Native Hawaiian Garden (7722)

Keahi (Sideroxylon polynesicum; formerly Nesoluma polynesicum) – Hawaiian SuperGlue

The first time I saw a keahi was within the amazing windswept dry forest at Kānepu‘u, Lāna‘i. I was there on contract for The Nature Conservancy of Hawai‘i to determine the best germination methods for some of the forest’s more common native tree species. Knowing little about this smallish tree, I eagerly collected the shiny black fruits – with my bare hands. On the flight back home to O‘ahu that afternoon (and, after repeatedly washing and rinsing my hands), I realized the folly of my behavior. Everything I touched felt like it was made of scotch tape – it was absolute torture!

While no ancient uses of keahi are documented, it’s my bet Hawaiians of old made good use of its sticky fruits. Kia manu (bird-catchers) would smear ‘ulu (breadfruit) sap or the fruits of pāpala kēpau on a branch frequented by Hawai‘i’s colorful native birds. This would hold the bird’s feet to the branch while the kia manu plucked the desired feathers. The bird was then released to eventually grow back the lost feathers. It was an excellent way for Hawaiians to make sure there would always be a supply of this valuable commodity.

Today, no one catches birds, native or otherwise, with ‘ulu sap, pāpala kēpau or keahi fruits. However, with its rust-colored leaves that seem nearly impervious to insect damage, keahi is still an attractive addition to any native garden.

Habitat & Appearance: Keahi grows in dry forests on all the main Hawaiian Islands except Kaho‘olawe and Ni‘ihau. It is also found in the Austral Islands. However, today, the tree is rare throughout its range. Most of the keahi I’ve seen are not very tall (less than 15 feet). However, there are exceptions, including one very tall (about 40 feet) now-dead tree I came across in Nānākuli Valley. The young branches, stem-tips and undersurface of the leaves are covered with rust-colored hairs. Flowers are small and greenish-white. Keahi fruits look like small olives turning from green to dark purple or black when ripe.

Keahi leaves and ripe fruit. Ripe fruit with sap. Seedlings. Mature tree at Maui Nui Botanical Garden. (Mature tree and header photographs courtesy of Forest & Kim Starr CC BY 2.0)

Keahi in Hawaiian Culture: See above.

Collecting Seeds: In cultivation, keahi flower and fruit repeatedly throughout the year. (I haven’t seen enough wild keahi to tell you if they flower and fruit more than once a year.) Collect the fruits when they are very dark purple or black; be smart and wear gloves when collecting! Keep the ripe fruits together and moist in a partially-closed plastic bag at room temperature for 1-3 weeks until they become soft (and often moldy). By this time, most of the sticky fruit sap will have degraded. Still, to be safe, clean the seeds under running water in a sink. While cleaning, you’ll discover a thin, translucent shell surrounding the seed; remove it with your fingernail or a pair of forceps. I have always used relatively fresh seeds, no more than 6 months old, when growing keahi. Therefore, I can’t tell you how long they’ll remain viable stored in the refrigerator or freezer.

Growing from Seed: This is one of the few native plants that sprouts better for me using Method Two rather than Method One. With Method One, I often get little germination or the seeds will rot. In contrast, under the less sterile conditions of Method Two, the seeds sprout consistently 1-2 months after sowing – go figure! Perhaps, it’s the daily watering on the shadehouse bench, the day-night temperature fluctuation being outside, or it has something to do with natural versus artificial light. (Some day I’ll have the time to conduct the proper experiments to figure this out.) Few pests attack the seedlings with the exception of broad mites; see Enemies in the Garden to deal with these guys. In cone-tainers, the keahi grow 1-2 inches per month when fertilized (Miracle-Gro® once a month); growth is much slower without fertilizer. After reaching 10 inches, the keahi can be planted in your garden.

Growing from Cuttings: The few times I’ve tried, I’ve never been successful at getting keahi cuttings to root.

Growth in the Garden: Once in the ground, keahi grow at a moderate pace of one to two feet a year until the tree starts flowering. This usually starts in the third or fourth year and, in my experience, slows upward growth. All my keahi had short (less than ten feet tall) parents, and they, likewise, have remained short after more than fifteen years. According to the Manual of the Flowering Plants of Hawai‘i (Wagner et al. 1990) and other taxonomic sources, keahi have unisexual flowers and the plants are dioecious (separate male and female trees). However, the Manual also suggests that some trees may have (some) perfect flowers. This appears to be the case with all the keahi I’ve encountered since every keahi I’ve ever seen bore fruit with some trees regularly producing many fruits while others produced only a few.

Diseases & Pests: No diseases and only two pests, the black twig borer and scale insects, have ever attacked my keahi. The borer damage has always been slight, one or two branches, so, I’ve never resorted to any type of treatment. Refer to Enemies in the Garden if scale insects or black twig borers become a problem with your keahi.

Ā ā Ē ē Ī ī Ō ō Ū ū