An Illustrated Guide to ARIZONA WEEDS

The University of Arizona Press

SPINY ASTER, Mexican devilweed



SPINY ASTER-Aster spinosus Benth.

DESCRIPTION-Grayish, much branched perennial, nearly leafless, 2 to 9 feet high, reproducing by seeds and by widespreading creeping rhizomes. The intricately branched grayish stems are hairless, longitudinally ribbed, woody below, with few to many very stout, stiff, sharp, greenish spines, 1/8 to 1 inch long, borne in or above the axils of the upper leaves.

The upper leaves are scarce, scalelike but green, and soon fall off. The lower leaves, also scarce, are very slender, 1/4 to 2 1/2 inches long. The flower heads are 1/3 to 1/2 inch high, and 1/2 to 3/4 inch across, including the many narrow white "petals" (ray flowers); the center of the head is yellow or brownish.

The flower heads are many to numerous, stalked, and borne at the top of the plant on branching flowering stems, or sometimes they are solitary at the end of a branchlet. The reddish brown achenes, 1/16 to 1/12 inch long, are narrowly oblong, hairless, longitudinally ribbed, with a tuft of fine hairs at one end.

DISTRIBUTION-Spiny aster is a native plant, commonly forming rank, hedgelike thickets along the banks of irrigation ditches. In some agricultural areas, it infests cultivated crops, especially soybean, cotton, alfalfa or small grain fields, as in the Yuma Valley. Also a common pest in heavy, more or less alkaline valley soils, or in moist saline soil along river bottoms, pastures, and low places. Found throughout the state in the deserts; 100 to about 4,500 feet elevation; flowering April to October, but principally in the summer and fall.

Copyright (c) 1972 The Arizona Board of Regents

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