Druids and mistletoe harvest according to Pliny the Elder

Upon this occasion we must not omit to mention the admiration that is lavished upon this plant by the Gauls. The Druids—for that is the name they give to their magicians — held nothing more sacred than the mistletoe and the tree that bears it, supposing always that tree to be the robur [oak]. Of itself the robur is selected by them to form whole groves, and they perform none of their religious rites without employing branches of it.