Southwest Colorado Wildflowers, Astragalus 2

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 praelongus (Stinking Milkvetch)
Fabaceae (Pea Family)

Semi-desert. Shrublands, openings. Spring.
BLM lands near the San Juan River, Utah, April 6, 2005.

Astragalus praelongus has long, tubular, light yellow flowers in thick dangling clusters. Last year's seed pods (curled, sharp-tipped, and split open) project in all directions. Stems are tall and light green and leaflets are numerous. The plant overall is quite robust and shrub-like with masses of flowers followed by masses of seed pods.

The plant often grows on Selenium rich soils and picks up the characteristic Selenium fetid odor, thus the common name, "Stinking Milkvetch". Beware! Touching this plant releases a really unpleasant Selenium stink. (See the very similar-stinking Astragalus pattersonii.)

"Prae, longus", the Latin, "before, long" perhaps refers to the crowded young flowers soon becoming spaced out as the flower stem elongates.

Astragalus praelongus

Astragalus praelongus (Stinking Milkvetch)
Fabaceae (Pea Family)

Semi-desert. Shrublands, openings. Spring.
BLM lands near the San Juan River, Utah, April 6, 2005.
Bisti/De-Na-Zin Wilderness Area, New Mexico, May 21, 2009.

Flower banners are smoothly arched back and sides of the banners are rolled upward and inward. Wings are quite long and the keel (barely visible at the bottom center of the second photograph) is often lilac tipped.

Two varieties of Astragalus praelongus are shown in the four photographs. The top two photographs show Astragalus praelongus variety ellisiae with longer and fewer leaflets and narrow and long pods. The bottom two photographs show variety praelongus with shorter and more numerous leaflets and plump, shorter pods.

Astragalus praelongus (Stinking Milkvetch)
Fabaceae (Pea Family)

Semi-desert. Shrublands, openings. Spring.
Bisti/De-Na-Zin Wilderness Area, New Mexico, May 21, 2009.

Notice, along the right side of the photograph, the straw-colored, thick stems and buffy, dried seed pods from last year's growth. These characteristics assist in identifying Astragalus praelongus.

The pods on the variety of Astragalus praelongus shown at left and immediately above are shorter and fatter than the pods of the variety shown in the Astragalus praelongus in the first two photographs.

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 praelongus