I was checking out at the grocery store the other day when the clerk asked whether I wanted the green tops removed from my carrots. I started to reflexively answer "yes," as I always have except for that brief period I was in charge of feeding my daughter's guinea pig Dovey.

But this time I hesitated. Dovey has long since left the building, but I had a sudden flash of what those carrot tops smelled like when I was chopping them up — intensely green, like turbocharged parsley.

I already had a big, old gnarly celery root, and I thought for a moment about how those two might go together. At first it was just a bit of whimsy: What if I combined one common vegetable's little-used top with another common vegetable's little-used bottom?

Then I pinched a bit of carrot green and tasted it. It was pretty much as I remembered, but with a touch of spice and even a hint of lemon that I'd never noticed before. I figured that since I already had one weird vegetable in my basket, I might as well go all the way. I told the clerk to leave the tops on.

When I got home, I prepared the celery root as I usually do — cutting away the tough, hairy peel, and then carefully slicing the crisp ivory flesh into sticks about the size of toothpicks. But rather than dressing these with a mustardy mayonnaise as I normally would, I whizzed together a vinaigrette made with olive oil, a hint of garlic, lemon juice and a handful of chopped carrot tops.

The result was lovely: The sauce was a vivid green that barely clung to the cream-colored celery root, with a few flecks of darker leaf for emphasis. And it tasted even better. The slight spiciness of the carrot tops perfectly complemented the bracing celery root. My brother-in-law from Oklahoma — who had never tasted celery root — was visiting that night and had thirds.

That started me thinking about how many other foods like that there might be — plants where one part is treasured but the rest is trash. How much good stuff is going straight to our rabbits?

Vegetables, by definition, are the parts of plants that don't contain seeds (those with seeds are fruits). That means, for the most part, the leaves, stems and roots — and in most plants, we eat only one of those three, discarding the rest.

We eat all kinds of roots without giving them a second thought: carrots, turnips and beets are just a few. But some are less familiar. In addition to celery root, there's also parsley root, which has a lovely root-vegetable sweetness spiked with a hard green core — it tastes to me like a cross between parsley and parsnip. Cook it as you would a carrot or a turnip; it is particularly good in soups.

Spinach roots are used as vegetables in the Middle East, while cilantro roots are used in spice pastes in Southeast Asia. In both cases, the root is similar in appearance and flavor to the stems — somewhat like a milder version of the leaf.

We eat lots of stems — celery, for example, and asparagus (which is the stem of a fern; left to grow, it develops lovely, frilly foliage). Then, of course, there are broccoli stalks, which are the stems. A small industry has sprung up around using what is left over when broccoli has been trimmed to its florets. The most common is shredding the stems into broccoli "slaw."

But I peel and cube the stalks and turn them into a pasta sauce. Add them to the pasta water after the dried noodles have been cooking for about five minutes, then drain everything at the same time and add it to a skillet of hot, garlic-scented olive oil. Dinner couldn't be simpler.

My friend Martha Rose Shulman makes a wonderful "drinks snack" of broccoli stems peeled and pickled with some chopped garlic.

Mild to pungent

And there are all manner of greens — some of them quite pungent, others more docile. Carrot tops belong in the first category, as do the tops of radishes, which have a distinctly peppery bite. Purée them with creamy, fresh goat cheese to make some nice crostini (be sure to wash the radish tops thoroughly — they harbor an unbelievable amount of sand).

I also use them to make a simple salad to garnish grilled meats. I just quarter the radishes lengthwise with the tops attached and dress it all with vegetable oil, red wine vinegar and a couple tablespoons of the carving juices.

You can toss these pungent greens in a salad — with discretion. (Remember, with vegetables as with people, too much personality can be every bit as bad as too little.) Or blanch, chop and combine them with milder ingredients such as rice or ricotta to make a risotto or a filling for ravioli.

Other, less rowdy greens are more adaptable. In fact, some may have sneaked right past you. Look carefully at most mesclun salad mixes and you'll find baby beet greens. And one of my favorite ravioli fillings is nothing more than beet greens that have been cooked briefly with garlic and then mixed with ricotta.

There is enough of the beet root's bright red betalain pigment in the leaves to tint the cheese a delicate pink. Serve this with the simplest sauce — melted butter flavored with fresh sage — and a generous dusting of Parmigiano-Reggiano.