Pecan trees, armored with scaly, gray bark and waving their green leaves in the breeze, grow in neat, uniform rows upon the Southern U.S. landscape and yield more than 300 million pounds of thumb-sized, plump, brown nuts every year. Native to the United States, they’ve become our most successful home-grown tree nut crop. Hazelnuts originated here too, but they come from a shrub, which can be trained into a tree. Almonds come from Asia. Peanuts, which aren’t actually nuts, hail …