Prickly sow thistle: Sonchus asper
Field Sow-thistle, Marsh Sow-thistle, Wet Ground Sow-thistle: Sonchus arvensis ssp. uliginosus (Synonyms: Sonchus arvensis var. glabrescens, Sonchus uliginosus) -
Prickly Sow-thistle, Prickly Sow Thistle, Spiny Leaf Swo-Thistle: Sonchus asper (Synonym: Sonchus asper ssp. asper) - An erect fleshy annual from 60-100 cm high. The leaf margins have prickly teeth and the basal lobs of the leaves are rounded where they clasp the stems.
Common Sow-thistle, Common Sow Thistle: Sonchus oleraceus - An erect fleshy annual from 50-100 cm tall. The leaf margins are soft-toothed and the basal lobes of the leaf are acutely angular rather than rounded. The basal leaves are stalked while the upper stem leaves are clasping. Most of the leaves are deeply 1-3 lobed. The numerous flower heads bear yellowish ray flowers.