Lettuce (Lactuca sativa) is an annual plant, whose leaves are harvested for culinary purposes. It probably originated from the Mediterranean, and the Romans used it as a soporific.
To grow, Lettuce enjoys rich, moist soil. It enjoys it so much so, that short of flooding it seems impossible to overwater lettuce. Hot weather and underwatering often cause lettuce to go to seed, at which point the leaves become bitter. Lettuce is also one of the few vegetables that can be sown successively in the same position.