Coarse, spiny plant, to 4 ft tall. Stems spiny. Leaves curving, deeply lobed, with numerous spiny teeth. Leaf bases clasp the stem (bottom left). Flower heads about 1 and 1/2 to 2 inches wide, disk flowers bright yellow. Blooms in summer.
A noxious weed from Eurasia. Prefers open, disturbed areas such as farmland, pasture, fields and roadsides. Occasional in Wildwood along the Bikeway and in meadows.
Two other weedy sow thistle are possible in the Park, although they have not been reported. Spiny-leaved sow thistle (S. asper) has leaves with longer spines, and the leaves are usually not lobed. Common sow thistle (S. oleraceus) has lobed leaves that have very large triangular terminal lobes. Both have smaller, paler flowers than field sow thistle.
Despite the spines it is quite nutritious and eaten by wild and domestic animals and even humans.