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The Kuli'ou'ou Ridge trail is an important one for native plants on O'ahu because Kuli'ou'ou is the last ridge as you head east down the Ko'olau Range toward Mokapu'u that still has a (small) dominant native forest area on it. The native plant area begins at 1,480 ft. Before you get there you are treated to a wonderworld of forestry plantings and other aliens, with an occasional native if you're alert. Three natives which are more visible than others in the lower ridge area are: 'Ulei (Osteomeles anthyllidifolia)--a low, spreading, woody vine with tiny dark green leaves and beautiful groups of white flowers which look somewhat like white flowers of strawberry plants. You'll see this spreading beside the trail in several spots. Ilima (Sida fallax), the beautiful yellow-orange flowering plant, grows here along the trail, 1-2 ft. tall. You may also be able to pick out some Alahe'e trees (Canthium odoratum). These natives are very slender, straight trees often 10-20 ft. tall. They have small, dark green, very shiny and ornamental leaves with tiny, white, fragrant flowers.
Interesting non-natives you'll see include Noni (Morinda citrifolia)--a very large leaved tree the Hawaiians brought. It easily has the largest leaves of any tree you'll see in the lowland area. It has huge green seed pods that have medicinal value. The tree you see that looks like a Mimosa, with multiple tiny leaves, is the Haematoxylum (Bloodwood). It was imported from Belize. You'll also see lots of feather-needled Ironwoods, Formosan Koa (no Hawaiian koa is on Kuli'ou'ou), plenty of strawberry guava and Christmas berry, and large Cook Pines (sometimes called Norfolk Island Pines) neatly planted for us in rows by the forestry people. A beautiful, dark green-leaved fern that has leaves like fingers of an extended hand is Laua'e (Phymatosorus grossus)--much beloved by Hawaiians, who use it in leis. It sometimes has a lovely fragrance.
Some distance after the trail shelter, you'll encounter a Banyan tree that stands almost as some protective forest guardian. And indeed, when you pass through it, you'll come out into an enchanted area--native Hawaiian forest. Most of the usual native plants, except koa, are here. The forked-branching, thick stands of Uluhe fern (Dicranopteris linearis) confirm you're in a new land. You'll see the large, twining vine, I'e i'e, (Freycinetia arborea)which has a brilliant orange flower in the fall, and huge, corn-on-the-cob like seed pods. The Ohi'a lehua (Metrosideros polymorpha), a sacred tree of the Hawaiians, has red pompom flowers and its branches of small leaves often cluster like little green clouds. Lama (Diospyros sandwicensis) is also common here. It has a slender black trunk, with shiny, olive-green leaves that narrow at the end points. It has beautiful seeds that start green and turn orange or red.
As you head up some stairs nearing the crest, you'll see a huge tree on your left. It looks like a shower tree from downtown Honolulu misplaced up here, but in fact, it's a native rare Ohe (Tetraplasandra oahuensis). It has compound leaves and magnificent yellow star-burst flowers when it's in bloom--look carefully.
After these delights, the summit is somewhat of a letdown, since hikers and birds have brought in many alien pests--Koster's curse (Clidemia) and the purple-flowered Vervain. But you may also see the native yellow daisy (Bidens) in small-flowered version here, as well as the delicate Pala'a (Sphenomeris chinensis)--an elegant native lace fern.
All the natives can be viewed on the UH Botany web page except for the Pala'a fern. The Hawaiian Botanical Society Newsletter, vol. 37, no.3 has a scientific listing of the plants on Kuli'ou'ou for further reference.
Enjoy! Roger D. Sorrell, Ph.D.