Flowers of Hawaiʻi Island form. (Header photograph shows flowers of Oʻahu form.) A rIpe uhiuhi fruit/pod normally holds one to three seeds. Only a few years old, this cultivated uhiuhi is already flowering. An old mature wild tree under the care of the Waikōloa Dry Forest Initiative. This false powderpost beetle above its hole can quickly kill a young uhiuhi. In defense, a healthy uhiuhi will release a sap that fills the hole and hardens.

Growth Requirements

General

    Mezoneuron kavaiense is best displayed as an accent plant in the ground and tends to do poorly as a container plant. This is because its roots quickly circle the bottom of the pot, thicken, and eventually kill the plant (i.e., extreme root-binding). If it is necessary to keep your uhiuhi in a container for an extended period (i.e., six months or more), tall square pots (e.g., treepots) are best.

    Interestingly, while uhiuhi seedlings/saplings exhibit the problem above, they do not grow a massive root system that fills their pot. In fact, often when removing a sapling from a pot for planting, much of the media will fall away, leaving the roots exposed. To prevent this from happening, Bill Garnett suggests growing uhiuhi with a companion native plant with a fibrous root system, such as a native grass or koʻokoʻolau (Bidens spp.), in the same pot. The companion plant will create a root mass that encompasses the uhiuhi roots and make transplanting into the ground less damaging and stressful for the uhiuhi [Garnett 2014].

    Plant your uhiuhi in the ground when it is young (i.e., a foot or less tall). Make sure the site has good drainage and avoid disturbing the roots as much as possible when planting; consider Bill Garnett's solution (above) to achieve this. While you should choose a sunny site in the landscape for the uhiuhi, new plantings survive better if you also construct a temporary structure to provide it with shade, particularly during midday.

    For the first few months after planting, uhiuhi appear to stop growing, at least above ground. We suspect the young plant is diverting all its energy into new root growth, or waiting for beneficial microbes such as mycorrhizae fungi to become associated with its roots. However, we have never dug up a young uhiuhi to test this hypothesis. (Consider inoculating the seedling while it is still in a pot with soil from beneath a mature tree to hasten this period.) Be patient and water but don’t overwater (i.e., just enough to avoid wilted leaves) the uhiuhi during this stasis. 

    Following this slow-growth period, uhiuhi grow rapidly and can be over five feet tall in a year. At this stage, your young tree should require little to no watering, and you should water it only when there are visible signs (e.g., wilted leaves) of drought-stress. Also at this time, it is common to have multiple large branches develop and for the young tree to become top-heavy. This is a problem since often the branches will break or the entire tree will uproot and fall over because of strong winds. You can reduce the chances of this happening by planting the uhiuhi among taller trees which will protect it from strong winds. Pruning too, can help prevent serious damage; remove one or more of the multiple large branches to force the tree to devote all its energy to developing one thickened trunk.

    Mezoneuron kavaiense begins flowering and setting fruit after one to three years in the ground. Be smart and collect and store this early seed in case your young tree meets an unnatural end. After reaching about ten feet in height, uhiuhi grows more slowly, possibly because more and more energy is being diverted to flowers and fruits and increasing the girth of its trunk(s) and branches.

Pests and Diseases

    Mezoneuron kavaiense is deceptively difficult to keep alive. We have grown and maintained a few uhiuhi for more than five years, as have others. But many more young trees have died under our care (or, more properly, have died because of our insufficient care). Young uhiuhi are targets for several insect pests, sometimes with fatal consequences. Scale insects, particularly hibiscus snow scale, frequently attack small uhiuhi, and, if left untreated, can kill young trees. Repeated spraying with horticultural oil, a systemic insecticide, or both can eliminate the scale. The black twig borer can deliver a fatal hit to uhiuhi less than two feet tall. Taller uhiuhi are also attacked, but usually only side branches are killed; when the main truck is killed, new sprouts appear below the borer holes. Refer to the Pests & Diseases page for ways to minimize black twig borer attacks. Other borers, such as the false powderpost beetle, can quickly kill both small and quite large uhiuhi if they are drought-stressed. (This beetle once killed one of my (Koebele) six-foot-tall uhiuhi in less than a week!) Interestingly, less stressed uhiuhi (and lonomea) will defend themselves by producing a sticky sap that quickly fills the borers’ holes and hardens.

Special Features and Information

General

    Fabaceae contains numerous agriculturally important plants, and is the third-largest land plant family in number of species, behind only the Orchidaceae and Asteraceae, with about 765 genera and nearly 20,000 known species [WikipediA;Fabaceae].

    Mezoneuron kavaiense wood is extremely hard, durable, and dense, so much so that it sinks in seawater. It is often very dark — even black — but I (Koebele) have also seen nearly white uhiuhi wood.

Hawaiian Name

    Kāwaʻu and Kea are names for Mezoneuron kavaiense on Maui [Wagner et al. 1990]. Kāwaʻu is also the name for two other native Hawaiian plants, Ilex anomala and Leptecophylla tameiameiae. Hillebrand in 1888 recorded the name kolomona for this species. However, this is likely a post-contact name given to uhiuhi because its leaves, flowers, and pods are similar to those of the introduced shrub Cassia surattensis, also called kolomona [Medeiros et al. 1998]. In some publications, uhiuhi is spelled as two words, uhi uhi, or with an ʻokina, ʻuhiuhi or uhiʻuhi. However, it is most often spelled as uhiuhi, one word without an ʻokina.

Etymology

    The former genus, Caesalpinia, honors Andrea Cesalpino (1519-1603), an Italian botanist, philosopher, and physician to Pope Clement VIII [Wagner et al. 1990]. The current genus name, Mezoneuron, is from the Greek meizon, meaning "greater," and neuron, meaning "nerve," referring to the plant's winged pod [Gagnon et al. 2016]. The species name, kavaiense, is in reference to the island of Kauaʻi, one of the islands where this tree is naturally found. The suffix -ense added to Kauaʻi to form a geographical epithet [Gledhill 2008].