An Illustrated Guide to ARIZONA WEEDS
The University of Arizona Press
ANNUAL SOWTHISTLE-Sonchus oleraceus L.
DESCRIPTION-Tall fleshy annual, very similar to spiny sowthistle, but the achenes and leaves are different. The leaves are very thin, and all1 (except some uppermost) are deeply-lobed. In the most common form, the principal leaves are deeply cut into 1 to 3 lobes along each side, with the tip-lobe much larger and broadly triangular; or sometimes without side lobes, but just one large lobe at the tip, and a long narrow winged stalk. Unfortunately, the other common leaf form is similar to the many (5 to 7) lobed leaf of spiny sowthistle, with the tip lobe no larger than the side lobes. However, there is one consistent leaf characteristic-the pair of projections at the base of the stalkless, clasping leaves are sharp-pointed or taper to a point, and are not rounded and earlike as in spiny sowthistle.
The flower heads are slightly larger in annual sowthistle, about 3/4 to 1 1/4 inches broad. No gland-tipped hairs are found in any parts of the plant. The achenes are about the same length, 1/12 to 1/8 inch, but are 3 1/2 to 4 times as long as broad, with the broadest part near the top. There are 5 to 7 indistinct ribs on each face, with roughened, cross-wrinkling in the furrows between them. The edges are not thin nor wing-margined, but as thick as the body. The difference between the achenes are best seen with a hand lens.
DISTRIBUTION-Annual sowthistle is native of North Africa, Europe, and western Asia. Found throughout most of Arizona, but not as abundant as spiny sowthistle, and not a serious pest in winter croplands. Growing in vacant lots, roadsides, and uncultivated grounds as well as cultivated fields, gardens, bottomlands, and ditchbanks. The young leaves of both this plant and spiny sowthistle were gathered in the spring and cooked as greens, but probably an uncommon practice in modern Arizona. Found from 150 to 7,000 feet elevation; flowering February to November.
Copyright (c) 1972 The Arizona Board of Regents