Milk thistle
Silybum marianum
Family · Asteraceae · Irritating

The big thistle with leaves marbled in white, as if milk had been spilled over them. Legend says it was the Virgin's milk, and the name stuck across half of Europe.
Roadsides and waste ground · Fields and pasture · Montado · Town and roadside
Also known asblessed milkthistle, Marian thistle
How to tell it
The white veins on green leaves are unmistakable and no other common thistle has them. A large purple head surrounded by strongly spined bracts.
What it is confused with
Purple milk thistle
Galactites tomentosa
It also has pale veins, but is much smaller with a pale lilac flower. Neither is dangerous; the difference is size.
What it is for
Peeled leaf stalks were eaten boiled in country cooking, like garden cardoons. The seeds are today a subject of pharmacological study, which is context and not an indication: none of it is prepared at home.
Traditionally used as food. This is not permission to eat it.
With documented traditional uses. Not a therapeutic indication and not a dose.