Metrosideros polymorpha, the ōhia lehua, is a species of flowering evergreen tree in the myrtle family, Myrtaceae, that is endemic to the six largest islands of Hawaii. It is a highly variable tree, being tall in favorable situations, and a much smaller prostrate shrub when growing in boggy soils or directly on basalt. It produces a brilliant display of flowers, made up of a mass of stamens, which can range from fiery red to yellow. Many native Hawaiian traditions refer to the tree and the forests it forms as sacred to Pele, the volcano goddess, and to Laka, the goddess of hula. Ōhia trees grow easily on lava, and are usually the very first plants to grow on new lava flows. It is a common misconception that the wordōhia is used to refer to the tree and that the word lehua refers only to its flowers. The Hawaiian Dictionary defines lehua with these words: "The flower of the ōhia tree... also the tree itself ." Thus the Metrosideros polymorpha may be referred to correctly as a lehua tree, or as an ōhia lehua, or simply an ōhia.
Distribution
Metrosideros polymorpha is the most common native tree in the Hawaiian Islands, tolerating a wide range of soil conditions, temperature, and rainfall. It grows from sea level right up to the tree line at elevations of and is commonly found in moist and dry forests, high shrublands, and is a colonizer of recent lava flows. It is relatively slow growing. Dominant in cloud forests above, the tree is also common in seasonally wet forests, where it may be dominant or form mixtures with the native Acacia koa.
Habitat
Metrosideros polymorpha may occur as a tall tree or a prostrate shrub, and everything in between. Preferred soils are acidic to neutral and either a Histosol, Mollisol, Podsol, Oxisol, Ultisol, or Alfisol. Rainfall of per year is favored, but ōhia can grow in dry forests that receive as little as or bogs that get more than of rain. On moist, deep soils, ōhia grows to high. Specimens reaching high are on record. The trunk varies in form. In some trees, it is straight and smooth; in others, it is twisted and prominently fluted. Trees growing in forests often have stilt roots, having germinated on logs or the stems of fallen hāpuu, which have long decayed away when the tree has reached maturity. Some trees have fibrous aerial roots to gather moisture. At high elevations, and in areas with poor soils or little rainfall, shrub forms are the norm. Flowers are usually bright to medium red but orange-red, salmon, pink, yellow, or orange forms are also found. The flowers appear in clusters on the terminal ends of the branches. Masses of stamens extend from the flower and give the blossoms their characteristic pom-pom shape.
Uses
The reddish brownheartwood of M. polymorpha is very hard, fine textured, and has a specific gravity of 0.7. In native Hawaiian society, it was used in house and heiau construction, as well as to make papa kui ai, weapons, tool handles, hohoa , and kii. Although the trunk of ōhia was not used to make the kaele of waa, it was used for their nohona waa, pale, and pola. Wae were made from the curved stilt roots of ōhia. Pā was made from the wood due to its availability; kauila, more durable woods when in contact with soil, was rarer. As the wood burned hot and cleanly, it was excellent wahie. The lehua and liko lehua were used in making lei. The flowers were used medicinally to treat pain experienced during childbirth. Ōhia lehua is one of the fewhoney plants that is native to the Hawaiian Islands.
Similar species
There are about 50 species in the genus Metrosideros in Southeast Asia and the Pacific and as well one species in South Africa. The Hawaiian Islands are home to five species of Metrosideros that are endemic to the islands, meaning they are found nowhere else in the world. These are: Metrosideros polymorpha,M. macropus, M. rugosa, M. tremuloides, and M. waialealae. The species are readily distinguished from one another by the characteristics of their leaves. Metrosideros kermadecensis, from the Kermadec Islands north of New Zealand, has recently become naturalized on Maui and may become a pest species. Several cultivars of M. excelsa, the pohutukawa tree of New Zealand, have been sometimes planted as ornamentals in Hawaii but are 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, albizia, and "purple plague". In drier areas, problematic invaders include faya tree and Christmasberry. Alien grasses such as meadow ricegrass may form an understory that prevents or inhibits natural regeneration of the forests. In drier areas, M. polymorpha has to compete with silk oak and fountain grass.
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 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 nameMetrosideros 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 while there are many opinions regarding its origin, there has been, to date, no historical linguistic study of the word to provide convincing evidence for any particular etymology.
Mythology
In Hawaiian mythology, Ōhia and Lehua were two young lovers. The volcano goddess Pele fell in love with the handsome Ōhia and approached him, but he turned down her advances. In a fit of jealousy, Pele transformed Ōhia into a tree. Lehua was devastated by this transformation and out of pity the other gods turned her into a flower and placed her upon the ōhia tree. Other versions say that Pele felt remorseful but was unable to reverse the change, so she turned Lehua into a flower herself. It is said that when a lehua flower is plucked from an ōhia tree, the sky will fill with rain representing the separated lovers' tears.
