annual sowthistle

Family

Asteraceae

Scientific Name

Sonchus oleraceus

Other Common Names:

hare's thistle

swinies

milky tassel

hare's colwort

annual sow thistle

sow thistle

smooth sow thistle

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