It's obviously a type of sunflower, not a type of artichoke (the latter designation coming from early explorers' comments re the taste of the tuber). And the "Jerusalem" component of the name is a corruption explained at World Wide Words:
...the Italians, who imported it first, called it girasole: “heliotrope”, or turning always to the sun. (In a slightly different form the same word turns up in English as a name for an opal that glows reddish in the light, the “fire-opal”.) Anyway, the pattern-matchers got hold of this plant name and turned it to “Jerusalem” in a twinkling.
