Scientific Name: Sonchus arvensis

Common Name: perennial sowthistle

Other Common Names: field sowthistle, corn sowthistle, gutweed swine sowthistle

Habit: Seedlings have 0.2-0.3 inches long by 0.1-0.2 inches wide, ovate cotyledons. Mature plants have a vast horizontal root system and hollow, succulent, branching stems reaching 7 ft tall.

Leaves: Found mostly on the lower half of the stem, leaves are lance-shaped 2.5-16 in long and alternate in arrangement. Lower leaves have winged curled back stalks and are deeply lobed with soft prickly margins. Stalkless upper leaves clasp the stem and have 2-7 backward pointing lobes on each side. Margins of upper leaves are not as deeply lobed but they have teeth tipped with spines.

Identifying Characteristics: Yellow flower heads measuring more than 1 in across, stems below and flower bracts covered with yellow hairs and milky juice in stems and leaves. Even small numbers of plants can severely reduce crop yields due to its ability to compete for light, space, nutrients, and moisture.

Flower Seed Head: Each plant bears several flower heads made up of bright yellow ray florets and dark-green floral bracts. Stems below flower heads and floral bracts are covered with yellow hairs.

Seed Fruit: A single seeded achene. The seeds 3.0 mm long and less than 1 mm wide are reddish brown, and rectangular. Each plant is capable of producing 4,000 seeds that may remain viable in the soil for several years. Dispersal is aided by the pappus made up of several 0.4-0.5 in long white hairs.

Where Found: Throughout Canada and the United States in cultivated crops, pastures, and meadows.

  • Life cycle: perennial

  • Milky sap: Present

  • Plant type: Herb

  • Thorns: Present

  • Plant family: Asteraceae

  • Leaf arrangement: alternate; rosette

  • Leaf shape: lance; oval

  • Ochrea: Not Present

  • Leaf margin: serrated; lobed

  • Stem hairs: has hairs; no hairs

  • Flower color: yellow; orange

  • Growth habit: upright and nonwoody

  • Stem: round or oval

  • Leaf structure: simple

  • Leaf hairs: no hairs; has hairs

  • Flower diameter: quarter; larger; half dollar

  • Flower symmetry: radial symetery

  • Root structure: taproot

  • Leaf stalk: shorter than leaf; none