Southwest Colorado Wildflowers, Astragalus amphioxys and chamaeleuce

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.

Pods are an inch+, hairy, often on
the ground, and sometimes curved
in almost a circle.

Astragalus amphioxys
Fabaceae (Pea Family)

Semi-desert. Openings. Spring.
Negro Bill Canyon Trail, Utah, April 12, 2005.
Canyons of the Ancients National Monument, April, 15, 2007.

Astragalus amphioxys has a light green, hairy, arching leaflet

and attractive, magenta/purple flowers. The upright banner is gently cupped, enfolding a light center.

Flowers fade to light purples and steel grays and the inflated seed pods that follow are sharply narrowed and compressed on both ends, giving rise to the scientific name: the Greek "amphi", "on both ends" and "oxys", "sharp".

Astragalus chamaeleuce
Fabaceae (Pea Family)

Semi-desert. Openings. Spring.
Canyons of the Ancients National Monument, April 5, 2005.

This Astragalus shouts out at you with large, deep magenta flowers. You'll hear it on hot, dry hillsides early in the spring. Astragalus chamaeleuce grows in sprawling low mats of light green leaves topped by numerous clusters of flowers. The upright banner of the flower curves backward slightly

and the two forward thrusting wings (bottom right in the above picture) are long, straight, and narrow, gently enfolding the vertical keel. Seed pods are swollen and often almost spherical but tapered to a sharp prow-like point on one end.

"Chamae" is Greek for "on the ground" and "leuc" is Greek for "white"; perhaps these refer to the light color of the leaves and the sprawling growth pattern.

Astragalus chamaeleuce
Fabaceae (Pea Family)

Semi-desert. Openings. Spring.
Canyons of the Ancients National Monument, March 27, 2005.