Rhubarb, which looks like a pink celery stalk, is botanically a vegetable, but it is used as a fruit, largely in pies and sauces. The ancient Chinese cultivated the plant for its roots, which reputedly have medicinal properties. The roots and leaves aren't eaten; indeed, the leaves are highly poisonous. At one time, the toxicity was attributed to their exceedingly high levels of oxalic acid, a substance that can interfere with iron and calcium absorption. However, the exact source of the leaf toxin has yet to be determined, since rhubarb stalks also contain significant amounts of oxalic acid (as do a few other foods, such as spinach). Rhubarb stalks are extremely tart and they require sweetening to make them appetising. This can increase their calorie content considerably.

Buying
Choose well coloured, good sized, straight, firm crisp stalks. Avoid stalks that are limp. If the leaves are attached, they should look fresh and crisp; small leaves usually indicate younger, more tender stalks.

Storage
If you buy rhubarb stalks with the leaves still attached, cut off the leaves as soon as you get home. Never eat the leaves, raw or cooked: They are poisonous. Place the stalks in plastic bags and store them in the refrigerator crisper, where they will keep for about a week.