Metrosideros polymorpha

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 member of the diverse "Metrosideros" genus, which are widespread over the southwest Pacific.
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 first plants to grow on new lava flows.
"Metrosideros polymorpha" is commonly called a "lehua" tree, or an "ōhia lehua", or simply an "ōhia"; all are correct. There is a widespread but mistaken notion that the Hawaiian word "ōhia" only refers to the tree and that the word "lehua" only refers to its flowers.
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 (pH 3.6-7.4) 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 ("Cibotium" tree ferns), 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. The stomata of the leaves are able to close up in the presence of harmful gases, which gives it an advantage over many non-native trees.
Uses.
The reddish brown heartwood of "M. polymorpha" is very hard, fine textured, and has a specific gravity of 0.7 . In native Hawaiian society, it is used in house and "heiau" construction, as well as to make "papa kui ai" (poi boards), weapons, tool handles, "hohoa" (round "kapa" beaters), and "kii" (statues and idols). Although the trunk of "ōhia" is not used to make the "kaele" (hull) of "waa" (outrigger canoes), it was used for their "nohona waa" (seats), "pale" (gunwales), and "pola" (decking). "Wae" (spreaders) were made from the curved stilt roots of "ōhia". "Pā" (fencing) was made from the wood due to its availability; "kauila" ("Colubrina oppositifolia" or "Alphitonia ponderosa"), more durable woods when in contact with soil, was rarer. As the wood burns hot and cleanly, it is excellent "wahie" (firewood). The "lehua" (flowers) and "liko lehua" (leaf buds) are used in making "lei". The flowers were used medicinally to treat pain experienced during childbirth.
Ōhia lehua is one of the few honey 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 ("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 ʻōhiʻa 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 forest areas shrinking.
In April 2018, the cause of rapid ʻōhiʻa 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.
It is a common misconception that the word "ōhia" is used to refer to the tree and that the word "lehua" refers only to its flowers. "The Hawaiian Dictionary" describes "lehua" with these words:
Thus endorsing the common practice of referring to "Metrosideros polymorpha" as a "lehua" tree, or as an "ōhia lehua", or simply an "ōhia".
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 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 Ōhian 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.