Annual Sowthistle: Sonchus oleraceus
||Weed Description: An annual
with bluish-green leaves and stems that secretes a milky sap when cut. Found throughout
the United States.
egg-shaped and have petioles. Young leaves are alternate, egg-shaped, and form a rosette.
Both young leaves and cotyledons have a whitish coating.
|Leaves: 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.
Stems: Unbranched, 1-4 ft in height, and emit a milky sap
|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.
|Identifying Characteristics: The
leaves with very prickly margins that initially develop as a basal rosette and then occur
alternately along the flowering stem, the bluish-green color of the leaves, 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.