Betula x coerulea (Blue Birch)
Native: Eastern N. America from Nova Scotia south to Vermont
In native environment it often forms a shrub, but may grow to 9m or twice that in cultivation.
Leaves are bluish green, hence the English name.
Flowers are open in May, male catkins 3-5cm long, females about 0.8cm.
Fruits are clustered into a cylinder about 2.5cm long which looks similar to a catkin but which breaks up on September, releasing the winged nuts.