PHYTOLITHS FROM FOOD RESIDUES PROVIDE THE OLDEST DATE FOR USE OF WILD RICE IN MINNESOTA

Wild rice (Zizania palustris) has been harvested by the Ojibwe people of northern Minnesota for many years. Previously reported archaeological evidence for wild rice use dates back about 2,000 years ago. This study, based on radiocarbon dating of food residues in Brainerdware pottery from the Ogema-Geshik archeological site in Cass County, Minnesota, pushes the age of wild rice usage beyond 3000 years ago. The Ojibwe people are known to have harvested wild rice at this location for many years. In the past, when it was common for Ojibwe to use unglazed clay pots for preparing food, food was often left behind in the pot on purpose to help waterproof the interior of the pot. This food residue left behind contains phytoliths, microscopic opaline silica particles that can often be identified to the type of plant in which they were produced. Wild rice and corn are foods common to the Ojbwe, and wild rice is a sacred food source. It can be expected that pottery from Ojibwe land will contain food residues from both types of plants. Both wild rice and corn produce a rondel-shaped phytolith in the chaff of the plant. The chaff is a small percentage of food that is cooked; however, it produces abundant silica bodies, which form a large percentage of what remains in the food residues. Wild rice and corn rondels can be distinguished by their patterns of projections and indentations. Assemblages of phytoliths from corn and wild rice can be statistically identified by measurement of distances between these landmark features. Principal components analysis shows that the assemblage of phytoliths from the Brainerdware pot represents wild rice. Although our study demonstrates that wild rice was used in this area over 3000 years ago, it does not help to determine whether wild rice was growing there or was brought from another location.