Topiary is the horticultural practise of training live perennial plants by clipping the foliage and twigs of trees, shrubs and subshrubs to develop and maintain clearly defined shapes. The term also refers to plants which have been shaped in this way. As an art form it is a type of living sculpture. The plants used in topiary are evergreen, mostly woody, have small leaves or needles, produce dense foliage, and have compact and/or columnar growth habits.