Sonchus oleraceus

sow thistle


Sonchus oleraceus

L. 1753

pronounced: SON-kuss awl-ur-RAY-see-us

(Asteraceae — the daisy family)


common names: sow thistle, milk thistle

Sonchus is from the Greek word σονχος (sonchos), used by botanists for the sow-thistle; oleraceus is a Latin adjective meaning ‘vegetable’.

This thistle, introduced from Europe, is an annual that emerges, grows and flowers at any time of the year, and is particularly abundant in winter and spring. It is widespread and common, and a serious crop weed in some places. It does not usually persist in pasture, as it is readily grazed. It is moderately salt-tolerant (the plants photographed were in the Picnic Bay Mall, on the seaward side of the path), and is widely naturalized throughout the world.

Sow Thistle grows to a height of 30–110 cm, occasionally higher, has hollow stems, and exudes latex if damaged. It is due to the latex that the plants obtained the common name, ‘sow thistle’, as they were fed to lactating sows in the belief that milk production would increase. Habitats include most soil types, fields, pastures, roadsides, gardens, vacant lots, construction sites, and waste places.

The plant develops a deep tap-root. The hollow stems are 5-angled, and a dark green that is sometimes tinged with reddish purple. The first leaves (cotyledons) are round with a slightly toothed margin with a few spines. They have sparse hairs on the upper leaf surface. The mature leaves are thin with irregularly-toothed margins, ending in small soft spines. They become increasingly lobed with maturity. The leaves clasp the stem, except at the base. The lower stem leaves can be up to 25 cm long. They have pale white to pale purple veins, and they form a rosette at the base of the plant, often lying flat against the ground.

The flower heads are yellow. 5 – 6 mm in diameter, and are borne on stalks at the ends of branches in an irregular terminal panicle, with or without hairs. The flowers tend to open between about 6:00 AM and 11:00 AM.

The fruit is an achene 2.5 –  4 mm long and 1 mm wide, brown, 3-ribbed on each face, wrinkled with narrow margins, flattened and obovoid in shape. The seeds are light with a white pappus whose silky hairs are 5 – 8 mm long. They are wind- and water-borne.

Sow Thistles have been used as fodder, particularly for rabbits, hence other common names of ‘hare thistle’ or ‘hare lettuce’. They are also edible to humans as a leaf vegetable; old leaves and stalks can be bitter but young leaves have a flavour similar to lettuce. Going by the name puha or rareke (raraki) it is frequently eaten in New Zealand as a vegetable, particularly by the native Maori. When cooked, it tastes a little similar to chard.

The larvae of the Tomato Grub Helicoverpa armigera use this as a food plant.


Photographs taken on the Picnic Bay foreshore 2009
Page last updated 6th April 2019