not reported to have naturalized. Metrosideros polymorpha was originally classified as a variety of M. collina, native to Rarotonga, Tahiti, and other islands of Polynesia, but now is generally accepted as a distinct Hawaiian endemic species. Conservation Metrosideros polymorpha forests in Hawaii have been invaded by myriad alien species. In the wet forests these include the strawberry guava (Psidium littorale), albizia (Falcataria moluccana), and "purple plague" (Miconia calvescens). In drier areas, problematic invaders include faya tree (Myrica faya) and Christmasberry (Schinus terebinthifolius). Alien grasses such as meadow ricegrass (Ehrharta stipoides) may form an understory that prevents or inhibits natural regeneration of the forests. In drier areas, M. polymorpha has to compete with silk oak (Grevillea robusta) and fountain grass (Pennisetum setaceum). Rapid ʻŌhiʻa Death More recently, a strain of fungus initially identified as Ceratocystis fimbriata has attacked the ʻōhiʻa forests of the Big Island, causing Rapid 'Ōhi'a Death. The disease gets this name because healthy trees appear to die within a few days to a few weeks. While ōhia itself remains extremely abundant, some species that depend on it such as the akekee (Loxops caeruleirostris) and longhorn beetles in the genus Plagithmysus have become endangered due to shrinkage of forest areas. In April 2018, the cause of Rapid 'Ohi'a Death was identified as two species of Ceratocystis previously unknown to science: C. huliohia and C. lukuohia. By May 2018, infected ʻōhiʻa trees were found on the island of Kauai, prompting requests that members of the public limit transportation of ʻōhiʻa products within the island. Etymology The genus name Metrosideros is derived from the Greek words metra, meaning 'heartwood', and sideron, meaning 'iron', and refers to the hard wood of the trees in this genus. The specific epithet polymorpha, meaning 'many forms', is very appropriate, since individuals of this species exhibit many different morphologies and inhabit a broad range of ecological situations. The Hawaiian language word ōhia is thought to have been derived from the ancestral Proto-Oceanic word, *kafika. Throughout Oceania, there are many similar-sounding words that were also derived from the same ancestral protoform and, in most cases, they are names for the "mountain apple", or "Malay apple" tree, Syzygium malaccense. In the Hawaiian Islands, however, the word ōhia is not only used to refer to Syzygium malaccense, but also to other species of Syzygium and Metrosideros that occur there. The derivation of the word lehua is more obscure, and