Dear Key Lime,

Weather is beautiful. Wish you were still here, the pies just aren't the same without you.

IN THE FLORIDA Keys, where eating key lime pie is as important to a vacation as watching sunsets and snorkeling, there's a well-kept secret. Shhh, don't tell the tourists, but there are fruits traveling with false identities.

"Homemade Key Lime Pie" signs decorate U.S. 1 like Dart Drug marquees on Route 50. But key limes -- those small tropical fruits the color of lemons, the size of golf balls and a touch more tart than persian limes (the familiar green ones)--are practically extinct in Florida. Nowhere in the Keys are they grown commercially; locals' backyards are their only breeding ground.

Yet asking a restaurant if it uses real key limes in its pies is practically an insult. "Of course," is a frequent answer. But ask a restaurant to show you what a key lime looks like and it may be caught by surprise. Only twice out of several requests was one to be found.

On one occasion, a large persian lime posing as a key lime was brought to the table. It looked like a persian lime, tasted like a persian lime, but no, "This is a key lime," pronounced the waiter.

At another restaurant, the waitress boasted about the key lime pies made daily on the premises, from real key limes, naturally. None of the limes were to be found in the kitchen.

At the Green Tree Cannery in Islamorada, where they process key lime pie filling into flourescent green containers, cans lined the counter. "Do you use real key limes?" provoked the response, "What do you think?" The can lists, among other ingredients, "lime pure'e, modified food starch and sodium citrate."

In 1977, the state looked into the key lime question. Although there is a Florida statute that prevents restaurateurs from falsifying the identity of a food, according to Bob Donovan, assistant director of the state's Division of Hotels and Restaurants, it was concluded that calling pies made from any old limes "key lime pie," was not a violation of this law, as the recipes researched simply called for "lime juice." Donovan said his office does receive calls from disgruntled tourists, but that any key lime legislation would be difficult to enforce.

There's good reason key limes are hard to find in pies; they're hard to find whole. Of the two fruit markets in Key West, one sold the endangered species. But these were extras from the owners' tree; the other fruit market wasn't so lucky--and it wouldn't pay a seller $15 for a handful of the limes to resell.

In major supermarkets, produce workers said they periodically sell key limes when in season. But according to more than one extension service specialist, many of these are shipped from Mexico.

Key limes didn't always have it so rough. Brought over by West Indians, the original settlers of the Keys, key limes grew in groves until the 1920s and '30s, when the rest of the country was sipping cherry phosphates at soda fountains and southern Floridians were ordering key lime ades.

Yet they were gradually abandoned. Some peg a tropical storm to their death, but as Charles Walker, manager of the Florida Lime and Avocado Administrative Committees, said, "There's always been storms. You can always replant them." They didn't.

It was the persian or tahitian variety that stole the limelight. Economics was the impetus. According to Seymour Goldweber, an agricultural extension agent who has followed the condition of the key lime for the 55 years he's lived in southern Florida and insists that persian limes be called tahitian limes ("There's nothing tropical about the land that used to be Persia"), the key lime wasn't good enough. The reasons, according to Goldweber, are numerous:

Key limes have a short shelf life because they must be fully ripened when picked, so they don't ship well. Key limes have seeds, persian limes do not. ("Consumers would prefer to see all fruit with zippers on the sides.") Key limes are more labor-intensive to produce. It takes 600 to 800 key limes to fill a bushel box, 250 to 300 for persian limes. Key limes are seasonal and can only be grown in the tropics; persian limes bear fruit all year and can withstand colder weather conditions. Key lime trees can contract a serious disease problem when wet; the persian lime has more resistance. The "other lime" clearly has commercial advantages.

It's probably too late for the key lime--urbanization has set in, and the groves have been replaced with signs like "Key Lime Pie and N.Y. Cheesecake." It's the key lime, though, that still gets credit for its part in the pie. Goldweber said the name stuck because of tradition and history. And then there's the regional attraction. "People feel they have to have it the pie ," said Marilyn Broach of the Florida Lime and Avocado Administrative Committees. "It's like going to Boston and thinking you have to have scrod, like going to Seattle and thinking you have to have salmon."

So next time you go to the Keys, tell the locals all our chicken is fried in Maryland, all our bean soup made in the Senate ...