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Astragalus micromerius
(Chaco milkvetch)

[taxon report][distribution map][all photos][line drawing]



Family: Fabaceae

Scientific Name: Astragalus micromerius Barneby

Synonyms: None

Vernacular Name: Chaco milkvetch

R-E-D Code: 1-1-3

Description: Perennial herb; stems 5-30 cm long, prostrate, silvery-hairy, bearing densely crowded small leaves; leaves 4-20 mm long, pinnately compound with 3-9 leaflets; flowers usually solitary or in pairs, pea-like, about 6 mm long, petals greenish-white with pale purple veins or tips; pods ovoid, 4-5 mm long, slightly longer than broad, unilocular, the tip forming a flattened beak. Flowers July and August.

Similar Species: Astragalus humistratus and A. chuskanus both have a similar prostrate (humistrate) growth form, but both have leaves and flowers at least twice the size of A. micromerius. Also, most of the hairs of A. humistratus are attached in the middle leaving both ends free (dolabriform), whereas A. micromerius and A. chuskanus have basally attached hairs.


Distribution: New Mexico, McKinley, Rio Arriba, and San Juan counties.

Habitat: Gypseous or limy sandstones in piņon-juniper woodland or Great Basin desert scrub; 2,000-2,250 m (6,600-7,300 ft).

Remarks: This diminutive endemic is usually associated with outcrops of sandstone that are blended with Todilto gypsum or limestone. It has a fairly wide range, but is sporadically distributed in isolated populations.

Conservation Considerations: Not significantly threatened by the prevailing land uses within its habitats.

Important Literature (*Illustration):

Barneby, R.C. 1964. Atlas of North American Astragalus. Memoirs of the New York Botanical Garden 13:1-1188.

Isely, D. 1998. Native and naturalized Leguminosae (Fabaceae) of the United States. Monte L. Beane Life Science Museum, Brigham Young University, Provo, Utah.

*New Mexico Native Plants Protection Advisory Committee. 1984. A handbook of rare and endemic plants of New Mexico. University of New Mexico Press, Albuquerque.

Information Compiled By: Robert Sivinski, 1999

Agency Status:
Taxon USFWS State of NM USFS BLM Navajo Nation Natural Heritage NM Global Rank
Astragalus micromeriusSoCSoCSen..S2G2


Photo credits in header Peniocereus greggii var. greggii © T. Todsen,
Lepidospartum burgessii © M. Howard, Argemone pleiacantha ssp. pinnatisecta © R. Sivinski
©2005 New Mexico Rare Plant Technical Council