Originating in the Middle East, spinach was being grown in Spain during the 8th century, and the Spaniards are the ones who eventually brought it to the United States. Popeye's addiction to this "power-packed" vegetable comes from the fact that it's a rich source of iron as well as of vitamins A and C. But because spinach contains oxalic acid — which inhibits the body's absorption of calcium and iron — the truth is that its nutritional value is somewhat diminished. It's this same oxalic acid that gives spinach its slightly bitter taste, which is prized by some while others find it off-putting. Spinach has dark green leaves that, depending on the variety, may be either curled or smooth. The smaller New Zealand spinach has flat, spade-shape leaves that are often covered with a fine fuzz. Fresh spinach is available year-round. Choose leaves that are crisp and dark green with a nice fresh fragrance. Avoid those that are limp, damaged or which have yellow spots. Refrigerate in a plastic bag for up to 3 days. Spinach, which is usually very gritty, must be thoroughly rinsed. Frozen and canned spinach is also available. Spinach may be used raw in salads, or cooked (usually by boiling or sautéing) and used as a vegetable or as part of a dish. Many dishes that use spinach as an integral ingredient are appended with the phrase À la florentine.