Field Guide to Noxious and Other Selected Weeds of British Columbia
Perennial Sow-thistle (Sonchus arvensis) and Annual Sowthistle (Sonchus
oleraceus)
Photo courtesy Dean Swan, Washington State University (retired)
Provincial Noxious Weeds
Perennial sow-thistle is a creeping rooted perennial growing 0.4
to 1.5 metres tall; stems branch near the top; leaves with weak
marginal prickles clasp the stem; plants contain a bitter milky
juice; upper stalks and flower bracts usually covered in
gland-tipped hairs; yellow flowers up to 3.8 cm broad
often confused with annual sow-thistle (Sonchus oleraceus)
(Provincial Noxious) which is taprooted and has
much smaller flowers (less than 2.5 cm across) or spiny annual sow
thistle (Sonchus asper) which has sharp, spiny leaves and
smaller flowers.
Perennial sow-thistle with milky latex and clasping stem
Photo courtesy Dean Swan, Washington State University (retired)
Spiny annual sow-thistle
Annual sow-thistle
Photo courtesy Dean Swan, Washington State University (retired)
Photo courtesy Dean Swan, Washington State University (retired)
