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Click to read about the Astragalus genus.

Astragalus flavus

Astragalus flavus

Astragalus flavus

Astragalus flavus

Astragalus flavus

Astragalus flavus

Astragalus flavus (Yellow Milkvetch)
Astragalus Fabaceae (Pea Family)

Semi-desert, foothills. Shrublands, openings. Spring.
Above: Lower Cross Canyon, Utah, April 10 and May 2, 2016 and McElmo Canyon, Canyons of the Ancients National Monument, March 24, 2016.
Left: McElmo Canyon, Canyons of the Ancients National Monument, April 18, 2007 and April 16, 2012.

The light green, long leaves of Astragalus flavus grab your attention before the flowers emerge.  Individual small leaflets are narrow and widely spaced compared to those of most other Astragalus.  Flowers are numerous and on long, leafless, upright stems (although stems can be bent or arched, especially as they feel the weight of many flowers). 

"Flav" is Latin for "yellow". The type specimen flowers were yellow and in much of its territory Astragalus flavus flowers are yellow, but in the Four Corners area, flowers are white.   

A. flavus often grows in Selenium soils and dozens of plants with thousands of flowers can occur on these soils, as the photograph at the top of this page indicates.  

Thomas Nuttall (famed Harvard teacher, plant collector, and  taxonomist) collected the first specimen of this plant in the Rockies in the mid-1830s and published the description in 1838.

Astragalus flavus
Astragalus flavus (Yellow Milkvetch)
Fabaceae (Pea Family)

Semi-desert, foothills. Shrublands, openings. Spring.
McElmo Canyon, Canyons of the Ancients National Monument, March 27, 2005.

Astragalus flavus
Astragalus flavus (Yellow Milkvetch)
Fabaceae (Pea Family)

Semi-desert, foothills. Shrublands, openings. Spring.
McElmo Canyon, Canyons of the Ancients National Monument, April 27, 2005.

Astragalus flavus seed pods are compressed and have an obvious depression on one side.

 

Astragalus pattersonii

Astragalus pattersonii

Astragalus pattersonii  (Patterson's Milkvetch)
Fabaceae (Pea Family)

Foothills. Openings. Spring, summer.
Above: Near Lone Mesa State Park, May 13, 2017 and June 15. 2015.
Below: Mesa Verde National Park,
May 2, 2006.

It is common to have Astragalus pattersonii scattered across a broad area on gray Mancos Shale. Most of the plants growing in the barren-seeming gray Mancos Shale in the lower half of the photograph immediately above are Astragalus pattersonii. It is interesting to note that the white cast to the green area above the gray Mancos Shale is from Astragalus bisulcatus variety haydenii, another Astragalus that also favors the selenium soils of Mancos Shale. In the area of this photograph and other areas nearby, there were no Astragalus pattersonii growing on the deeper soils above the bare Mancos Shale and there were no Astragalus bisulcatus variety haydenii growing on the bare Mancos Shale.

Astragalus pattersonii thrives on the barren-seeming gray Mancos Shale at the base of a slight hill covered with a Gambel's Oak and Pinyon/Juniper forest near the entrance of Mesa Verde National Park.
Astragalus pattersonii
Astragalus pattersonii  (Patterson's Milkvetch)
Fabaceae (Pea Family)

Foothills. Openings. Spring, summer.
Left: Mesa Verde National Park, May 2, 2006.

Numerous arching red stems and a strong Selenium odor help identify Astragalus pattersonii, but a close look at the flower makes the identification more certain: Notice, in the two photographs below, the distinctive fringing of the calyx (the tube surrounding the base of the other floral parts).

Plants commonly grow 9 to 16 inches tall.

Asa Gray named this species from a specimen "collected by Mr. H. N. Patterson [in 1876?]... in the foothills of Gore Mountains, Colorado".  (Asa Gray's words as quoted in "T. S. Brandegee's 1876 "The Flora of Southwestern Colorado", part of the Hayden Survey Report.)   (More biographical information about Patterson.)

Astragalus pattersonii  (Patterson's Milkvetch)
Fabaceae (Pea Family)

Foothills. Openings. Spring, summer.
Mesa Verde National Park, May 2, 2006.

Spider-like fringing of the calyx, often arching leaves, and red stems are beautiful and diagnostic characteristics.

                   Astragalus pattersonii

Astragalus pattersonii

Astragalus pattersonii  (Patterson's Milkvetch)
Fabaceae (Pea Family)

Foothills. Openings. Spring, summer.
Mesa Verde National Park, May 9, 2008 and
Near Lone Mesa State Park, April 23, 2012.

Green seed pods form very soon after flower petals drop.  After the pods dry and split open spilling their seeds, they persist through the winter.

Range maps © 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 flavus

Range map for Astragalus pattersonii