The ombu (Phytolacca dioica) is not really a tree, but a sort of grass. It grows to great age, but since its trunk does not have annual growth rings, its age cannot be exactly determined. Legend has it that the ombu in the Cartuja was planted by Hernando Colón son of the great Admiral Columbus. One of the features of the ombu is its immunity to insects, as its sap is toxic. It grows very quickly to a height of 10 to 15 metres. Its wood is very soft, as it contains a large amount of water, which is necessary to survive the long droughts common in Argentina and Uruguay, where it comes from.