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.

Semi-desert.  Woodlands, openings.  Spring.
Canyons of the Ancients National Monument, April 20, 2007 and April 8 and May 3, 2010.

This is a rare species found just in a few counties in the Four Corners region.  It grows in sand islands on rock expanses and in other sandy areas.  Flowers have delicately lavender streaked banners and intensely purple wings.  In shady areas with normal moisture (top photograph at left), it is often sparsely leaved, but in sunny areas following winters of continual moisture, it can be robust. 

Semi-desert.  Woodlands, openings.  Spring.
Canyons of the Ancients National Monument, April 20, 2007.

Astragalus naturitensis faded flowers give no indication of past beauty.  Astragalus naturitensis seed pods are compressed, mottled, short-haired, and straight-to-moderately curved.

A. naturitensis is very similar to A. monumentalis which is found in similar habitats and has a similar very limited distribution only in the Four Corners. Descriptions of the two plants given by expert botanists do not, however, agree on numerous characteristics and it is, therefore, very difficult or impossible to know which species one is looking at.  As an example of the confusion: Weber indicates that the seed pod of A. naturitensis is "essentially straight" and the pod of A. monumentalis is "strongly incurved" ; Welsh indicates that the pod of A. naturitensis is "incurved" and that of A. monumentalis is "straight or curved"; Cronquist indicates that A. naturitensis is "gently incurved" and A. monumentalis is "when relatively short only a trifle incurved, when longer often but not consistently falcately incurved [sickle-like]".

In 1892 Alice Eastwood collected this beautiful plant west of Cortez in McElmo Canyon (perhaps in the very area these photographs were taken 115 years later).  In 1895 Marcus Jones named the plant Astragalus arientinus and then Astragalus stipularis but the names were ruled "nomen nudum", i.e., they were ruled "naked names", not accompanied by proper descriptions of the plant and, therefore, not accepted as the name.  In about 1915, Edwin Payson found the plant near Naturita, Colorado, and properly published a description with the name Astragalus naturitensis.

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

This is a very common Astragalus in the lower elevations of the Four Corners region, often carpeting the ground.  It is highly variable in form, ranging from the tiny, prostrate plant pictured at left to plants a foot tall covered with flowers.  Leaflets range from 7 to 15  and flowers from 1 to 7 per cluster. A close look reveals a beautifully multi-colored, tiny flower (about one-third inch long) with a tall, spreading banner.

Thomas Nuttall -- teacher, collector, taxonomist -- was a giant of 19th century botany.  He collected the first specimen of this plant "On the plains of the [Arkansas] River" and named it Astragalus micranthus in 1821. Augustin de Condole renamed it to honor Nuttall in 1825.  (Quotation from Intermountain Flora.) (More biographical information.)

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
Eradicated
Questionable presence

Range map for Astragalus naturitensis

Range map for Astragalus nuttallianus