|ʻŌhiʻa lehua flowers|
M. p. var. dieteri
Metrosideros polymorpha, the ʻōhiʻa lehua, is a species of flowering evergreen tree in the myrtle family, Myrtaceae, that is endemic to the six largest islands of Hawaiʻi. It is a highly variable tree, being 20–25 m (66–82 ft) tall in favorable situations, and much smaller when growing in boggy soils or 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. ʻŌhiʻa trees grow easily on lava, and are usually the very first plants to grow on new lava flows.
The tree itself is referred to as an ʻōhiʻa tree, and the blossoms are called lehua flowers. This distinction comes from Hawaiian mythology, in which ʻŌhiʻa was a handsome warrior and Lehua was his beautiful lover, and they were transformed into a tree and its flowers, respectively.
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 2,500 m (8,200 ft) 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 400 m (1,300 ft), the tree is also common in seasonally wet forests, where it may be dominant or form mixtures with the native Acacia koa.
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 1,000–3,000 mm (39–118 in) per year is favored, but ʻōhiʻa can grow in dry forests that receive as little as 400 mm (16 in) or bogs that get more than 10,000 mm (390 in) of rain. On moist, deep soils, ʻōhiʻa grows to 20–25 m (66–82 ft) high. Specimens reaching 30 m (98 ft) 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 hāpuʻu (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 reddish brown heartwood 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 kuʻi ʻai (poi boards), weapons, tool handles, hohoa (round kapa beaters), and kiʻi (statues and idols). Although the trunk of ʻōhiʻa was not used to make the kaʻele (hull) of waʻa (outrigger canoes), it was used for their nohona waʻa (seats), pale (gunwales), and pola (decking). Wae (spreaders) were made from the curved stilt roots of ʻōhiʻa. 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 burned hot and cleanly, it was excellent wahie (firewood). The lehua (flowers) and liko lehua (leaf buds) were used in making lei. The flowers were used medicinally to treat pain experienced during childbirth.
There are about 50 species in the genus Metrosideros in Southeast Asia and the Pacific, including four other, much more localized species in Hawaiʻi - M. macropus (lehua mamo), M. rugosa (lehua papa), M. tremuloides (lehua ʻāhihi), and M. waialealae (Wagner et al. 1999). They are easily confused with M. polymorpha, and are best distinguished by 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 Pōhutukawa tree of New Zealand, have been sometimes planted as ornamentals in Hawaiʻi 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.
Metrosideros polymorpha forests in Hawaiʻi have been invaded by a myriad of 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). While ʻōhiʻa itself remains extremely abundant, some species that depend on it such as the ʻakekeʻe (Loxops caeruleirostris) and longhorn beetles in the genus Plagithmysus have become endangered due to shrinkage of forest areas.
The generic name Metrosideros derives from the Ancient Greek metra or "heartwood" and sideron or "iron". The species name polymorpha is also from Ancient Greek, and means "many forms". The Hawaiian language word ʻōhiʻa derives from Proto-Oceanic *kafika, the name of the Mountain Apple tree, Syzygium malaccense, while Lehua derives from Proto-Central Eastern Polynesian *refua, the name of a star, perhaps Antares. The Malay Apple tree has red flowers similar to those of Metrosideros species, and Antares is a bright red star.
In Hawaiian mythology, ʻŌhiʻa and Lehua were two young lovers. The volcano goddess Pele fell in love with the handsome ʻŌhiʻa and approached him, but he turned down her advances. In a fit of jealousy, Pele transformed ʻŌhiʻa 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 ʻōhiʻa 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 ʻōhiʻa tree, the sky will fill with rain representing the separated lovers' tears.
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