Common Sow-thistle

Family: Daisy (Asteraceae syn. Compositae)

Scientific Name:

Sonchus oleraceus

Common Sow-thistle plant
Photo: A J Brown

Other Common Names:

Sow Thistle, Smooth Sow-thistle, Annual Sow-thistle, Swinies, Soft Thistle, Hare’s Thistle, Hare’s Lettuce, Hare’s Colwort, Colewort, Milk Thistle, Common Milk Sow-thistle, Milky Tassel, Milk-weed, Thalaak

Status:

Native to Europe and south-west Asia. Naturalised throughout Australia and New Zealand.

Plant Description:

Annual to 140 cm tall with a basal rosette of leaves as well as leaves along the stems. Stems and main vein of leaves are dark-green to purple. Leaves are thin and soft, up to 35 cm long and 12 cm wide, lanceolate (lance-shaped) to oblanceolate (pointed end attached to the stem), hairless and are dark green with pale white to purple veins. Leaves are moderately to deeply lobed with the terminal lobe often the largest and the base of stem leaves have pointed, ear-shaped lobes (auricles). Leaf margins are irregularly toothed but not spiny.

Flower stems and involucre (flower cup) are hairless or have gland-based hairs. Involucre 10-13 mm long and ‘petals’ (each is actually a single flower) are 5-6 mm long and yellow and usually only open during the mornings of each day. The fruit is a cypsela or achene (dry, indehiscent and one-seeded), obovoid 2.5-4 mm long, moderately compressed, tapering at the base, wrinkled all over and 3-ribbed on each face.

Habitat:

Very common weed of disturbed areas, gardens and waste places throughout Victoria. Also found on swamps, lake edges and coastal dunes and provided moisture is adequate, appears to have some tolerance to slightly saline conditions.

Region	Salinity Class	Waterlogging Class
Mallee, Loddon Murray	S0, S1	W1, W2, W3
Central and Northern, Wimmera, Western, Gippsland	S0, S1	W0, W1, W2, W3

Comments:

Common names refer to the attractiveness of the plant to hares, rabbits and pigs. Common Sow-thistle can differ in leaf shape and overall appearance. Some authorities believe that populations of Clammy Sow-thistle (Sochus tenerrimus) found in Australia are actually one of these forms of Common Sow-thistle.Common Sow-thistle belongs to a group of mainly yellow-flowered daisies in the Tribe Lactuceae. The plants in this tribe are characterised by having a basal rosette of leaves (flat-weeds), milky sap in their stems and their flower-heads consisting entirely of ray florets (i.e. no ‘eye’ to the daisy). See Key to Yellow Daisy Flat-weeds.

Common Sow-thistle Photos

Common Sow-thistle growing in waste garden place Photo: A J Brown	Leaf auricles of Common Sow-thistle Photo: A J Brown
Opening flower buds of Common Sow-thistle Photo: A J Brown	Flower of Common Sow-thistle Photo: A J Brown
Leaf margin of Common Sow-thistle Photo: A J Brown

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