Spring visitors to Great Smoky Mountains or the Blue Ridge Parkway will see ridges and valleys covered in flowering mountain laurels, rhododendrons, tulip poplars, dogwoods, black locusts and silverbell trees. A new study of nearly all the trees and shrubs in the southern Appalachians suggests that roughly half of the species can trace their relatives to thousands of miles away in Asia. Most of the rest likely arose within North America, the researchers say....