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(milk thistle), a genus of plants of the family Compositae. The plants are biennial or perennial herbs reaching 1.5 m in height. The leaves are alternate, large, white-spotted, pinnately lobed, and spinose-toothed. The flowers, which are tubular, bisexual, and usually purple, are large (3–6 cm across) and in solitary heads. The fruit is a compressed achene with a pappus of rough, white bristles. There are two species, distributed in Europe, the Caucasus, Asia Minor, Southwest and Middle Asia, and North Africa. The USSR has one species, the blessed thistle (S. marianum), which grows along roads and fields, on fallow land, in gardens, and near dwellings. The plant is sometimes raised as an ornamental. The fruits contain an edible oil.