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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 calycosus

Astragalus calycosus

Astragalus calycosus
Fabaceae (Pea Family)

Semi-desert-montane.  Openings.  Spring.
Canyons of the Ancients National Monument, April 19, 2007 and April 6, 2012.

Astragalus calycosus
Astragalus calycosus
Fabaceae (Pea Family)

Semi-desert-montane.  Openings.  Spring.
Canyons of the Ancients National Monument, April 19, 2007.

Astragalus calycosus most often forms a symmetrically round mat of light green, oval, hairy leaves surmounted by numerous leafless flower stalks which lean outward encircling the mound of leaves.  The plant is at home in rocks and sand in the lower Pinyon/Juniper forests and in mountain soils.  It can put on a magnificent bloom, covering hundreds of square feet with many dozens of plants.

John Torrey named this plant in 1871 from a specimen Sereno Watson collected in 1868.  "Calycosus" probably refers to some aspect of the calyx.

Astragalus calycosus
Astragalus calycosus
Fabaceae (Pea Family)

Semi-desert-montane.  Openings.  Spring.
Canyons of the Ancients National Monument, April 19, 2007.

Two further characteristic that help identify A. calycosus are the lobed white wing petals and the usually straight, rounded at the bottom, 1-2.5 cm long, hairy seed pods.

 

Astragalus calycosus
Astragalus calycosus
Fabaceae (Pea Family)

Semi-desert-montane.  Openings.  Spring.
Canyons of the Ancients National Monument, May 12, 2011.

A magnificent year for Astragalus calycosus flowers is followed by a magnificent year for seed production.

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
Eradicated

Questionable presence

Range map for Astragalus calycosus

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