I saw someone mention this plant on social media, looked it up and thought why haven’t I seen that, and the very next day there it was, growing amongst a riot of wildflowers and grasses alongside a smelly brook in a Cardiff park. This is Prickly lettuce (Lactuca serriola).

It’s described on the Naturespot website as:

Tall, greyish, stiff and erect plant to 1.8 metres. Stem sometimes bristly. Leaves alternate, oblong, prickly on margins and along the mid-rib beneath, sometimes irregularly lobed, clasping the stem with arrow shaped points. … Flowerheads pale yellow 11 to 13 mm numerous, in a narrow pyramidal panicle.

I wasn’t one hundred percent sure of my identification until I turned over a leaf to follow the leafhopper that had disappeared beneath and spotted that vicious-looking row of spines along the mid-rib (though they weren’t actually as vicious as they looked).