The grey poplar tree in Birr Castle Estate is the largest grey poplar in both Ireland and Britain. It is considered to be a natural hybrid of our native aspen and the white poplar of continental Europe and Asia. This is an excellent example of how two smallish trees got together and created a monster that has far outgrown its parents. Offaly people are very proud of their grey poplar tree and they believe it is possibly the largest of its kind in the world. For many it is an astonishing landmark, a meeting place and the symbol of a great arboretum in the heart of Ireland.