I also discovered from that wretched catalogue that what I thought was a globe artichoke is probably a cardoon. The picture I took of one on an Italian allotment in the summer looks identical to the illustration of a cardoon in the Chase catalogue, where it says: "Cardoon is a close relative of the Globe Artichoke with spinier leaves and a non-edible lavender flower head to cut and dry. The stalks are tender and delicious when stripped and cooked." So. There you are. No artichokes next summer after all.