annual sowthistle
Family
AsteraceaeScientific Name
Sonchus oleraceusOther Common Names:
annual sow thistle
hare's colwort
hare's thistle
milky tassel
smooth sow thistle
sow thistle
swinies
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.
Roots: Taproot.
Stems: Unbranched, 1-4 ft in height, and emit a milky sap when cut.
Identifying Characteristics
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.
Seed Fruit
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.
Where Found
Found throughout the United States.
Growth Habit
upright and nonwoody
Thorns or Spines
present
Approximate Flower Diameter
Varies:
pencil,
dime,
nickle
Dominant Flower Color
Varies:
white,
yellow
Flower Symmetry
radial symmetery
Leaf Hairs
no hairs
Leaf Shape
oval
Leaf Arrangement
Varies:
alternate,
rosette
Leaf Margin
Varies:
entire,
lobed,
serrated
Leaf Structure
simple
Leaf Stalk
none
Stem Hairs
no hairs
Stem Cross Section
round or oval
Milky Sap
present
Root Structure
Varies:
fibrous,
taproot
Life Cycle
winter annual
Ochrea
not present
Plant Type
Herb