Pecan trees are a variety of hickory. They along with walnuts are among the nuts with the highest oil and unsaturated fatty acid contents. High oil content generally means fragile texture or easily bruised which increases the rate of staling or oxidation. Roasting will increase the rate too so best to store and freeze raw pecans. Store raw or roasted pecans in the freezer to protect them from becoming rancid. Carefully handled they can be stored for years in your freezer.
Wild pecans were enjoyed by native Americans who made it into a kind of milk for cooking and drinking. The earliest intentional planting may have been by the Spanish around 1700 in Mexico. The first improved varieties were made possible by a Louisiana slave named Antoine, who worked out how to graft wood from superior trees onto seedling stocks. Georgia, Texas and New Mexico are now the largest producers of pecans and the world's largest pecan nursery is in Lumberton, Mississippi.