Astragalus species are difficult to identify and it is the seed pod, not the flower, that is often crucial in the identification process.

     The common name, "Locoweed", is applied not to one plant but to many members of the Astragalus genus, for many of these plants absorb toxic soil substances, especially selenium, which cause grazing animals a variety of serious ailments.  Further complicating the common name: some people use the name "Locoweed" not only for Astragalus but also for another Pea genus, Oxytropis.  And, making common names even more confusing, many Astragalus also carry the common name of "Milk Vetch" (easily confused with other Peas known as "Vetch").  These common names are so confusing that they really should not be used (except in whispers to close friends). 

    The genus was named by Linnaeus in 1753 and the word "Astragalus" means "ankle bone" in Greek.  It is an ancient Greek plant name perhaps given because of  the seed shape in some members of the Astragalus genus or, the authors of Intermountain Flora conjecture, because the Greeks used rattling bones for dice and the sound made is similar to the rattling of dry Astragalus seeds in the pod.

Astragalus missouriensis variety amphibolus
Fabaceae (Pea Family)

Semi-desert. Woodlands, shrublands, openings. Spring.
Near Narraguinnep Canyon, May 8, 2009.

Astragalus missouriensis inhabits dry hillsides and meadows from about 5,100 to 8,000 feet elevation in Pinyon/Juniper woods and Sagebrush meadows. 

Astragalus missouriensis is found from Alberta, Saskatchewan, and Manitoba southward to Texas.  Welsh points out that it is "remarkably uniform" in its characteristics throughout this entire area  --  except in the Four Corners region where it has "undergone taxonomically significant... morphological differentiation".  This differentiation may separate the various varieties of Astragalus missouriensis, but it is still quite difficult to distinguish Astragalus missouriensis variety amphibolus from Astragalus chamaeleuce and Astragalus amphioxys.  All three are found in the Four Corners region.

In 1818 Thomas Nuttall named and described Astragalus missouriensis from a specimen collected by Bradbury.  Twentieth century Astragalus expert Rupert Barneby, named and described variety amphibolus in 1947 from specimens collected near Mancos, Colorado by Baker, Earle, and Tracy.

Astragalus missouriensis often occurs in masses as shown on the next page of photographs. Click to see.

Astragalus missouriensis variety amphibolus
Fabaceae (Pea Family)

Semi-desert. Woodlands, shrublands, openings. Spring.
Blackrock Canyon, Navajo Reservation, Arizona, May 12, 2007.

Seed pods are sessile and are usually ascending (as pictured).  They are ellipsoid, 15-30 millimeters long, 5-9 mm thick, somewhat curved, hairy, pointed on one end, and moderately compressed.  Compare these seed pods, which are persistent, with Astragalus amphioxys seed pods which quickly fall of the plant.

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Questionable presence

Range map for Astragalus missouriensis