Okay ...
Nebari
Also known as "buttressing", nebari is the visible spread of roots above the growing medium at the base of a bonsai. Nebari help a bonsai seem grounded and well-anchored and make it look mature, akin to a full-sized tree.
That makes sense to see what grows here. That link is helpful although I wish it was listed by zone instead of by plant/tree. We really want to try a mountain laurel and plan on wandering around today to see what might be an appropriate specimen. My plan is to take some pictures to bring with me of several different options and will focus the pictures on the bottom foot of the plant. We also have some beautiful maples -- I'm not sure what they are but most around here tend to be sugar maples - Acer Saccharum.