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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, 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. |
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Astragalus
coltonii variety moabensis Fabaceae (Pea Family) Semi-desert, foothills. Woodlands, openings. Spring. 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 often occurs scattered through large areas, but rarely in masses of plants. It grows in an upright posture, but as shown below, leans and stretches to greater heights in the shade.
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Astragalus
coltonii variety moabensis Fabaceae (Pea Family) Semi-desert, foothills. Woodlands, openings. Spring. 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. |
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Astragalus
coltonii variety moabensis Fabaceae (Pea Family) Semi-desert, foothills. Woodlands, openings. Spring. 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 (near Castle Gate, Utah), named (for W. F. Colton of Moab, Utah), and described Astragalus coltonii in 1891. Alice Eastwood collected this variety near Monticello, Utah, in 1892 and Jones named and described it in 1898. |
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Astragalus
coltonii variety moabensis Fabaceae (Pea Family) Semi-desert, foothills. Woodlands, openings. Spring. Pods are glabrous (smooth), about an inch long, and varyingly red-tinged or mottled. |
Range map © John Kartesz,
County Color Key
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Range map for Astragalus coltonii |
Species present in state and native
Species present in state and exotic
Species not present in state
Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Questionable presence