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<div>Ohia, <i>Metrosideros</i> <i>polymorpha</i>, is Hawaii’s most common and widespread native tree, ranging from sea level to 2,500 m elevation in both dry and wet forests. It is the most ecologically important native tree, defining ecosystem function and providing critical habitat to many endemic and endangered flora and fauna. Rapid Ohia Death (ROD) is a newly discovered phenomenon causing widespread mortality of ohia on Hawaii Island. Crowns of infected, mature ohia trees turn yellow, then brown in a matter of days to weeks. Fungal growth occurs within ohia wood with characteristic staining patterns. Greenhouse and growth chamber inoculation experiments on ohia seedlings and saplings have proven that <i>Ceratocystis</i> <i>fimbriata</i> causes ROD. Several genotypes of <i>C</i>. <i>fimbriata</i> were already present in Hawaii, affecting sweet potato, taro, and Syngonium, a common ornamental plant in the family Araceae. The possibility that <i>C</i>. <i>fimbriata</i> from these hosts were the culprit of ROD was examined using pathogenicity tests and phylogenetic analysis and results indicate that no direct link exists. ROD poses a serious threat to Hawaii’s flagship native tree species whose loss would be catastrophic for the diversity, structure, and function of Hawaii’s remaining native forests and the critical services they provide.</div>