I thought this might be Hieracium, but the jagged leaf margins up the stem don't match a description I found, and I didn't remember to photograph the ones at the ground.
Thanks, Tyrlych. I don't see S. palustris as occurring around here. Maybe Sonchus arvensis? From E-flora BC, "Mesic to dry ditches, roadsides, disturbed areas and gardens in the lowland, steppe and montane zones; common in S BC; introduced from Europe." Listed as Exotic. Well, I needn't have felt stupid for forgetting to photograph basal leaves - it's not supposed to have them.
