The line between whether a plant is a "tree" or a "shrub" is sometimes very thin and quite blurry! We use the following criteria to decide which type applies to a certain plant:
Abelia x 'Canyon Creek'
Aesculus flava, Yellow Buckeye
Aesculus x splendens
Asimina triloba, Paw Paw
Buxus microphylla var japonica 'Borderline'
Callicarpa americana 'Welch's Pink'
Calycanthus x raulstonii 'Hartlage Wine'
Caryopteris divaricata 'Snow Fairy'
Chamaecyparis obtusa 'Elmwood'
Chamaecyparis obtusa 'Golden Whorl'