Semi-desert.  Open shrub and grasslands and woodland openings.  Spring.

This is a very common annual Astragalus in the lower areas of the Four Corners region, often carpeting the ground.  It is highly variable in form, ranging from the tiny, prostrate plant pictured 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 flower 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 for Nuttall in 1825.  (Quotation from Intermountain Flora.)