Mesonsidereos, the Javanese Metal-Sapped Tree

Mesonsidereos is a cryptobotanical "metal-sapped" tree with "an iron wire that comes out of the root, and rises to the top of the tree," supposed in some accounts to grow on the island of Java, one of the Greater Sunda Islands in modern Indonesia, formerly the Dutch East Indies. Further to simply possessing a ferrous core, the lore states that any who wear a piece of this tree become themselves impenetrable by iron.

The story of the tree appears in Richard Folkard's Plant Lore (1884), where it is attributed to William Fleetwood, the Bishop of Ely, and his Curiosities of Nature and Art in Husbandry and Gardening, a 1707 English-language translation of Pierre Le Lorrain, l'Abbé de Vallemont's Curiositez de la Nature et de l'Art sur la Végétation; in l'Abbé de Vallemont's work, the story of the tree is, in turn, attributed to Jules-César Scaliger's Exotericarum Exercitationum (1557), a critique of Jérôme Cardan's De Subtilitate (1550), and is plainly stated to have been made as a joke. It is also of note that Scaliger's reference to Java is actually to Greater Java (Java Major), which would have been known from the accounts of Marco Polo, who stated from hearsay that it was the largest island in the world.

Folkard also attributes a detail about the tree having "fruit impenetrable by iron" to Hieronymus Hirnhaim's De Typho Generis Humani (1676).[H]