Milk thistle

A few days ago I had a call from a landowner who had unusual, unidentified thistles flowering on the edge of one of their fields. They turned out to be two milk thistles Silybum marianum, easily identifiable by the white variegated veins on their leaves. They are about five feet tall and are native to southern Europe, but have been introduced to many countries. They turn up sporadically in Britin, usually on waste ground, though rarely up here in County Durham. 

The plants are painfully prickly, along the leaf margins and especially on the tip of the bracts that surround the flowers. Milk thistles are biennials and it looks like this is now a small, self-sustaining population. Seeds might have arrived originally in animal feed.

I was first shown one here a couple of years ago, but then it was late in the season and all the flowers had run to seed (see bottom photo). This is the first time I've seen it in flower.