Native Hawaiian Garden (7722)

Lonomea (Sapindus oahuensis) – getting between the Islands.

There are so many interesting puzzles when one considers the distribution of Hawai‘i’s native plants throughout the Islands. One such puzzle is lonomea, a soapberry tree endemic to only Kaua‘i and O‘ahu. Botanists tell us that about 75% of Hawai‘i’s native flowering plants arrived in the Islands via birds, 23% came floating on the ocean, and 2% were carried by the wind (Carlquist 1967, Ziegler 2002). This generally explains why so many of our native plants have small fruits or seeds. (And, perhaps, why so many of these fruits taste so terrible to us but not to the birds!) Lonomea has a large fruit and seed. It seems unlikely a bird long ago swallowed it, flew to Hawai‘i, and spit or pooped it out. That leaves floating here on the ocean. Viable lonomea seeds sink in water but the fruits, with their trapped air pockets, do float. No one, as far as I know, has determined how long a lonomea fruit will float in seawater. However, we do know that Hawai‘i is far, far away from any other landmass, and, therefore, any fruit that floated here likely had to stay afloat for quite some time. But that, then, is part of the puzzle because if lonomea fruits CAN float a long time, why do we only find lonomea on Kaua‘i and O‘ahu, and not the other Hawaiian Islands? Maybe, because lonomea is a relatively recent immigrant to the Islands? If that first fruit arrived on Kaua‘i, it makes some sense that the next island it would most likely float to would be Kaua‘i’s nearest neighbor, O‘ahu. Okay, but lonomea is the only soapberry tree (there are five to twelve species depending on who you believe) that has simple, not compound, leaves. This suggests (but does not prove) that lonomea is NOT a recent immigrant since it likely took some time for lonomea to evolve into an endemic species with such a unique morphological feature. So, where does that leave us? Well, as I said at the start, with a very interesting puzzle!

Habitat & Appearance: Lonomea is endemic to dry and mesic forests on Kaua‘i and O‘ahu. It is a large tree (20 to 50 feet) with a white truck and branches that sharply contrast its dark green leaves. The small white flowers develop in clusters. Lonomea appears to be self-compatible (http://www.ctahr.hawaii.edu/hawnprop/plants/sap-oahu.htm), so, you only need one tree to produce viable seed. Fruits are oval, about an inch long, and green when immature, turning wrinkled and brown when ripe. The fruit is inedible (to humans). However, because it’s a soapberry, you can cut the fruits up and mix them with water to wash your hair, clothing, etc. Each fruit usually contains a single black, finely-dimpled seed about ½ inch in diameter.

Ripening fruits. Seedlings. Ten-year-old tree. Header photograph of inflorescence courtesy of David Eickhoff CC BY 2.0.

Lonomea in Hawaiian Culture: In ancient times, this tree was called lonomea on Kaua‘i and āulu on O‘ahu. Today, it is commonly referred to as lonomea throughout the Islands. Written records for lonomea and a closely related species, mānele (Sapindus saponaria), are often mixed and remixed, so, it’s difficult to state with certainty how Hawaiians used lonomea. However, lonomea seeds were almost certainly strung into lei (Neal 1965, Krauss 1993), and likely used as a cathartic (Rock 1913). The wood may have also been fashioned into spears (Malo 1951).

Collecting Seeds: Look for ripe lonomea fruit in the fall and winter. The best seeds are those extracted from wrinkled brown fruits still on the tree; avoid green fruits. However, you can often find ripe fruit with viable seed and even good seeds alone on the ground beneath the parent tree. Examine these seeds for any holes and test them in a cup of water; good seeds will sink, and bad seeds will float. Thoroughly wash and sterilize (with 10% bleach for 15 minutes) any seeds you collect from the ground or from fruits on the ground. Lonomea seeds can be stored in the refrigerator for one or two years. After that, I’ve noticed a dramatic drop in their viability.

Growing from Seed: The most effective way of germinating lonomea seeds is still the extracted-embryo method my students and I developed back in 1997. (Refer to the photo-series in Plants from Seed.) Scarify the seeds with clippers or a knife. Place the scarred seeds in clean moist vermiculite for 1 to 2 weeks, or soak them in a shallow pan of water (changing the water daily), until the dark outer seed coat is soft and leathery. Remove the softened outer coat by hand or with clippers. Then, carefully peel off the thin papery brown inner coat. Beneath the inner coat, you will see the cream-colored embryo. Remove the embryo carefully from the remaining outer and inner coats, paying special attention to where the embryonic root is surrounded by the two coats; if you’re not careful, you will break the root. Sow the embryo immediately in clean potting media, burying it about ½ inch deep. The embryo will sprout in about a week. Germination is nearly 100% if you’ve been careful not to damage the embryo. Untreated seeds or seeds that have only been scarred germinate in 1 to 6 months. However, these seeds often rot before they sprout.

Lonomea seedlings grow fast because of the large nutrient stores in their cotyledons. Within three months, the seedlings will be 6 to 8 inches tall and ready for planting. Or, you can be more cautious, repot the lonomea, and wait another three months until the young tree is a foot or more tall. Lonomea seedlings are sometimes attacked by mites. Spray with horticultural oil to control this pest. Occasionally, a seed will sprout and develop into an albino (chlorophyll-deficient) seedling. These seedlings survive for some time until they exhaust the nutrients stored in their cotyledons.

Growing from Cuttings: I have never tried growing lonomea from cuttings. I don’t know of anyone who has.

Growth in the Garden: You should plant your lonomea in a site with full sun to partial shade and lots of surrounding space (i.e., not too close to any other trees). Water the new tree once a week for a few months until it establishes a self-sufficient root system. After that, watering is a matter of choice. Lonomea will grow at a variable rate depending on how much sun and water it receives. If you want a large tree fast, water it often (once a week) and fertilize. Within a year, your tree will be nearly as tall as you; after ten years, it will be a foot or more in diameter and 20-plus feet tall. If you water less (once a month) or not at all, expect your lonomea to grow more slowly (unless, of course, it rains a lot where you’ve planted it). The above watering advice is given with the caveat that the soil surrounding your lonomea drains well. If it doesn’t, you have a problem because lonomea do not like, and will die in, waterlogged soil. Lonomea begin flowering and fruiting after 5 to 10 years. Lonomea makes a great shade tree. While monkeypod trees rain sticky fruits and kukui litter the ground with ankle-busting nuts, the fruits and seeds of lonomea harmlessly disappear and eventually disintegrate into your lawn and soil.

Diseases & Pests: Lonomea has few problem pests. Most common is the occasional attack by borers, both black twig borers and false powderpost beetles. Quickly removing any dead branches is the easiest way to minimize the impact of these beetles. If you still have problems, consider drenching the surrounding soil with a systemic insecticide. The leaves of smaller trees are sometimes chewed by Chinese rose beetles. Fortunately, the leaves on older trees are normally too high for the rose beetles to reach. On rare occasions, whiteflies will infest the underside of some leaves. I have never treated these outbreaks because they have always disappeared on their own.

Ā ā Ē ē Ī ī Ō ō Ū ū