Can you suggest a species name for an extremely tall thistle-like plant with very broad, grey-green leaves?

Question:This plant grows around six feet tall, and is definitely not invasive, although it does self-seed somewhat. It is rather like cardoon, but taller, with fewer leaves. A full-grown specimen makes a visual impact like a tall cactus. I have seen it in a few gardens, but never in a garden centre.

Answers:
stinging nettles