What is the name of the broad expanse of flat land in the western United States and western Canada  where the species of plant called the Polygonum sawatchense of the buckwheat family be found?
Polygonum sawatchense Polygonum sawatchense is a North American species of plants in the buckwheat family. It in the western United States and western Canada, from the Pacific Coast to the western Great Plains, so from British Columbia south to California and east as far as New Mexico, Colorado, Saskatchewan, and the Dakotas.
Eriogonum heracleoides Eriogonum heracleoides (common names parsnipflower buckwheat, whorled buckwheat, and Wyeth buckwheat) has many flowering clusters that are cream or off-white in color. Its usual habitat is rocky areas such as sagebrush deserts and Ponderosa pine forests. Parsnipflower buckwheat is in the genus "Eriogonum" and the family Polygonaceae which is a family of plants known as the "knotweed family". It inhabits much of the western part of the United States.