An Illustrated Guide to ARIZONA WEEDS

The University of Arizona Press

WESTERN WHORLED MlLKWEED,horsetail milkweed, poison milkweed


MILKWEED FAMILY-Asclepiadaceae

WESTERN WHORLED MILKWEED-Asclepias subverticillata (Gray) Vail (A. galioides of authors, not H.B.K.)

DESCRIPTION-An erect bushy, hairless perennial with milky juice, which reproduces by seeds and by wiry, creeping roots. There are many slender unbranched stems 1 to 4 feet high, arising close together from the horizontal roots, giving large plants a shrubby appearance. Three (sometimes 2 or 4) long narrow leaves are found in whorls at each stem joint. These are 3 to 5 inches long, nearly stalkless, not over 1/3 inch broad and usually less, with the edges slightly rolled backwards.

The small, greenish white flowers occur in umbrellalike clusters at the top of the branches, and in the leaf axils. The slender seedpods, 2 to 4 inches long, splindleshaped and long pointed, with erect stalks, contain many seeds. The flat brown seeds, 1/4 inch long, have corky margins and a tuft of silky hairs at the tip. They are similar to those of broadleaf milkweed, but slightly smaller.

DISTRIBUTION-Western whorled milkweed is native in western United States and Mexico. It grows in dryish soil along roadsides, edges of fields, and pastures, ditchbanks, plains, mesas, and slopes. Found throughout most of the state on practically all types of ranges from desert to spruce fir, it is probably most common in yellow pine; 2,500 to 8,500 feet elevation; flowering May to September.

POISONOUS PROPERTIES-All parts of western whorled milkweed above the ground are poisonous at all times, even when dried. It is poisonous to all classes of livestock, but particularly to sheep. None of the milkweeds are palatable to livestock, and animals will rarely touch them if other forage is available.

Copyright (c) 1972 The Arizona Board of Regents

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