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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 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.  Welsh's North American Species of Astragalus describes 354 species and 198 varieties. World-wide there are over 2,000 species. Intermountain Flora indicates, "The size and diversity of Astragalus has repeatedly suggested the division of the genus into more easily comprehensible, smaller, and more homogeneous units", but various attempts based on a host of characteristics have not succeeded in producing workable alternative genera.

   Keys that we do have to the Astragalus genus, are complex, running to many pages, and it is the seed pod, not the flower, that is  almost always crucial in identifying species. However, with patience and a good deal of assistance from a glossary, success can be had, and even if the exact species is not identified, the process is enlightening and the use of a hand lens in working through the key will make the beauty of the species so clear.

     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.     Some people use the common name "Locoweed" not only for Astragalus but also for another Pea genus, Oxytropis.  And, making common names even more confusing, many Astragalus are given 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). It's really not so hard to call them all "Astragalus". 

    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 coltonii

Astragalus coltonii variety moabensis

Astragalus coltonii

Astragalus coltonii

Astragalus coltonii

Astragalus coltonii
Astragalus coltonii  variety moabensis
Fabaceae (Pea Family)

Semi-desert, foothills. Woodlands, openings. Spring.
Upper Sand Canyon Trail, April 26, 2015, April 26, 2007, May 25, 2016, and April 30, 2016.

Astragalus coltonii can be very common in sandy, rocky areas at 5-7,000 feet in the Four Corners area of Utah and Colorado.  It occurs scattered through large areas, and also commonly can be in masses of plants. The plant seems especially sensitive to growing conditions: if it receives just what if likes in moisture and temperature, it grows and flowers profusely. If conditions are less than what it ideally wants, the plants will be far fewer with far fewer flowers.

In sunny areas, A. coltonii grows in an upright posture, but as shown below, it leans and stretches to greater heights in the shade.

Astragalus coltonii
Astragalus coltonii variety moabensis
Astragalus coltonii  variety moabensis
Fabaceae (Pea Family)
 

Semi-desert, foothills. Woodlands, openings. Spring.
Canyons of the Ancients National Monument, May 4, 2010.

In the winter of 2009-2010 snow was normal but the temperature was considerably below normal and snow melted slowly keeping the upper layer of soil moist for months. As the top two photographs on this page and the photograph at left give some evidence, this moisture provided phenomenal growth in Astragalus coltonii.  Trails were lined with thousands of lush plants.

Compare Astragalus coltonii with Astragalus wingatanus.

Astragalus coltonii  variety moabensis
Fabaceae (Pea Family)

Semi-desert, foothills. Woodlands, openings. Spring.
Canyons of the Ancients National Monument, April 26, 2007.

Dark hairs cover the buds and are scattered on the calyx.  Although the flowers are small, they are numerous and definitely attract attention, even in years of less than ideal growing conditions.

Marcus Jones collected this species near Castle Gate, Utah, named it for W. F. Colton of Moab, Utah, and described it in 1891.  Alice Eastwood collected this variety near Monticello, Utah, in 1892 and Jones named and described it in 1898.

Astragalus coltonii variety moabensis
Astragalus coltonii  variety moabensis
Fabaceae (Pea Family)
 

Semi-desert, foothills. Woodlands, openings. Spring.
Canyons of the Ancients National Monument, May 20, 2010.

Pods are glabrous (smooth), about an inch long, and varyingly red-tinged or mottled.

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 coltonii