I will explain the forms of canopies in the next blog, this one is concerned with which you can purchase trees.
1) Standard Trees, these have a clear stem of around 1.8-2.2 metres with a canopy above. From this a half standard (1 metre clear stem) and three quarter stem (rarer but 1.75m) are derived.
2) Feathered Trees, these have branches from near the base, so that there is no area of clear stem.
3) Multi-stemmed Trees, these trees have typically between 3-5 trunks.
4) Pleached trees, are trees usually with a clear stem and then a pleached panel (with branches trained laterally). These can also be pleached to the ground (panels). Pleaching is the same as espalier but the latter is for fruit trees.
5) Roof trees, these have a clear stem and then a square flat (horizontal pleached panel) a top.
6) Cubed trees, a standard stem with a hedged cube atop.
7) Topiary trees, these are trees with clipped canopies (in all kinds of forms) or trained trunks.
8) Hedged - these are feathered trees that have been clipped to form a denser canopy.