The Jerusalem artichoke has absolutely nothing to do with Jerusalem, and little to do with true artichokes. The first part of its name is due to the process of folk etymology. When it was first discovered, it was called Girasole, which is the Italian word for sunflower (it refers to the way in which the flowers turn towards the sun). The Jerusalem artichoke is a type of the sunflower, in the same genus as the garden sunflower Helianthus annuus. Later people thought that Girasole sounded like Jerusalem, so they called it that. In recent years, many people have taken to calling it sunchoke or sunroot to avoid this confusion.
The second part of its common name comes from its taste. The tuber, which is the only part used, tastes like a cross between radish and artichoke.
The tubers are gnarly and uneven, vaguely resembling ginger root, with a crisp texture when raw. Unlike most tubers, but in common with other members of the Asteraceae (including the artichoke), the tubers store the carbohydrate inulin (not to be confused with insulin) instead of starch. For that reason, they are an important source of fructose for industry. It also gives them a tendency to break down and dissolve when cooked, in addition to giving them a legendary facility to produce flatulence.
These vegetables are sold in the produce departments of supermarkets. The freshest roots are plumpish and vibrant in appearance. If left too long in the open, they become wrinkled and soft and can develop a bitter taste.