Adventurers and archaeologists have spent centuries searching for lost cities in the Americas. But over the past decade, they’ve started finding something else: lost farms.

Over 2,000 years ago in North America, indigenous people domesticated plants that are now part of our everyday diets, such as squashes and sunflowers. But they also bred crops that have since returned to the wild. These include erect knotweed (not to be confused with its invasive cousin, Asian knotweed), goosefoot, little barley, marsh elder, and maygrass. We haven’t simply lost a few plant strains: an entire cuisine with its own kinds of flavors and baked goods has simply disappeared.

By studying lost crops, archaeologists learn about everyday life in the ancient Woodland culture of the Americas, including how people ate plants that we call weeds today. But these plants also give us a window on social networks. Scientists can track the spread of cultivated seeds from one tiny settlement to the next in the vast region that would one day be known as the United States. This reveals which groups were connected culturally and how they formed alliances through food and farming.

Natalie Mueller is an archaeobotanist at Cornell University who has spent years hunting for erect knotweed across the southern US and up into Ohio and Illinois. She calls her quest the “Survey for Lost Crops,” and admits cheerfully that its members consist of her and “whoever I can drag along.” She’s published papers about her work in Nature, but also she spins yarns about her hot, bug-infested summer expeditions for lost farms on her blog. There, photographs of the rare wild plants are interspersed with humorous musings on contemporary local food delicacies like pickle pops.

Native to the Americas, erect knotweed grows in the moist flood zones near rivers. It’s a stalky plant with spoon-shaped leaves, and it produces achenes, or fruit with very hard shells to protect its rich, starchy seeds. Though rare today, the plant was common enough 2,000 years ago that indigenous Americans collected it from the shores of rivers and brought it with them to the uplands for cultivation. Archaeologists have found caches of knotweed seeds buried in caves, clearly stored for a later use that never came. And, in the remains of ancient fires, they’ve found burned erect knotweed fruits, popped like corn.

Mueller told Ars Technica that erect knotweed was likely domesticated on tiny farms on the western front of the Appalachians. There are clear differences between it and its feral cousins. After years of comparing the ancient seeds with wild types, Mueller has found two unmistakable signs of domestication: larger fruits and thinner fruit skins. We see a similar pattern in other domesticated plants like corn, whose wild version with tiny seeds is almost unrecognizable to people chomping on the juicy, large kernels of the domesticated plant.

Obviously, bigger seeds would make the erect knotweed a better food source, so farmers selected for that. And the thinner skin means the plants can germinate more quickly. Their wild cousins evolved to produce fruits tough enough to endure river floods and inhospitable conditions for over a year before sprouting. But farm life is cushy for plants, so these defenses weren’t necessary for their survival under human care.

Still, even the domesticated fruits of the erect knotweed have skins so tough that Mueller has not been able to crack them using the stone tools typical of the Woodland era. Working with a team at Cornell, she’s been trying to reverse engineer how they could have been eaten.

“The fruit coat is really hard, and it would have been necessary to break through it,” she mused. “It’s like buckwheat—the sprouts are nutritious. So maybe they ate the sprouted version.”

As for whether early Americans ate popped knotweed like popcorn, she was less certain. “The only way to preserve it is to burn it, so [the remains we find] could have been accidents while cooking. It might have been for drying.” But yes, people from long ago might have munched on popweed.

Another possibility is that the seeds were soaked in lime before being turned into a hominy-style porridge. Ancient Americans used lime—the chemical, not the fruit—to soften the hulls of maize before cooking it, in a technique called nixtamalization. It’s very likely the Woodland peoples used this prehistoric form of culinary science on other plants, too. So people 2,000 years ago may have been eating a rich, knotweed mush.

Mueller is currently cultivating her own erect knotweed to test various forms of preparation, but she’s not quite ready to go into the kitchen yet. “I’m trying to be a good farmer and put my seeds back first,” she said. “In five years of looking, I’ve only found seven populations of this plant. I want to conserve the seeds as much I can.” She’s going to accumulate a sizable cache of seeds before wasting them on dinner.

A history of civilization in food

Because ancient people in North America built mostly with perishable materials, traces of their farms are all we have left of their civilizations. With a few exceptions, they didn’t leave monumental pyramids behind or sprawling plazas. But their ability to domesticate plants is as much a testimony to their cultural sophistication as any stone temple.

In a recent paper for the Journal of Anthropological Archaeology, Mueller describes finding the earliest known example of domesticated erect knotweed at a site called Walker-Noe in central Kentucky. She found it mostly by accident. She had assumed, based on previous studies, that knotweed was domesticated in Illinois, possibly about 1,200 years ago. But then she spoke with a Kentucky museum curator who told her about a mysterious grave from the 2,000-year-old Hopewell culture, found stuffed with seeds.

Examining the seeds, Mueller identified them as domesticated erect knotweed. This find makes the plant’s domestication roughly a millennium older than previously thought. But given that these fruits probably came after generations of breeding by farmers, it hints at a much older date.

Mueller believes that the Hopewell shared their seeds throughout many communities where people tended farms along the skein of rivers that connect the American South with the Midwest. But it also seems likely that the erect knotweed was domesticated at least twice: once in the Kentucky region where she found her sample, and once about a thousand years later in Illinois when the great pyramid city of Cahokia stood at the center of the Mississippian culture.

Many of these early farmers appear to have counted crops among their greatest creations. Crops were valued trade goods and shared with allies in the same way jewelry, projectile points, and fine pottery were. And, of course, they were placed in graves alongside other precious funeral goods. Farming was a science and key to survival, but it was also an art. Food and feasting were central to indigenous cultures in the Americas, just as they were to civilizations in Europe and Asia. Serving guests a delightful meal with many kinds of grains, breads, and oils would have been a source of pride and pleasure.

Losing a crop

Perhaps the strangest part of this story is the fact that people simply stopped cultivating so many crops that were central to their diets. Imagine what would happen if we decided to abandon wheat to the wilderness. Suddenly, there would be no more baguettes and pastas—not to mention cakes. Sure, we could make delicious breads from corn and tasty noodles from rice or beans. But for many of us, it would feel like an incredible loss of a comforting staple. No doubt, that’s how the loss of knotweed felt to aboriginal Americans, too.

It’s likely that the Eastern Agricultural Complex (EAC)—a catch-all term for the lost crops of North America—faded away slowly. Though we can't be sure what triggered its decline, Mueller thinks it may have suffered its first blow from one of the most popular crops in the Americas: maize, which came north from Mexico about a millennium ago.

“Maize is an amazing crop,” Mueller said. “All over the world, when it arrives, people give up their old crops and start growing it. It’s productive and has lots of sugar so it gives you quick energy.” By the time Cahokia was at its height in the 1000s, maize was already edging out crops like erect knotweed.

But the death knell for erect knotweed probably came from Europe. Archaeologists find no more examples of domesticated erect knotweed after colonists began to settle the Americas in the 1400s, destroying local civilizations as they went. “There was so much displacement, disease, and warfare over the next couple hundred years that a lot of knowledge was lost,” Mueller explained.

Still, a lot can be learned from America’s lost crops, and it’s not just about finding the next quinoa for health-food nerds. Mueller has been working with Smithsonian Institute anthropologist Logan Kistler to sequence the genomes of lost domesticates. He’s fascinated by how many of these crops went through an entire cycle of domestication and re-wilding in the past few thousand years. Most plants that we eat, from wheat and barley to dates and beans, were domesticated more than 10,000 years ago and never went back. The EAC offers an unprecedented glimpse at what happens to plants when we turn them into food crops. And these domestication events are recent enough that we can get good genomic material from samples.

We have a fairly good sense of how domestication affects animal species over time. Domesticated pigs, horses, dogs, and even humans have all undergone physical changes, often described as “paedomorphosis,” which means retaining infantile body features (softer faces, smaller bodies) throughout life. But we’re just starting to understand plant domestication. “These crops have a good archaeological record that's well preserved,” Kistler said. “It gives us a chance to study domestication in real time, with a good record of what comes in between wild and domestic varieties.”

The EAC is also exciting for Kistler because it represents a diverse group of plants. Until recently, archaeo-botanists looked mostly at domestic plants emerging in the Fertile Crescent over 10,000 years ago during the Neolithic—but these are just grasses and legumes. In the Americas, Kistler explained, “We’ve got five good domesticated species. They’re taxonomically extremely diverse and yet grown in same fields and harvested at the same time. It builds in a little bit of control for looking at multiple species.”

Once he’s been able to sequence these crops, we may begin to see common domestication patterns across plant species. Likely they’ll be things like fast germination and larger fruit size, but we may find some surprises, too.

For Mueller, the search for erect knotweed isn’t just about understanding the mechanisms of domestication. It’s also about coming to terms with everything we’ve lost.

“I want to identify as many populations of these species as possible before they go extinct, because they are all threatened,” she said. She’s learned about how ancient Americans encountered these plants and how they incorporated them into their lives. But she’s also learned about how much the American landscape is still changing.

“I was out from October to November, driving around looking for populations of these plants. Partly it’s based on records from botanists going back at least 100 years.” Sometimes plants are still growing where they were a century ago, she said, but sometimes they aren’t.

“You realize how much the land has changed even in 100 years,” Mueller reflected. “There are so few places for native species to grow.”