Puccinia psidii is a rust (a type of plant pathogen) native to Brazil with a very broad host range in the myrtle family (Myrtaceae). Puccinia psidii can have very serious consequences to various species of plants in the Myrtaceae. This family includes guava (the original host of this rust in Brazil), eucalyptus, melaleuca, and a number of species native to Hawaii, including some endemic species (found nowhere else on Earth) and at least one important native forest tree. There are numerous strains of the Puccinia psidii rust—some known to be established in Florida, and at least one reported from California and there is concern that strains may exist or develop that could be devastating to ohia (Metrosideros polymorpha), one of Hawaii's dominant native trees, a foundation species for many remaining Hawaiian native ecosystems. However currently, the major threat of Puccinia in Hawaii is the massive damage it is doing to Eugenia koolauensis, a federally listed endangered species.