A team of archaeologists and anthropologists, led by the University of Utah, has discovered potato starch residues in the crevices of a 10,900-year-old stone tool in Escalante, southern Utah — the earliest evidence of wild potato use in North America. This is the first archaeological study to identify a spud-bearing species native to the southwestern U.S., the wild potato (Solanum jamesii), as an important part of ancient human diets.
Dr. Louderback stands behind large stone metates, the grindstones on which ancient Native Americans processed their food. Image credit: University of Utah.
The potatoes we buy at the grocery store are all varieties of a single species, the potato (Solanum tuberosum), that was domesticated in South America, in the Andean highlands, between Peru and Bolivia, more than 10,000 years ago.
Since then, Solanum tuberosum has diversified into the reds, russets and thousands of other potato types for sale in markets around the world.
The new study deals with Solanum jamesii, a species found in the shady shelter of oaks, sagebrush and piñon pines across the Four Corners region of the southwestern U.S.
Also known as the Four Corners potato, the species is most abundant in the highlands of New Mexico, where its green leaves and delicate white flowers are scattered throughout piñon-juniper woodlands.
“Several Native American tribes, including Apache, Hopi, Kawaik, Navajo, Southern Paiute, Tewa, Zia and Zuni, consumed Solanum jamesii,” the scientists said.
“The groups used various cooking and processing techniques, including boiling the potatoes, grinding them into flour or yeast, and mixing the potatoes with clay to reduce bitterness. Some groups still tend their potato populations in cultivated gardens.”
“The long history could mean that the species was transported, cultivated or even domesticated. If true, Solanum jamesii would be the first example of a plant domesticated in the western U.S.”
“This potato could be just as important as those we eat today not only in terms of a food plant from the past, but as a potential food source for the future,” added senior author Dr. Lisbeth Louderback, from the University of Utah.
Dr. Louderback and her colleague, Bruce Pavlik, director of conservation at Red Butte Garden, analyzed stone tools from North Creek Shelter in the Escalante Valley, one of Utah’s oldest archaeological sites with an 11,000-year history.
Its residents were mostly hunters and gatherers until the Fremont and Ancestral Puebloan cultures arrived and began cultivating crops.
Today, the Southern Paiute inhabit this region along with descendants of Mormon settlers.
The researchers examined large sandstone slabs called metates and handheld grinding stones called manos, the ancient food processors on which people prepared meals.
They found microscopic starch granules that previous archaeologists never suspected were present.
“Grinding plant tissues with manos and metates releases granules that get lodged in the tiny cracks of stone, preserving them for thousands of years,” Dr. Louderback said.
“Archaeologists can retrieve them using chemicals, modern microscopy and advanced imaging techniques.”
All starch granules have concentric circles that grow outward like tree rings. The origin of growth begins with what’s called the hilum.
The majority of plant species have starch granules with hila at the center of the grain. However, the hila of granules filling the team’s microscope slides were off-center.
Only a few species from the Four Corners region produce starch granules with that specific characteristic; Solanum jamesii is one of them.
The scientists analyzed granules from modern-day Solanum jamesii to establish a set of five characteristics that accurately identified the wild potato, starting with the off-center hilum. Starch granules with five out of five characteristics were a verified wild potato.
They analyzed tubers from three different modern populations, 100 granules per tuber.
They checked for the characteristics on granules found on the ancient stone tools from North Creek Shelter.
Out of the 323 total starch granules, 122 had the off-center hilum. Of those, nine were verified Solanum jamesii and another 61 were either likely or possibly Solanum jamesii.
The findings appear today in the Proceedings of the National Academy of Sciences.
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Lisbeth A. Louderback & Bruce M. Pavlik. Starch granule evidence for the earliest potato use in North America. PNAS, published online July 3, 2017; doi: 10.1073/pnas.1705540114
