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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, causing 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 bisulcatus variety major
Astragalus bisulcatus variety major  
Fabaceae (Pea Family)

Foothills, montane. Meadows. Spring, summer.
Roaring Fork Road, August 10, 2011.

In the Four Corners states, especially in southwest Colorado, this Astragalus is much less common than its very close cousin shown below.  Astragalus bisulcatus variety major is often found on drier sites, in smaller numbers, with slightly larger flowers, and larger leaves and leaflets.  When growing conditions are optimum, as shown in the photograph at left, this species can spread over dozens of square feet, growing to nearly three feet tall.

William Jackson Hooker named this plant Phaca bisulcatus in 1831 from a specimen collected by Thomas Drummond on the "Plains of the Saskatchewan"  around 1826.  (Quotation from Intermountain Flora).  Asa Gray renamed the plant Astragalus bisulcatus in 1861.  "Bisulcatus" is Latin for "two-grooved" and refers to the deep groove on both sides of the seed pod.

Astragalus bisulcatus variety major
Astragalus bisulcatus variety major  
Fabaceae (Pea Family)

Foothills, montane. Meadows. Spring, summer.
Roaring Fork Road, August 10, 2011.

Astragalus bisulcatus variety major

Astragalus bisulcatus variety major

Astragalus bisulcatus variety major

Astragalus bisulcatus variety major  
Fabaceae (Pea Family)

Foothills, montane. Meadows. Spring, summer.
Top and bottom left: Roaring Fork Road, September 27, 2014.
Middle: Roaring Fork Road, August 10, 2011.

Pod hairs are short, white, and upright. Grooves in the pods are quite visible.

Astragalus bisulcatus variety haydenianus

Astragalus bisulcatus variety haydenianus

Astragalus bisulcatus variety haydenianus.  Synonym: Astragalus haydenianus.
Fabaceae (Pea Family)

Foothills, montane. Meadows, roadsides. Spring, summer.
Near Lone Mesa State Park, June 11, 2008.

This species can be abundant in masses, especially along roadsides in the lower montane region.  It has far more but smaller flowers than A. bisulcatus variety major shown above, and it has a distinctive vertical growth pattern to its flower stems but an arching growth pattern to its leaves. Lower stems are often tinged red. 

Both varieties shown on this page prefer selenium rich soils and have the characteristic selenium odor.

Asa Gray named this species in 1876 from a specimen collected by Townshend Brandegee on the 1874 Hayden Survey in the La Plata Mountains (between present day Durango and Mancos, Colorado).  William Weber calls this plant "Astragalus haydenianus".  Kartesz, Welsh, and the authors of Intermountain Flora call it "Astragalus bisulcatus variety haydenianus".

Astragalus bisulcatus variety haydenianus
Astragalus bisulcatus variety haydenianus.  Synonym: Astragalus haydenianus.
Fabaceae (Pea Family)

Foothills, montane. Meadows, roadsides. Spring, summer.
Near Lone Mesa State Park, June 11, 2008.

Astragalus bisulcatus variety haydenianus
Astragalus bisulcatus variety haydenianus.  Synonym: Astragalus haydenianus.
Fabaceae (Pea Family)

Foothills, montane. Meadows, roadsides. Spring, summer.
Near Lone Mesa State Park, June 11, 2008.

Flower keel tips are purple spotted; the calyx tube surrounding the base of each flower has black, appressed hairs; and flower stems are packed with numerous tiny flowers about 8 millimeters in total length.

Astragalus bisulcatus variety haydenianus

Astragalus bisulcatus variety haydenianus.  Synonym: Astragalus haydenianus.
Fabaceae (Pea Family)

Foothills, montane. Meadows, roadsides. Spring, summer.
Along Highway 184, June 17, 2010 and Lone Mesa State Park, August 4, 2008.

Pods are hairy, flattened, 6-9 millimeters long, and pendulous.  One side of the pod has a slightly raised keel along the suture line and the other side has a very prominent keel.  The keel is evident even in young green pods.  (Instead of indicating that the pod has a keel, we could say that the pod has two indentations (bi-sulcate) on either side of the suture).

Astragalus bisulcatus variety haydneianus

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 bisulcatus

Astragalus bisulcatus variety haydenianus

Range map for Astragalus bisulcatus variety haydenianus

Astragalus bisulcatus variety major

Range map for Astragalus bisulcatus variety major