FTEN THOUGHT of as a fruit, the first spring offering available to put into a pie, rhubarb (Rheum rhaponticum) is actually a vegetable and a member of the buckwheat family. This hardy perennial with an affinity for cool climates was known first in ancient Asia, where its roots were used medicinally as a purgative and astringent. The caravan trade that developed with Baghdad brought the plant to the Middle East and eventually to Europe. It was cultivated as a gardener's curiosity in England in the late 18th century and finally came into its culinary identity in the 19th century, when people realized that the rosy, succulent stalks were edible and nutritious. (The leaves, however, are bitter and poisonous.)

In The Cook's Oracle, published in London in 1823, rhubarb is referred to as "spring fruit" and appears in five recipes, including a mock gooseberry sauce and a soup in which four dozen rhubarb "sticks" are stewed with onion, carrot, and ham in consomme.

In this country many people think of rhubarb simply as pieplant. However, it is also a versatile ingredient in marmalade and chutney, cakes and quick breads, soup, and homemade wine. And to the food gardener, a patch of rhubarb is a must. Left undisturbed and given an annual feeding of compost and fertilizer, rhubarb will produce for 20 years or more, the crown jewel of the vegetable garden.