Petrobium
 Petrobium is a monotypic genus in the family Asteraceae endemic to the island of Saint Helena in the South Atlantic Ocean. The vernacular name is Whitewood.Petrobium arboreum R.Br. (Saint Helena Whitewood) is found in the tree-fern thicket at the top of the central ridge of Saint Helena. Individuals are either female or hermaphrodite i.e. the species is gynodioecious.