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    The Astragalus genus is large and complex.  In Colorado Flora, Western Slope William Weber lists over five dozen species with many sub-species.  The new Flora of the Four Corners lists fifty-eight species and several dozen varieties of Astragalus in the Four Corners drainage of the San Juan River.  In Intermountain Flora Arthur Cronquist lists 156 species and 122 varieties.  World-wide there are about 1600 species. 

    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 mollissimus

Astragalus mollissimus

Astragalus mollissimus

Astragalus mollissimus variety thompsoniae (Locoweed)
Fabaceae (Pea Family)

Semi-desert. Woodlands, shrublands, openings. Spring.
Above left: Canyons of the Ancients National Monument, April 1, 2005 and April 18, 2014.

Astragalus mollissimus is the most widespread and  common Astragalus in the Four Corners area.  It is characterized by hairy flower stems; numerous, hairy, small, light green leaflets, usually arching; numerous, long and narrow pink-purple flowers that have a pronounced backward flare at the upper tip of the rather small banner; and by short, plump, silver and pink very hairy seeds often curled into a ball. 

Astragalus mollissimus blooms early in the spring and by mid-summer the hairy seeds are prominent.  Where you find one plant you will usually find several, even many, as the second photograph above shows.  Note that all of the three dozen Astragalus mollissimus shown are first year plants from seeds that received abundant fall rains in 2013.  

"Mollissimus" is Latin for "very soft".  "Locoweed" refers to the plant’s effect on grazing animals, especially sheep.  Many species in the Astragalus genus are called "Locoweed". They are also called "Vetch" and "Milkvetch"  Since their are over 60 species of Astragalus in the Four Corners area, one can understand that such over-used common names are of no use if you wish to identify the actual species you are looking at.

Edwin James collected the first specimen of this plant along the Platte River in 1820 and John Torrey described and named it in 1827.

Astragalus mollissimus
Astragalus mollissimus variety thompsoniae (Locoweed)
Fabaceae (Pea Family)

Semi-desert. Woodlands, shrublands, openings. Spring.
Canyons of the Ancients National Monument, April 1, 2005.

Astragalus mollissimus
Astragalus mollissimus variety thompsoniae (Locoweed)
Fabaceae (Pea Family)

Semi-desert. Woodlands, shrublands, openings. Spring.
Canyons of the Ancients National Monument, May 13, 2004.

Astragalus mollissimus seed pods ripen slowly and are quite hairy.

 
Astragalus mollissimus
Astragalus mollissimus variety thompsoniae (Locoweed)
Fabaceae (Pea Family)

Semi-desert. Woodlands, shrublands, openings. Spring.
Canyons of the Ancients National Monument, September 19, 2005.

On sandy soils, brown, dried Astragalus mollissimus seed pods are scattered around dead stems flattened on the ground.

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 mollissimus