[wikipedia] Acorn Information, Misidentifications, Hybridity: Quercus macrocarpa, the bur oak or burr oak, is a species of oak tree native to eastern North America. It is in the white oak section, Quercus sect. Quercus, and is also called mossycup oak, mossycup white oak, blue oak, or scrub oak. The acorns are the largest of any North American oak and are important food for wildlife. Bur oak is sometimes confused with other members of the white oak section, such as Quercus bicolor (swamp white oak),[6] Quercus lyrata (overcup oak), and Quercus alba (white oak). It hybridises with several other species of oaks. (link added by Mary Ann Machi)