From apples to zinnias, America's plants are largely imported. Most cultivated flowers, vegetables, fruits, grains, and grasses are not native, and 70 percent of our weeds have foreign roots. Coffee comes from Ethiopia, oranges and olives from Spain, watercress from England, clover from the Mediterranean; even the dandelion and daisy are transplants and mullein, that ubiquitous roadside border, also comes from Old World stock. Haughton has dug up not just country of origin for our green immigrants but also entertaining background and trivia. For example, William Penn once paid the equivalent of $4.65 for a pound of precious coffee and Shropshire doctor William Withering rediscovered that foxglove's digitalis had medicinal properties. Much of this, presented alphabetically, is gardenvariety history, and occasionally the tone seems appropriated from a rosy-cheeked juvenile. (Of Withering, hearing about a woman working with foxglove: ""He must drive out there this very day and see what the story really was."") But for the most part, it's got page-turning readability; even those disarmed to learn that crab grass is imported can enjoy the harvest.