Common Australian Garden Weeds

Sonchus oleraceus

Scientific name: Sonchus oleraceus L.


Habit of milk thistle (Sonchus oleraceus).


Flower-heads of milk thistle at various stages of development.


Close-up of one of the constricted flower-heads.


Mature fruit of milk thistle with many wind-blown seeds prior to dispersal.


A milk thistle seedling.


Young milk thistle plant with irregularly toothed leaves.

Common name: Common sowthistle, milk thistle.

Family: Asteraceae

Origin:

Native of Europe and northern Africa.

Habit:

Annual herb with a thick, erect stem up to 1 m tall.

Habitat:

Common weed of disturbed ground.

General description:

Stems and leaves
The hollow stems exude a white sap if broken. The soft leaves are bluish green, with irregularly toothed margins. the base of the leaf extends to clasp the stem. The size of the leaves is greatest at the base of the plant and reduces upwards. The larger leaves may be up to 20 cm x 10 cm in size.
Flowers and fruit
Flower-heads are bright yellow and up to 2 cm across when open. They are borne in clusters at the tips of the upright stems. Flowering occurs over most of the year. Seeds are narrow, ribbed lengthwise and 3 mm long with a 6-7 mm long white silky tuft of hairs (pappus) at one end.

Distinguishing features:

Annual herb growing up to 1 m tall with irregularly saw-toothed leaves with milky sap (latex) and yellow 'thistle' flowers (2 cm across) that are borne in clusters at the tips of a branched erect stem.

Noxious status:

No noxious.

Sources:

Kleinschmidt, H.E., Holland, A. and Simpson, P. (1996). Suburban Weeds. 3rd Edition. Department of Primary Industries, Brisbane.

Stanley, T.E. and Ross, E.M. (1983-1989). Flora of South-eastern Queensland. Volume 2. Department of Primary Industries, Brisbane.

Auld, B.A. and Medd, R.W. (1996). Weeds: An Illustrated Guide to the Weeds of Australia. Inkata Press, Sydney.