I have many examples of small trees in pots which have remained small trees in pots even after 15-20 years.
- Korean hornbeam - in a pot since purchase in 2008: https://www.flickr.com/photos/norbury/albums/72157625467678128/
- Mountain maples/Rowan - since 2008 in a pot...
I have 50 species of trees, but nothing particularly unusual AND native to my zone. I have a couple of uncommon species which are not native here but which are greatly underrated:
- Chinese Ash
- Italian Alder