Ok, a bit of mouthful this one.
Acer palmatum (Polymorphum) or Seedling Japanese Maple.
The "seedling"reference is due to this variety of Japanese Maple not being grafted, simply grown from seed. The lack of grafting usually means this Maple is cheaper to buy in nurseries, either potted or as a bare rooted stock in the winter.
A slow grower, this is a small deciduous tree to about 4 mt high and 4 mt wide. It prefers a sheltered position, preferably morning sun and afternoon shade and protection from hot summer winds. Having said that, I have seen this Maple being grown in full sun so they are adaptable, although regular summer watering is key here. The Autumn foliage ranges from yellow, to orange, to red and then purple. This tree is great for small gardens, as a feature tree in a courtyard and can even be grown in a large pot.
Well worth a look.