Thanks to Popeye, everybody knows that spinach is a nutritional powerhouse. Of all the cooked leafy greens, it's probably the most widely eaten. Nonetheless, it remains the butt of jokes, and many people shun it unless it's disguised in quiche or swimming in rich cheese sauce.

Other, less-known greens that also make the nutritional honor roll and which may please more palates often are ignored altogether. Even if you abhor spinach, you might become a fan of kale prepared with minced onion and vinegar, or fresh, steamed beet greens or collards. The point is to give them a chance in the first place.By getting more greenery into your diet, you'll be following one of mankind's finest and oldest traditions. Our earliest ancestors feasted on edible greens growing within easy reach above the ground. Young willow and birch shoots, tiny nettles, ferns and water weeds helped furnish the vitamins and minerals that man needed to evolve and thrive.

Later, the leaves of the artichoke plant - not the vegetable itself - were considered a delicacy in Roman times. In the long winters of the Dark Ages, the "silent centuries," poor peasants subsisted on bread and stewed cabbage, kale or onions washed down by primitive ale.

Spring greens have held a special place in history. Watercress and parsley are prominent at the Passover table. The observance of Lent is marked by green dishes such as lasagna verde. Wales even boasts a green vegetable - the leek - as its national plant.

Nutritionally speaking, few foods rate higher than greens. To start, they're one of the top sources of vitamin A. The thin leaves and stalks of greens contain large amounts of the pigment carotene, which the body converts to vitamin A. Just half a cup of kale, spinach, turnip or collard greens provides more than one and a half times the Recommended Dietary Allowance. And a single stalk of broccoli will give you all the vitamin A you need for the day.

Color is a key to nutrient richness. The darker the green or yellow of a vegetable, the more carotene it contains. The pale inner leaves of cabbage or lettuce have significantly less than the darker outer leaves.

Greens are also a fine source of vitamin C. That same large stalk of broccoli will give you one and a half times the RDA. Brussels sprouts, mustard and collard greens make similar contributions; kale and turnip greens provide even more. Both cabbage and spinach contain some vitamin C, too.

And let's not forget the B vitamins. A half cup cooked spinach or cabbage will supply, on average, 12 percent of the RDA for riboflavin, as well as helping to meet our requirement for both vitamin B-6 and folic acid, which is essential for the maturation of red blood cells. Folic acid actually derived its name from the Latin word for leaf, because it was first isolated from green leaves.

As for minerals, again you'll strike it rich with leafy vegetables. Spinach, beet greens, chard, mustard and turnip greens are all strong in iron. Broccoli and Brussels sprouts are decent sources, too. A half cup of cooked leafy vegetables also provides about the same amount of calcium as a glass of milk, as well as phosphorous and magnesium, with some trace minerals thrown in.

Greens even contribute vegetable protein of respectable quality. A cup of cooked spinach or dandelion greens contains 5 grams. While not of the same caliber, that's almost what you'd get from an ounce of meat. And if it's eaten along with protein from other types of foods, the body can use it as effectively as protein from animal food.

Considering this gold mine of nutrients, why do so many of us hurry through the produce section of the market, paying short shrift to the green array? Perhaps it's because some have never tasted greens properly prepared - for instance, steamed in very little liquid, cooked until still crisp and fresh-tasting. Vegetables certainly don't have to be boring. They can be served on their own or as part of a main dish. Spinach souffle, leek pie, lasagna verde and spring soup made with mixed greens brighten any menu.

Also delicious are steamed broccoli rabi (tender young leaves with tiny broccoli florets) served with lemon sauce, or steamed chicory with oil and garlic dressing as a bed for broiled tomatoes dressed with chopped green scallions. Leafy greens are also marvelous served raw and crunchy, as creative salad combinations.

So whether or not you like spinach, give other greens a try. You'll be pleasantly surprised, and we know you'll be doing yourself a nutritional favor.