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MARSH SOWTHISTLE - Sonchus arvensis L. ssp. uliginosus (Bieh.) Nyman

Asteraceae - (Sunflower family)

This perennial arising from an extensive creeping root system is commonly 1 to 6 feet tall, glabrous, at least below the inflorescence and often covered with a waxy film which can be rubbed off. Herbage has a milky juice. Leaves are prickly-margined, the lower and middle ones are usually pinnately lobed to pinnatifid, mostly 4 to 10 inches long and 1 to 1 1/2 inches wide. Upper leaves are progressively less lobed and become clasping, uppermost leaves bractlike. Flowering heads, 1 to 1 1/2 inches across at anthesis, grow in a terminal flat to a domelike cluster. It has yellow ray flowers, which are fertile. Achenes are flattened, ribbed and rugose, with pappus of capillary bristles.

Marsh sowthistle was introduced from Europe and is a creeping perennial. Marsh sowthistle (listed by various authors as S. uliginosus or S. glabrescens) lacks gland-tipped hairs.

(Courtesy of Weeds of the West)