Blueberries are a widely distributed and widespread group of perennial flowering plants with blue or purple berries. They are classified in the section Cyanococcus within the genus Vaccinium. Vaccinium also includes cranberries, bilberries, huckleberries and Madeira blueberries. Commercial blueberries—both wild and cultivated — are all native to North America. The highbush varieties were introduced into Europe during the 1930s. Blueberries are usually prostrate shrubs that can vary in size from 10 centimeters to 4 meters in height. Blueberries contain anthocyanins, other polyphenols and various phytochemicals under preliminary research for their potential biological effects.