Once the succession of Tibetan Gurus and disciples had reached significant proportions, it became popular custom to represent such spiritual genealogies in the form of a cosmic tree uniting all the saints, buddhas and deities of the order concerned. This special kind of Thangka is called in Tibetan language »krung rabs«.
A refuge host field tree is a form that Tibetan Buddhists visualize as present in the sky of inner vision when they meditate at any level of the path.