Many wildflowers and grasses that grow in Minnesota are common in other parts of North America, too. Sites with photos and information that I have found helpful are:
Dictionary of Common Names of Great Plains Plants: What one site calls Field Sagewort, another calls Tall Wormwood. This site can help clear the confusion on common names if you have a plant's scientific name.
USDA Plant Database: I often use the distribution maps to help identify native plants in my area.