An Illustrated Guide to ARIZONA WEEDS

The University of Arizona Press

RUBBER RABBITBRUSH,big rabbitbrush

Illustration

SUNFLOWER FAMILY-Compositae

RUBBER RABBITBRUSH-Chrysothamnus nauseosus (Pallas)Britt.

DESCRIPTION-Large woody shrubs, 1 1/2 to 6 feet high with numerous shreddy- barked, flexible trunks from the base. The many young branches and stems arising annually from these are covered by a dense feltlike coat of white to dull white to yellowish wool. These are somewhat sticky due to a resinous gum which gives the plant a characteristic odor. The narrow, alternate leaves, 1 to 3 inches long, less than 1/3 inch broad, are smooth-margined and covered when young by the same feltlike coat of wool.

The small, narrowly coneshaped flower heads, about1/4 to 1/2 inch high, are in rounded clusters at the ends of the stems. The firm, pointed bracts surrounding each flower head have a resinous-thickened center, and are arranged in 3 to 5 vertical rows. Each flower head contains only 4 to 6 tiny yellow tubular flowers, the tube about 1/4 to ]/2 inch long. Outer ray flowers are lacking in these heads. The slender achenes are angled, and vary from smooth to densely hairy. Each bears a tuft of dull white hairs of unequal length at the top.

There are nine different varieties of rubber rabbitbrush in Arizona. They show great variability in the density of hairs, the shape, and the length of leaves, achenes, and bracts surrounding the flower heads.

DISTRIBUTION-Rubber rabbitbrush is a native weed of deteriorated rangelands. It often grows in dense stands, replacing good forage grasses which have been killed out by overgrazing. Found along roadsides, waste places, or in dry washes, plains, foothills, and bottomlands of mountain valleys. It thrives in alkali and heavy clay, or in sandy, gravelly soil; in sagebrush, pinyon-juniper, and ponderosa pine zones.

Spread throughout Arizona in one or more of its forms, except in the western and southwestern portions; from 2,000 to 8,000 feet elevation; flowering from July to November. Of little forage value to livestock, and unpalatable because of its resinous substances.

POISONOUS PROPERTIES-Although poisonous to livestock, the plant is not eaten in large enough quantities to cause losses.

Copyright (c) 1972 The Arizona Board of Regents



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