(Xylosma hawaiiense) – Making the task just a bit tougher.

    Maua is a good example of two phenomena that occur frequently with Hawai‘i’s native plants, both making species preservation even more difficult than it already is. The first is the existence of two or more ecotype varieties of the same species. We see this in maua, koa, naio, ‘a‘ali‘i and several other species. Maua grows wild on all the main Hawaiian Islands except for Ni‘ihau and Kaho‘olawe. Here on O‘ahu, I’ve seen maua in mesic forests but never in dry forests. In contrast, on Hawai‘i in Kona and on Lāna‘i at Kānepu‘u, the maua I’ve seen grow in dry forest. The difference between mesic forest and dry forest maua is more than geographic. I have propagated and grown both ecotype varieties and their physiology differ. Simply put, a mesic forest maua does not survive in a dry forest setting (and, I suspect, a dry forest maua would do poorly in a mesic forest).
    The second phenomenon is dioecy, the presence of male pollen-producing and female ovule-producing flowers on separate individuals of the same species. Dioecy in native Hawaiian plants is greater than any other known flora worldwide (Sakai et al. 1995). Maua, ‘ahakea, mēhamehame, and numerous other native Hawaiian plants are dioecious. In ancient times, dioecy was not a problem for these species and probably had adaptive value – maybe, preventing inbreeding depression. However, today, many of these species are rare with individuals widely separated. So widely separated that the pollen from a male plant does not reach the flowers of a female plant. The result is no seeds and no new keiki to ultimately replace the kūpuna plants. Curiously, unpollinated female maua flowers still develop into fruit containing inviable seeds, evidence of the unnatural situation they now find themselves in.

(Top to Bottom) Male (pollen-producing) flowers. New leaves and ripe fruits (photographs courtesy of David Eickhoff). Seedling. Young tree.
Habitat & Appearance: Xylosma hawaiiense is endemic to all the main Hawaiian Islands except Kaho‘olawe and Ni‘ihau. (A second endangered species, X. crenatum, not discussed here, is endemic to Kaua‘i.) Maua grows wild in dry, mesic, and wet forests. It is a medium-size tree up to 40 feet tall with grey bark and shiny green leaves that tend to flutter in the wind. New leaves and stems are a striking reddish-bronze. Flowers develop in clusters along the stems. Male flowers bloom with many stamens; female flowers are without stamens and look like small immature fruit. Berries ripen from green to reddish purple and are about ⅓ inch in diameter.     
Maua in Hawaiian Culture: As with many native hardwoods, Hawaiians fashioned maua into boards or planks (Malo 1951).
Collecting Seeds: Wild maua bear ripe (red to purple) fruits during the summer; cultivated maua may flower and fruit more than once a year. Each fruit holds 1-3 irregularly-shaped, black seeds. After cleaning, test the seeds for viability by dropping them in water; viable seeds will sink either immediately or within an hour. Maua seed can be stored in the refrigerator for at least three years and still remain viable.
Growing from Seed: Fresh maua seed germinate best. After sterilizing the seed in bleach, soak them for about one week in clean water, changing the water daily (see Plants from Seed). The one-week soak seems to hasten and improve the germination. After sowing in a berry container containing vermiculite with sulfur, the seeds take 2-6 weeks to germinate. Seedling growth can be quite rapid (6-8 inches in about three months), particularly, if you use a dilute liquid fertilizer once a week. I have found this species particularly susceptible to broad mites. The mites, invisible to the naked eye, dramatically stunt the growth of seedlings. Infested leaves are distorted and brittle. Eliminate the mites quickly with repeated treatments of sulfur (see Enemies in the Garden). I normally plant out maua seedlings when they reach a minimum of 10 inches in height.
Growing from Cuttings: I have never grown maua from cuttings. Others have reported success in propagating maua from air-layers. This is indeed fortunate since it makes it possible to selectively propagate male or female plants without the years of anxious waiting necessary for seed-grown plants to reveal their sex.
Growth in the Garden: The maua variety I grow regularly is from the dry woodlands of Kona, Hawai‘i; it grows best in full sun and poorly in shade. While this variety has good drought tolerance, it should be watered regularly (once a week) for several months after planting. During the cooler winter months, new plants can grow quickly, often branching low down on the main trunk. This is a good time to apply fertilizer to further hasten growth. A support pole can help prevent toppling or broken branches during strong winds. After two to three years of good growth, you should have a small tree 3-5 feet tall. This is when flowering starts and you discover if you have a male or female plant. Obviously, if you intend to harvest seed from your maua (to give to all your friends, of course), you’ll need to plant more than one and be lucky enough to have at least one male and one female tree. Maua often grow slower after they start flowering. However, because larger maua are more resilient than smaller trees, I encourage you to promote maximum growth with regular (but not extreme) fertilizing.   
Diseases & Pests: Larger (two feet tall or more) maua are less bothered by broad mites. Still, keep watch for any symptoms of infestation. Root mealybugs can be a serious problem and should be dealt with quickly (see Enemies in the Garden). Black twigborers can kill young maua or the branches of older trees. These attacks can be severe during times of stress caused by drought, inadequate light, or another pest. Over the years, I have lost several maua within weeks to, I think, a soil-borne fungus (or bacterium). Changes in watering (both increasing and decreasing) have preceded some of these quick deaths, so, the best advice I can currently give is proceed slowly with any changes in irrigation.
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