Perennial sowthistle

Sonchus arvensis L. Asteraceae (Aster family)

Life cycle

Erect, patchforming perennial.

Perennial sowthistle
Perennial sowthistle plant.

Leaves

Seedling leaves initially develop from a basal rosette from a deep taproot. Lower leaves are alternate, bluegreen, 4 to 12 inches long with two to five lobes with prickly teeth on each side, gradually becoming smaller toward the top with a clasping base. Leaves have a thickened midvein and exude a milky sap when damaged. Leaf midvein is not prickly underneath.

lower leaf of perennial sowthistle
Lower leaf of perennial sowthistle.

Clasping leaf base of perennial sowthistle
Clasping leaf base of perennial sowthistle.

Stems

Erect, herbaceous stem up to 5 feet tall that branches only near the flowers. Stems are hollow and smooth with ridges and exude a milky sap when damaged. Upper stems may have gland-tipped hairs.

Milky sap of perennial sowthistle.
Milky sap of perennial sowthistle.


Perennial sowthistle flower
Perennial sowthistle flower.

Flowers and fruit

Bright yellow ray flowers are 1 to 2 inches wide and found in clustered heads. The seed is enclosed in a singleseeded, narrow, oval, reddish brown, ribbed, wind-disseminated fruit.

Reproduction

Seeds and extensive creeping roots.

Similar weeds

  • Annual sowthistle (S. oleraceus L.) Differs by having an annual life cycle and a short taproot, less prickly leaf margins, and pale yellow, .5- to 1-inch-wide flower heads. Leaf midvein is not prickly underneath.
  • Prickly lettuce (Lactuca serriola L.) Differs by having an annual or biennial life cycle; fine prickles on leaf margins and sharp prickles on the underside of the leaf midvein; and a many branched, spreading panicle with numerous pale yellow flower heads less than .5 inch wide.
  • Spiny sowthistle (S. asper [L.] Hill) Differs by having an annual life cycle and short taproot, leaf margins with many sharp prickles, earlike lobes where the leaf attaches to the stem, and flower heads .5 to 1 inch wide. Leaf midvein is not prickly underneath.

sharp prickles prickly lettuce rosette spiny sowthistle leaf
Sharp prickles on the underside of the leaf midvein of prickly lettuce (left). Prickly lettuce rosette (middle). Spiny sowthistle leaf (right).

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