Lactuca Virosa generally an annual, although an occasional biennial, wild lettuce grows to a maximum height of six feet and has a pale green central stalk that is sometimes spotted with purple. The erect stem, springing from a brown tap-root, is smooth and pale green, sometimes spotted with purple. There are a few prickles on the lower part and short horizontal branches above. The numerous, large, radical leaves are from 6 to 18 inches long, entire, and obovate-oblong. The stem leaves are scanty, alternate, and small, clasping the stem with two small lobes. The heads are numerous and shortly-stalked, and the pale-yellow corolla are strap-shaped. The rough, black fruit is oval, with a broad wing along the edge, and prolonged above into a long, white beak carrying silvery tufts of hair. The whole plant is rich in a milky latex that flows freely from any laceration. This latex has a bitter taste and a narcotic odour. When dry, it hardens, turns brown, and is known as lactucarium.
Lactusa virosa is ofetn confused with Lactusa serriola, as the two plants may appear very similar. When bruised, however, Lactusa virosa exhibits a smell very similar to that of opium poppy. Furthermore, fresh Lactusa virosa achenes are very purple or maroon in color.
Lactuca virosa - Wild Lettuce, Lettuce Opium - Entheology.com, http://entheology.com/plants/lactuca-virosa-wild-lettuce-opium/ (accessed January 19, 2017).