MEXICO CITY — Even though it's illegal, bars of acitrón are stacked in nearly every stall at the Merced market in Mexico City.
They look like lemon bars. But they're pieces of barrel cactus that have been chopped up and then seeped in vats of sugar until they're crystalized.
Edith Hernández Torres, who runs a shop here, wraps hers in cellophane. She says acitrón is special, that it tastes nothing like the candied lemon or sweet potato or the pineapple she also sells.
"It has a chewy texture," she says, "like something roasted."
The Mexican government began banning the sale of acitrón in the early 2000s. That's when they found that the biznaga cactus — a species of barrel cactus — was in danger of extinction due to overexploitation.
Hernández knows acitrón is illegal, but her customers demand it. When NPR asks if she doesn't feel bad about selling something that's going extinct, she shrugs.
"Our whole planet is going extinct," she said.
As she speaks, María Julia Gutiette picks up a bar of acitrón. She does it gently, like she's picking up a bar of gold.
Her husband and this nation were born on the same day: Sept. 16. So, every year, Gutiette buys the pears, the peaches, the pink pine nuts and the acitrón to make the make chiles en nogada, a traditional dish that is eaten from August to early October.
"Traditions are the salt and pepper of life," she said. "They are that extra something that makes life extraordinary."
When she says this, her eyes tear up. She never had chiles en nogada growing up because the ingredients were too expensive. But then, she studied, she became a nurse and moved to Mexico City.
"When you grow up and make your own money, you save for nice things," she said. And so for Independence Day, she wants to treat her family to something special. And the chiles en nogada, she says, must be made with acitrón.
"Cacti don't grow like grass"
At the National Autonomous University of Mexico's botanical garden, there's a whole section dedicated to barrel cactuses. It's the kind of cactus that played an important role in Mexico even before the Spanish introduced the sugar that made it so sweet. The cactus appears in the Aztec codices and the name comes from a Nahuatl word that means a pot covered in spines.
"In Mexico, we have more than 150 species of biznaga," said Salvador Arias, a biologist who runs the botanical gardens. Most of them are going extinct in the wild.
He points toward the golden barrel cactus whose spines make it look like a rising sun. Mexico built a hydroelectric dam, where these golden barrel cactuses live and in an instant their environment was destroyed and this species was almost wiped out.
Some of the cacti are 40 years old and they reach to your thigh. Others are 8 years old and they are tiny, just the size of your fist.
"These cacti don't grow like grass, because their metabolism is especially slow," Arias said. "It's so slow they might grow millimeters a year."
This means farming the biznaga is neither practical nor profitable, so they're harvested from the wild. That has left dozens of species on the verge of extinction.
"But I'm an optimist," he said. "I believe that cacti have evolved in the past to thrive in contrasting environments. I think they can do it again."
He walks toward his collection of nopales, the cactus that adorns the Mexican flag, the cactus that is an everyday staple in Mexican kitchens. But this species is thriving because of an evolutionary adaptation.
"The nopal is modular," he said. It grows in a kind of chain, so unlike the biznaga, humans can cut off and eat the newest shoots without killing the whole plant.
"The Soul of Mexico"
The chef of the restaurant Azul does not use acitrón. But his chiles en nogada are legendary.
They're so important that when they begin serving them in August, the table cloths go black and the silverware goes gold.
"It's a yearly ritual," chef Ricardo Muñoz Zurita said.
First, the waiters bring out a tray of poblano peppers topped with a green, white and red bow. And after they place one on the plate, they douse it with a creamy walnut sauce, as silky as melted white chocolate.
"This plate is the soul of Mexico," said Muñoz. "It tastes like the motherland, like independence. It tastes like Mexico itself."
Muñoz makes a recipe from 1821, which is what was served to the independence hero Agustín de Iturbide in Puebla right after signing a treaty that consummated Mexico's independence.
But a few years ago, the chef stepped away from that recipe and stopped using biznaga. Instead, he started using candied chilacayote, which is a type of squash.
"In truth, it doesn't affect the final taste," he said. Indeed, he conducted blind taste tests and no one could tell the difference.
"But Mexicans hold tight to traditions," he said. "If you learned to make it from your grandma or mom and they used acitrón, I understand why they would want to keep using it."
But he feels a responsibility not to use it, because he wants barrel cactuses to survive in the wild.
"We humans have the great power of adaptation," he said.
To save the barrel cactus, he said, we'd be wise to use it.
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