An Illustrated Guide to ARIZONA WEEDS

The University of Arizona Press

WOOTON LOCO, western loco, locoweed, rattleweed


PEA FAMILY-Leguminosae

WOOTON LOCO-Astragalus wootonii Sheldon

DESCRIPTION-A rank, spreading annual, biennial, or shortlived perennial from a thick taproot, reproducing by seeds. The weak stems are branched from the base, erect and bushy at first, but sprawling on the ground in age, usually not over 1 foot long, and mostly less. The leaves are divided into 4 to 11 pairs of small narrow grayish leaflets, 1/12 to l/8 inch broad, with inconspicuous straight hairs Iying on the surface.

The pealike flowers are reddish purple, fading paler, and only l/4 to 1/3 inch long. The flower stalks, 1 to 2 1/2 inches long, arise in the leaf axils, bear about 5 to 10 flowers, and usually do not extend beyond the leaves. The yellowish thin walled pods are papery, and greatly inflated when mature. They are nearly straight along 1 edge, strongly curved on the other, 5/8 to 1 1/8 inches long. The reddish brown, flattened seeds are broadly kidneyshaped, about l/8 inch long, and have a notch on 1 edge.

DISTRIBUTION-Wooton loco is a very common native plant, growing mostly on dry sandy soil along roadsides, mesas, plains, slopes, and washes throughout the state. In wet springs it often covers large areas (e.g. between Window Rock and Holbrook), in both northern and southern desert, desert grassland, and sometimes oak woodland ranges; from 1,300 to 7,000 feet elevation; flowering March to May or June, and sometimes again in August.

POISONOUS PROPERTIES-Wooton loco is definitely known to cause loco poisoning in livestock. Animals do not like it, and usually will not eat it except when hungry for green feed, or after they are addicted to locoweed. It is poisonous even in the dry state.

HALFMOON LOCO-Astragalus allochrous Gray

DESCRIPTION-Halfmoon loco is also known to be poisonous. It is often con- fused with Wooton loco, and has the same geographical and habitat distribution. The stems are 1 to 2 feet long, the leaves have 11 to 19 pairs of leaflets, 1/12 to 1/3 inch broad, and the pods are larger and more conspicuous, 1 1/8 to 1 3/4 inches long.

Copyright (c) 1972 The Arizona Board of Regents

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