Scientific NameSonchus oleraceus
Other Common Names:
annual sow thistle
smooth sow thistle
Rosette leaves alternate, egg-shaped, with toothed margins. Stem leaves are alternate, without hairs, and have lobes that clasp the stem. Leaf margins are toothed and only slightly prickly. Roots: Taproot. Stems: Unbranched, 1-4 ft in height, and emit a milky sap when cut.
An annual with bluish-green leaves and stems that secretes a milky sap when cut. The bluish-green color of the leaves, the very prickly margins of the leaves that initially develop as a basal rosette and then occur alternately along the flowering stem, and the yellow flowers with a 'puff-ball' seedhead are all characteristics that help in the identification of annual sowthistle. Spiny Sowthistle (Sonchus asper) is very similar in appearance, however this species has rounded lobes that clasp the stem whereas annual sowthistle has distinctly pointed lobes. Also, the leaf margins of spiny sowthistle are much more spiny or prickly than those of annual sowthistle. Both of the sowthistles can be distinguished from 'true' thistles by the milky sap they emit when broken. The sowthistles might also be confused with Prickly Lettuce (Lactuca serriola), however the midvein on the leaf undersides of this weed has distinct spines or prickles, whereas those of the sowthistles do not.
Flower Seed Head
Flowers: Several occur in clusters at the end of the stems, pale yellow, 1/4 to 3/4 inch wide.
Fruit: An achene. Mature seed have a white feathery pappus that collectively form a white "puff ball" similar to dandelion. Seedling: Cotyledons egg-shaped and have petioles. Young leaves are alternate, egg-shaped, and form a rosette. Both young leaves and cotyledons have a whitish coating.
Found throughout the United States.
upright and nonwoody
Thorns or Spines
Approximate Flower Diameter
Dominant Flower Color
Stem Cross Section
round or oval