The Jerusalem artichoke has no relation to Jerusalem, and little to do with artichokes. The name Jerusalem is due to folk etymology; when the Jerusalem artichoke was first discovered by Europeans it was called Girasole, the Italian word for sunflower. The Jerusalem artichoke is a type of sunflower, in the same genus as the garden sunflower Helianthus annuus. Over time the name Girasole transformed into Jerusalem, and to avoid confusion people have recently started to refer to it as sunchoke or sunroot, which is closer to the original Native American name for the plant. I used to grow these until they took over my vegetable plot. We enjoyed the tuberous roots sliced and baked. Very tasty - but flatulence making! They grow wild around here in Western North Carolina. Here's some great information about this pretty, edible (the tubers) plant: http://www.samcooks.com/food/vegetables/JerusalemArtichokes.htm
Update: 10/20 - this may be helianthus decapetalus.