Pecans are actually not legumes as there are many distinct differences between the two. One of the primary differences between pecans and legumes is that legumes are vegetables which come from plants in the Fabaceae family.
Pecans, which are also referred to as Carya illinoinensis, is actually a species of hickory and comes from Mexico and North America. Another one of the distinct differences between nuts and legumes is that nuts typically have just one seed whereas legumes have more than one. It is highly uncommon for pea pods to have more than half a dozen peas in them.