Early settlers loved the pumpkin. But it was Mexico’s favorite first.

It’s been 400 years since the recently arrived Pilgrims and resident Wampanoags held a three-day diplomatic feast that historians later described as the first Thanksgiving. And it’s been 200 years since Sarah Josepha Hale, an early arbiter of good American taste, suggested in a novel that a turkey should fill the meal’s centerpiece, with pumpkin pie occupying “the most distinguished niche.” 

But how exactly did the humble pumpkin – a stringy squash generally overshadowed by its regular companions of sugar, cinnamon, nutmeg, ginger, and cloves – come to secure such a hallowed role in the most American of holidays? What does the pumpkin’s appearance on tables across the United States each November say about cross-cultural traditions?

The answers may lie not along the shores of Cape Cod, Massachusetts, but much farther south – in Mexico. “In our culture, nothing goes to waste from the pumpkin plant,” says Mely Martínez, author of the cookbook “The Mexican Home Kitchen,” from her home in Frisco, Texas. “I am from Tampico [on Mexico’s Gulf Coast], and there have been discoveries in caves there by archaeologists who found pumpkin seeds from 10,000 years ago.”

Pumpkin – and all its varieties – is indigenous to Central and South America. Mexican cooking, for example, incorporates both sweet and savory uses for the entire pumpkin plant, says Ms. Martínez. The tender leaves are used in soups, and the flesh is used as filling in everything from tamales to empanadas to tortillas. Even the pumpkin seeds are boiled or roasted, coated with sugar or salt and eaten as a snack, ground into a paste for green moles, or rolled out into a sweet nougat for candies. 

Mexican pumpkins, broadly known as calabaza de castilla, have a darker and thicker skin than the bright-orange sugar pumpkins popular in the U.S. Calabaza (Spanish for pumpkin) was discovered by Spanish conquerors, goes one theory, who took samples home to Queen Isabella of Castile in the late 1400s along with gold and other riches. She gave it the royal nod of approval, thus calabaza de castilla, says Ms. Martínez.

But the Spaniards were not the only ones intrigued by this round ambassador from the New World. When interacting with Indigenous peoples, the English also encountered pumpkins – they carried samples back to the motherland, and borrowed the French term for the squash when they started writing about “pompions” in cookery books in the 1600s.

“You don’t see pumpkin pies turn up [in cookbooks] until about the 1650s,” says Kathy Rudder, curator of craft and reproduction artifacts at Plimoth Patuxet Museums in Plymouth, Massachusetts. “In fact, even one of those recipes is actually taking the pumpkin and hollowing it out, filling it with a milky custard, baking it, and using the pumpkin [skin] as a crust.”

Settlers sang their gratitude for the fortitude of the squat produce when wheat was reluctant to grow in the stony fields of New England. Part of a stanza in the “Forefathers’ Song” of 1630 goes, “Instead of pottage and puddings and custards and pies, / Our pumpkins and parsnips are common supplies; / We have pumpkins at morning and pumpkins at noon, / If it was not for pumpkins we should be undone!”

The Plimoth Patuxet Museums (formerly Plimoth Plantation) is honoring the 400th anniversary of the first Thanksgiving with an exhibit – “We Gather Together: Thanksgiving, Gratitude, and the Making of an American Holiday” – that traces the diplomatic purposes of the meal through the centuries and includes a timeline of tables punctuated with place settings featuring notable dinners throughout history. 

“What we are showing on the tables is something called stewed pompion, which is first written down in 1672 by John Josselyn,” says Ms. Rudder, who keeps a binder full of historic pumpkin references. “He calls stewed pompion ‘the ancient New England standing dish,’ ... [meaning it’s] something that’s on the table all the time.”

The English, who put everything in pies, began experimenting with apples and pumpkins. In 1796 Amelia Simmons described the recognizable Thanksgiving pumpkin pie in what is largely considered to be the first American cookbook, “American Cookery.” But that doesn’t mean the pumpkin pie was a new invention. Recipes in cookbooks tend to follow the times, not lead them, says Ms. Rudder. 

“Her recipe is kind of what we think of when we think of pumpkin pie. One quart of pumpkin stewed and strained, three pints of cream, nine beaten eggs, sugar, mace, nutmeg, and ginger laid into a paste – and she refers back to the recipe for the dough you should use,” she says.

There appears to be some universal agreement through the centuries – and across geopolitical borders – that although the pumpkin is sturdy, it doesn’t deliver the same palatable sweetness of butternut squash or the nutty flavor of acorn squash. Enter its companions of sugar and spices. “We cook pumpkin with piloncillo [brown sugar] and a little bit of water, cinnamon, cloves, and anise seeds. This gives it a lot of flavor, and we cook it until it is tender. Some people like to eat it in the morning in a bowl of warm milk with thick syrup. It is delicious,” says Ms. Martínez, describing calabaza en tacha (see recipe), or candied pumpkin, a traditional dish for Día de Muertos, an autumn Mexican holiday that honors loved ones who have died.

Ms. Martínez says pumpkins in Mexico were once cooked in tachos, large copper cauldrons used to make piloncillo. The pumpkins were softened in the molasses residue in the pots, leading to the name calabaza en tacha.

Sound familiar? Remember, the New England colonists also hollowed out pumpkins and filled them with milk and honey. 

But how did the pumpkin get from Mexico to New England in the first place? It’s an agricultural mystery that invites the imagination. Perhaps the seeds spread in a slow creep, carried in the stomachs of migrating animals. Or perhaps they traveled in the pocket of an ancient wandering explorer curious about what lay beyond the next northern peak, sowing diplomacy and pumpkin recipes as she went.