Annual, spreading by seed which have short plumes (pappus) of silvery-green hairs. The young basal leaves are not spiney and are a different shape to the later mature ones which arise alternately on the upright hollow stem, and can be added to salads.
Flowers from June to August, bright yellow.
Height - up to 90 cm.
Weedkillers to use:-
Dichlobenil prevents emergence of seedlings amongst established woody plants, for up to one year.
Paraquat, Diquat kills on contact.
Glyphosate, systemic action killing the whole plant.

Also Smooth Sow-thistle ( S. oleraceus) an annual with similar young leaves, and the Perennial Sow-thistle ( S. arvensis ) with creeping roots and seeds. Both have similar bright yellow flowers.

Follow these links for further details on Weeds, Weed Removal and Weed Prevention.