Leylandii or Leyland Cypress, Cupressocyparis leylandii, is the world's most vigorous coniferous tree. A Leylandii hedge is great for creating privacy in a hurry and a row of mature Leylandii trees can easily conceal a ten storey house. It has quite a narrow, evergreen canopy and mature, unclipped plants have a columnar shape. Leylandii can grow up to about 40 metres high and it should get there in less than 40 years. Leylandii is great for really tall screening.