An Illustrated Guide to ARIZONA WEEDS
The University of Arizona Press
NUTTALL MILKVETCH-Astragalus nuttallianus DC.
DESCRIPTION-A grayish slender annual, thinly covered with straight grayish hairs lying flat on the surface, reproducing only from seeds. The few weak stems are almost erect, and usually less than a foot high when growing with other plants. On barren soil they are prostrate, branch profusely, and radiate from a somewhat woody taproot, 1/2 to 3 1/2 feet in diameter, and often appear perennial. The leaves are divided into 3 to 6 (or 8) pairs of small narrow leaflets, the tips rounded, pointed, or with a slight notch.
The small pealike flowers are light purple, fading to nearly white, then drying blue. Two to 6 flowers (and later the pods) are clustered near the end of stiff threadlike stalks, 1 to 3 inches long. The stalks are solitary at the end of the stems and in the leaf axils.
The narrow flat pods, 1/2 to 3/4 inch long and 1/12 to l/8 inch long, curve upward, are hairy, or may be hairless, and slender-pointed at the top. They persist on the plant until they turn black. The tan colored flattened seeds are narrowly squarish, with a deep notch in one edge, and about 1/12 inch long.
DISTRIBUTION-Nuttall milkvetch is a native plant, and a common lawn pest, particularly in new lawns, yards, ditches, and fields. It is Arizona's most common annual Astragalus, and is abundant throughout the state on barren dry or disturbed soil along roadsides, waste places, river bottoms, mesas, slopes, and canyons in southern and northern desert, desert grassland, chaparral, and oak woodland ranges; 100 to 4,000 feet and infrequent to 7,000 feet elevation; flowering February to May, and sometimes again after the summer rains.
Copyright (c) 1972 The Arizona Board of Regents