Lehua mamo in its natural habitat in the Koʻolau Mountains. A cultivated, uncommon red-flowered form.

Growth Requirements

General

    Lehua mamo requires rich organic soil with excellent drainage to do well. Though it does need bright light, it appears not to be very tolerant of the strong afternoon sun when planted out as a sapling, as is ʻōhiʻa (Metrosideros polymorpha). So best to choose your planting locations wisely and protect it from harsh sunlight until it is established. In my (Eickhoff) experience, M. macropus has been more sensitive to planting in permanent sites in the ground than M. polymorpha. So take extra care with this species. A few planting guidelines can help: Dig a larger planting hole than the root ball, perhaps as much as twice as large. Put good drainage material, such as black or red cinder, in the bottom. When planting lehua mamo, never splay out the root ball, but gently place it in the hole as is. Nor should it be planted too deeply. Soil should never cover the surface area around the trunk base. Better to err on the side of planting too high than too low. Water the soil thoroughly. A final watering of B-vitamin solution may help to alleviate stress and encourage new root growth. For small plants, water every day until established; for larger plants, every two or three days should suffice. Signs of liko, new leaves, are a key to a successful planting.

    For container-grown lehua mamo, ensure there is adequate drainage by using black cinder. Fertilize at half strength as directed and avoid letting the plant become root-bound in pots. It is best to transplant them into the ground before this occurs.

    When necessary, it is recommended to perform light and careful pruning on trees and shrubs, as this will not harm them. It is important to avoid excessive pruning at any one time. Take your time and prune over several weeks or months.

Pests and Diseases

    Caterpillars and Chinese rose beetles can wreak havoc on new growth. The black twig borer is a particularly troublesome pest. When dealing with infected material, it is crucial to cut well below the dead area, wrap it securely in a plastic bag, and dispose of it immediately. Whiteflies, along with black sooty mold, can also infest the trees.

    Lehua mamo is vulnerable to attacks by the bright yellow ʻōhiʻa rust, also known as guava rust (Puccinia psidii), especially in wet environments or during the rainy season. This aggressive rust can become a serious issue if not addressed promptly. At the first sign of ʻōhiʻa rust, it is important to carefully trim off the infected material, securely bag it, and dispose of it. One recommended method is to place the cut pieces in a bottle with a small amount of alcohol before disposal. Additionally, the affected plant and any nearby relatives (Eugenia spp., Syzygium spp.) should be treated with a fungicide immediately. Be sure to clean your tools with alcohol after trimming infected tree parts so as not to spread it to other plants. And, it is crucial to never add trimmings damaged by ʻōhiʻa rust or black twig borer to a compost pile.

    Rapid ʻŌhiʻa Death (ROD) is a severe and deadly fungal disease that rapidly kills ʻōhiʻa trees, though I (Eickhoff) do not know if it has affected lehua mamo (M. macropus) to any degree. But this devastating disease is caused by two aggressive fungi, Ceratocystis lukuohia and C. huliohia. Interestingly, the specific epithet lukuohia means to "massacre, destroy, slaughter, lay waste, devastate, exterminate, ravage" ʻōhiʻa; huliohia means to "turn, change, affect, overturn, convert, reform" ʻōhiʻa [Hawaiian Dictionaries]. DO NOT move ʻōhiʻa, or any parts of it, including lei, between islands. Refer to the Pests & Diseases page for treatments.

Special Features and Information

General

    Lehua mamo (Metrosideros macropus), belonging to the Myrtle family or Myrtaceae [Nature Clearly], is a diverse group with over 5,950 species. In Hawaiʻi, several non-native relatives that have become naturalized, such as myrtle, tea tree, strawberry guava (waiawī ʻulaʻula), pineapple guava (kuawa), allspice, eucalyptus, melaleuca (paper bark), bottlebrush (Callistemon spp.), and Surinam cherry (Eugenia uniflora). Unfortunately, some of these non-native species have become invasive, displacing native forests and creating monocultures that stifle biodiversity. One particularly invasive species is the strawberry guava (Psidium cattleianum), which forms dense canopies that prevent other vegetation from growing beneath it.

    Among the native Metrosideros species in Hawaiʻi, there are five endemic species: Lehua ʻāhihi or ʻāhihi (M. tremuloides), lehua papa (M. rugosa), and two species known as ʻōhiʻa (M. polymorpha and M. waialealae), with M. polymorpha being the most common and widespread in the islands.

    As a key component of native Hawaiian forests, ʻōhiʻa (Metrosideros spp.) often stands as a dominant or co-dominant tree. The number of natural habitats where ʻōhiʻa grows is simply staggering! Trees and shrubs can be found in or near coastal sites, dry, mesic and wet forests, wind-swept slopes and ridges, arid shrublands, sub-alpine, and even saturated mountain bogs perpetually shrouded by mist, where mature flowering ʻōhiʻa may grow only a few inches tall. They can even be commonly seen growing as an epiphyte on hāpuʻu (tree fern). ʻŌhiʻa are often the first to establish themselves on new lava flows, creating a welcoming environment for a variety of plants and animals seeking refuge. Their adaptability and resilience make them a vital part of Hawaiʻi's unique ecosystem.

Hawaiian Name

   Lehua is the flower of the ʻōhiʻa tree, but also the tree itself Hawaiian Dictionaries. Lehua mamo is named for the Hawaiʻi mamo or hoa (Drepanis pacifica), an extinct honeycreeper known for its prized yellow feathers [Pratt 2005]. ʻŌhiʻa is the collective name for all the Hawaiian Metrosideros species (macropus, polymorpha, rugosa, tremuloides, waialealae) Hawaiian Dictionaries. 

Etymology

    The generic name Metrosideros is derived from the Greek metra, heartwood (Lit., heart of iron), and sideron, iron, referring to the very hard wood of these plants [Gledhill 2008]. The specific epithet macropus means big foot, referring to the large leaves and long leaf petioles [Gledhill 2008].