation Status
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NatureServe Status

Global Status: G1
Global Status Last Reviewed: 10Sep2011
Global Status Last Changed: 19Jan1984
Rounded Global Status: G1 - Critically Imperiled
Reasons: A narrow endemic of the Four Corners region. All the populations are in an area being intensively developed for energy resources. Declines from 1989 to 2008 have been observed. Threats have increased.
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), Navajo Nation (S1), New Mexico (S1)

Other Statuses

U.S. Endangered Species Act (USESA): LE: Listed endangered (27Jun1985)
U.S. Fish & Wildlife Service Lead Region: R2 - Southwest

NatureServe Global Conservation Status Factors

Range Extent Comments: Known from San Juan County, New Mexico and Montezuma County, Colorado. Occurrences in New Mexico are in a 20 square mile area. In Colorado occurrences are within a 13 square mile area.

Area of Occupancy: 6-125 4-km2 grid cells
Area of Occupancy Comments: Approximately 12 4-sq km grid cells (EO data in the NatureServe central database as of July 2011).

Number of Occurrences: 6 - 20
Number of Occurrences Comments: In New Mexico, there are approximately 13 occurrences on the Navajo Nation (EO data in the NatureServe central database as of July 2011; USFWS 2011). Colorado has four historical occurrences on Ute Mountain Ute tribal lands; access to these has been restricted since 1987 (EO data in the NatureServe central database as of July 2011; USFWS 2011).

Population Size Comments: In 2007/2008, less than 400 plants total were found in 12 populations on the Navajo Nation and only 2 of the 12 populations had more than 50 live plants (Navajo Natural Heritage Program 2008, Navajo Nation Department of Fish and Wildlife 2009 cited by USFWS 2011).

Number of Occurrences with Good Viability/Integrity: Unknown

Overall Threat Impact: Very high - high
Overall Threat Impact Comments: Major threats include energy exploration, development, and maintenance activities, transmission line installation and maintenance, and off-road vehicle use (Knight and House 1989; USFWS 2011). As of 2011, threats such as energy development, transmission lines, and off-road vehicle use are more numerous and immediate than they were in 1985 (USFWS 2011). Nearly all known and potential habitat may be affected by natural gas or oil exploration and development (USFWS 2011). Vehicles drive over and crush individual plants and break apart sandstone areas that contain tinajas, which are required for seedling establishment (Navajo Nation Department of Fish and Wildlife 2009 cited by USFWS 2011).

Short-term Trend: Decline of >10%
Short-term Trend Comments: The overall population trend appears to be declining in New Mexico (USFWS 2011). "Population numbers have not returned to the earliest field estimations (approximately10,000 on Navajo Nation lands as of 1989), and decreased dramatically after the 2002-2003 drought (less than 400 on Navajo Nation lands as of 2008)" (USFWS 2011). Elliot 2013 reported significant mortality at known sites (up to 66% mortality), with no evidence of ground disturbance, disease or herbivory; he attributes decline to either drought or low temerpatures. 

Long-term Trend: Unknown

Intrinsic Vulnerability Comments: Research has shown that this species has low fecundity (USFWS 2011). In addition, there has been no long-term propagation success despite numerous attempts (USFWS 2011).

Environmental Specificity: Very narrow. Specialist or community with key requirements scarce.
Environmental Specificity Comments: Highly restricted habitat; doesn't tolerate disturbance.

Other NatureServe Conservation Status Information

Distribution
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Global Range: Known from San Juan County, New Mexico and Montezuma County, Colorado. Occurrences in New Mexico are in a 20 square mile area. In Colorado occurrences are within a 13 square mile area.

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, NM, NN

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
CO Montezuma (08083)
NM San Juan (35045)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
14 Middle San Juan (14080105)+, Chaco (14080106)+, Mancos (14080107)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A perennial herb that grows in low, tufted mats, 3-4.5 dm in diameter. Flowering occurs only for a brief time in late April or early May. Flowers are lavender with white veins and have a sweet-pungent smell. This species is apparently very attractive to butterflies, which have been seen to blanket the plants when they are in bloom.
General Description: Diminutive, tufted perennial forming clumps up to 30 cm across; crown with persistent, spiny leaf stalks; stems up to 1 cm long, leaves crowded, up to 4 cm long, with 7-11 oval leaflets, these 0.7-2.0 mm long; flower branches short, 1-3 flowers; calyx about 3 mm long, withered leaves persistent as spiny projections from the stem base, petals lavender to purplish, with a conspicuous lighter-colored spot in the throat of the corolla tube; pod spreading, egg shaped, about 4.5 mm long, 2 mm wide (Spackman et al. 1997). The species is reported to have a sweet-pungent smell.
Technical Description: Diminutive, tufted perennial forming clumps up to 30 cm across; crown with persistent, spiny leaf stalks; stems up to 1 cm long, leaves crowded, up to 4 cm long, with 7-11 oval leaflets, these 0.7-2.0 mm long; flower branches short, 1-3 flowers; calyx about 3 mm long, withered leaves persistent as spiny projections from the stem base, petals lavender to purplish, with a conspicuous lighter-colored spot in the throat of the corolla tube; pod spreading, egg shaped, about 4.5 mm long, 2 mm wide.
Diagnostic Characteristics: No other mat-forming Astragalus has persistent spinescent leaf stalks.
Duration: PERENNIAL
Reproduction Comments: Breeding system: Fruit set 30% when caged, so capable of selfing but with reduced fruit set (60% when deliberately crossed geitenogamously or xenogamously). Pollinators: Vanessa cardui, the painted lady butterfly, visits frequently but does not appear to be a pollinator (S. Geer, pers. comm., 18 Dec. 1990); Hymenoptera is probably the most important group, especially Osmia and Tetralonia bees; Diptera sometimes seen but probably not significant.
Known Pests: BRUCHIDAE AND LEPIDOPTERA LARVAE SEEN ON SEED PODS AND SEEDS
Ecology Comments: Astragalus humillimus occurs on Point Lookout and Cliff House sandstones, and tan Cretaceous sandstones of the Mesa Verde series. Dominant associated species are Oryzopsis hymenoides, Gutierrezia sarothrae, Yucca angustissima, and Artemisia tridentata. This species is apparently very attractive to butterflies, which have been seen to blanket the plants when they are in bloom.
Terrestrial Habitat(s): Bare rock/talus/scree, Desert, Sand/dune
Habitat Comments: Sandstone ledges or mesa tops, often in cracks in the sandstone substrate or in shallow pockets of sandy soil. Typically on large, nearly flat sheets of exfoliating Point Lookout and Cliffhouse Sandstone (Roth 2008). Possibly also on limestone. Approximately 1695 m.
Economic Attributes
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Economically Important Genus: Y
Management Summary
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Stewardship Overview: Develop plans to avoid and minimize impacts from energy development and off-road vehicle activities (USFWS 2011). Enforce mitigation and conservation measures. Continue survey and monitoring efforts. Collect seed for seed banking (USFWS 2011).
Population/Occurrence Delineation
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Minimum Criteria for an Occurrence: A natural occurrence of one or more plants.
Separation Barriers: Unsuitable habitat or altered areas; or markedly distinct features on the landscape such as ridges, rivers, or roads.
Separation Distance for Unsuitable Habitat: 1 km
Separation Distance for Suitable Habitat: 2 km
Separation 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 occurrences will eventually be found to be more closely connected. No information on mobility of pollen and propagules is available on which to base the separation distance for this species.
Date: 08Sep2003
Author: Jill Handwerk
Population/Occurrence Viability
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Excellent Viability: Size: 5000 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. This includes the presence of the appropriate, very specific edaphic requirements of this species, i.e., depressed pockets of sandy soils derived from the Point Lookout and Cliff House sandstones of the Mesa Verde series.

Good Viability: Size: 1000 to 4999 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: 50 to 999 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 moderate human disturbance, but the ecological processes needed to sustain the species are still intact.

Poor Viability: Size: Less than 50 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.

Justification: Large populations in high quality sites ("A", "B" or "C" ranked EOs) 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. "D" ranked occurrences have a low probability of long-term persistence due to inbreeding depression, natural stochastic events, and their intrinsic vulnerability to human impacts.
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: 14Sep2011
NatureServe Conservation Status Factors Author: Jill Handwerk, rev. A. Tomaino (2011), rev. J. Handwerk (2015)
Management Information Edition Date: 09Sep2011
Management Information Edition Author: Tomaino, A.
Element Ecology & Life History Edition Date: 12May2010
Element Ecology & Life History Author(s): Parker, J. (2010), 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 Natural Heritage Program. 2003. Biological Conservation Datasystem. Colorado State University, Ft. Collins, CO.

  • Elliott, B. A., S. Spackman Panjabi, B. Kurzel, B. Neely, R. Rondeau, M. Ewing. 2009. Recommended Best Management Practices for Plants of Concern. Practices developed to reduce the impacts of oil and gas development activities to plants of concern. Unpublished report prepared by the Rare Plant Conservation Initiative for the National Fish and Wildlife Foundation.

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

  • 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.

  • Knight, P. J. 1989. Mancos milkvetch recovery plan. Unpublished report prepared for the US Fish and Wildlife Service, Alburquerque, NM.

  • Knight, P., and D. House. 1989. Mancos Milkvetch (Astragalus humillimus) Recovery Plan. Prepared for the U.S. Fish & Wildlife Service, Region 2, Albuquerque, NM.

  • Knight, P.J. 1981. Status report - Astragalus humillimus. New Mexico State Heritage Program.

  • Natural Heritage New Mexico. 2003. Biological Conservation Data. University of New Mexico, Albuquerque, NM.

  • 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.

  • Neely, E.E. 1987. Astragalus humillimus inventory. Unpublished report prepared for the Colorado Natural Areas Program, Denver, CO.

  • New Mexico Native Plant Protection Advisory Committee. 1984. A handbook of rare and endemic plants of New Mexico. Univ. New Mexico Press, Albuquerque. 291 pp.

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

  • Roth, D. 2008. May 15 last update. Species account for Astragalus humillimus. Navajo Natural Heritage Program, Window Rock, AZ. [http://nnhp.nndfw.org/Plants/ashu.pdf]

  • Roth, Daniela. October 17, 1998. Personal communication to Martha Martinez through electronic mail: plants endemic or mostly ocurring in Navajo Nation lands. Botanist for the Navajo Nation Heritage Program.

  • Schneider, A. 2013. Wildflowers, Ferns, and Trees of the Four Corners Regions of Colorado, New Mexico, Arizona, and Utah. Accessed on-line at http://www.swcoloradowildflowers.com.

  • Sivinski, R., and K. Lightfoot. 1995. Endangered plant study performance report E9. U.S. Fish and Wildlife Service, Albuquerque, New Mexico.

  • 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.

  • U.S. Fish and Wildlife Service. 1985. Final rule to determine Astragalus humillimus to be endangered. Federal Register 50(124): 26568-26572.

  • U.S. Fish and Wildlife Service. 2011. Mancos milkvetch (Astraglus humillimus) 5-year review summary and evaluation. July 2011. New Mexico Ecological Services Office, Alburquerque, New Mexico. [http://ecos.fws.gov/docs/five_year_review/doc3829.pdf]

  • 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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