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Ministry of Agriculture, Food and Rural Affairs

ANNUAL SOW THISTLE

Scientific Name: Sonchus oleraceus L.

Other Names: Laiteron potager, Common annual sow-thistle, laiteron lisse, laiteron commun.

Family: Composite or Aster Family (Compositae)

General Description: Very similar to spiny annual sow-thistle in general appearance. Annual, reproducing only be seed. Whole plant with sticky white juice.

Habitat: It occurs in habitats similar to those of spiny annual sow-thistle. Occurs throughout Ontario in waste places, along fence lines, roadsides, around buildings and occasionally in gardens.

Seedlings

Stems

  • Erect,
  • 40 cm -1 m in height.

Leaves

  • The part closer to the stem very narrow,
  • The base clasping the stem with 2 angular or pointed lobes,
  • All margins with small teeth and soft weak spines.

Flowers

  • Yellow,
  • Small (2 cm in diameter),
  • On stalks at the end of the stems.

Seeds

  • Ridged lengthwise,
  • Each ridge with numerous small cross-wrinkles.

Often Confused With
Easily distinguished by having leaves which are deeply lobed with the terminal lobe being short, broad and rounded or triangular.

Annual sow thistle Annual sow thistle Annual sow thistleClick to enlarge.