When we talk about early gardening in North America, most people think about the “three sisters” system of farming, in which indigenous people interplanted corn, beans and squash. But there were other systems of agriculture as well, including the cultivation of wild, non-domesticated plants. Researchers in British Columbia recently found the first evidence of a wild “wapato garden” tended by the ancestors of the Katzie First Nation.

In the Pacific Northwest, wapato tubers from Sagittaria latifolia, otherwise known as arrowroot, arrowleaf or arrowhead, were a staple crop. Growing on river banks and in wetlands, native communities dug them up, roasting them whole or drying them and pounding them into a meal for storage. Meriwether Lewis, during the Corps of Discoveries expeditions across the west, noted that the chestnut-like water potatoes were an important trading commodity and stopped to observe women collecting the tubers in 1806, writing:

“by getting into the water, Sometimes to their necks holding by a Small canoe and with their feet loosen the wappato or bulb of the root from the bottom from the Fibers, and it imedeately rises to the top of the water, they Collect & throw them into the Canoe, those deep roots are the largest and best roots.”

According to Geordon Omand of the Canadian Press, road building crews near Pitt Meadows, about 20 miles from Vancouver, came upon a 450-square-foot platform made of flat stones packed tightly into single and double layers. Archeologists called in to assess the site determined that it was a wetland wapato garden. In the past, the area was covered in shallow water and silt. The stone platform was constructed to prevent the tubers from rooting too deep, making it easier to pull them out of the muck.

Lizzie Wade at Science reports that researchers pulled up 4,000 wapato tubers from the platform, as well as pieces of 150 wooden digging tools, carved into shapes similar to a trowel. Those materials were dated to around 1,800 BC making the site roughly 3,800 years old and the oldest evidence of people cultivating wild foods in that area of North America.

“This is as important to us as the Egyptian pyramids, or the temples in Thailand, or Machu Picchu,” Debbie Miller, who works with the Katzie Development Limited Parternship, the tribally owned archeological firm that excavated the site, tells Omand.

Miller says that their excavations show that the gardening technique actually improved the health of the wetland ecosystem. Sedimentary analysis showed that soon after the site was abandoned, it acidified and dried up.

Despite its importance to the Katzie, the site was filled in after the excavation and covered by a public road. But tribal members—and anyone willing to dig in the muck—are able to get a taste of the ancestral staple. Edible species of Sagittaria exist in almost all wetlands in North America, and some tribes in the Pacific Northwest even host community harvests of the plant. In fact, in 2011, reports Courtney Flatt at OPM Radio, the Yakama Nation in Washington State was surprised when they restored some wheat fields into wetlands and wapato tubers that had lain dormant for decades sprang back to life, allowing tribal elders to munch on the traditional water potato for the first time in 70 years.