CUERNAVACA, Mexico — In the greenhouses of Mexico, people tell the story of the poinsettia plant with a touch of regret.

Back in the early 1800s, the first U.S. ambassador to Mexico, Joel Roberts Poinsett, took home a Mexican plant that turned a brilliant red in the winter. Mexicans called it nochebuena, or Christmas Eve plant. Americans named it after Poinsett.

Now, the United States produces more poinsettias than any other country, patenting new varieties and reaping about $260 million a year in sales. Mexico, on the other hand, can't sell the plants in the United States because of restrictions on importing Mexican soil.

"It's our plant, but now they have the patents and the name, too," said Diana Esquivel, financial manager of Finaflor Nurseries in Cuernavaca, 40 miles south of Mexico City.

The ban has been around for decades. It probably dates from the early 20th century when modern quarantine laws went into effect. Meanwhile, poinsettia sales have been growing steadily in the United States: They rose from 56 million plants in 1992 to 68 million last year.

Mexican growers believe they can compete north of the border and even have their government's backing.

For now, the only nochebuenas that Mexico can export are green cuttings the size of toothpicks, which U.S. growers cultivate and turn into finished plants. Many of the big American nursery suppliers have operations in Mexico to produce cuttings.

A cutting costs about 10 cents, a finished plant as much as $15 in the United States. A similar plant in Mexico sells for $2 to $5.

"Just imagine how well we could do if we could sell these plants in the United States," Esquivel said as she strode through rows of fiery Freedom Reds, glorious Red Angels and speckled Gingerbells. "The Americans don't have big plants like these here. They would love them."

Officials at the Mexican Embassy in Washington think so, too, and have been lobbying the U.S. Department of Agriculture to allow in plants with artificial soil, either the vermiculite nuggets found in some potting soil or a substitute made of ground-up coconut shells. Both would be sterilized before being used for exports, said Enrique Lobo, head of agricultural affairs at the embassy.

"These are high-tech substitutes, and I think eventually they'll be approved," he said.

Mexico has a similar ban in place on imports of U.S. soil, probably as a tit-for-tat measure, some growers said.

Jose Luis Vega, owner of Dream With Colors Nursery in Phoenix, said he empathizes with Mexican growers but that American nurseries deserve credit for turning poinsettias into an industry.

"Henry Ford came out with the first Ford, but other people contributed to making cars better after that," he said. "The U.S. people have put a lot of research into the nochebuenas, coming up with all kinds of new colors and shapes."

Especially frustrating to Mexican growers is that Canada is allowed to export potted poinsettias to the United States. In 1997, the two countries began a joint certification program for greenhouses, making it easier for plants to move across the U.S.-Canadian border.

"A lot of it has to do with the climate up there. It's colder, so we're not as concerned about parasites in the soil," said Melissa O'Dell, a spokeswoman for the USDA's Animal and Plant Health Inspection Service. "Also, we pretty much already have every (pest) they have up there in Canada."

In Mexico, poinsettia sellers line the roads near Cuernavaca and in the state of Mexico. Such nurseries have become high-tech affairs.

At Floraplant Nurseries in Tetecalita, 60 miles south of Mexico City, trucks roll through pools of disinfectant and workers must step on disinfectant-soaked pads before entering every greenhouse.

Potting soil is sterilized in a steam cauldron, water is irradiated to kill bacteria, and men in protective suits and respirators disinfect the greenhouses between crops.

In one greenhouse, horticulturist Carlos Martinez Barrera has selected the best 400 plants from 2004. Nearby, workers are using cuttings from those poinsettias to grow 130,000 "mother plants."

In February, workers will begin clipping young branches from the mother plants. They'll dip them in a chemical that causes them to grow roots, wrap them in moist paper and send them by plane to nurseries throughout the United States and Mexico.

Floraplant sells about 3 million cuttings each year, half of them to U.S. growers.

Other cuttings will go into pots in the company's own greenhouses, where growers carefully regulate the amount of light they get. When the amount of darkness per day reaches 12 hours and 20 minutes, the plants turn red.

Floraplant's export manager, Sajid Reyes Flores, said that the big Mexican nurseries are as sophisticated as American ones and that USDA concerns about Mexican potted plants are unfounded.

"We can handle the sanitary issues," Reyes Flores said. "This is really an economic issue; a lot of people would lose jobs in the United States."

"The Americans have taken this plant of ours and really made it a business," said Javier Lozana, a consultant who helps Mexican nurseries with exports.