The switchbacks up Kealia are a very special place for Hawaiian plants. This dusty and difficult environment at first sight seems uninteresting and inhospitable (except for the spectacular views), but its very ruggedness preserved great dryland Hawaiian plants which seldom occur in such numbers or with such accessibility elsewhere on O'ahu.
First, look for a low, viney plant, spreading close to the ground, beginning as early as 3-4 switchbacks into the trail. It will have beautiful little white trumpet-shaped blossoms, slightly purple-tinged. Its leaves are roundish with blunt ends. This is the Hawaiian Plumbago (Plumbago zeylanica, 'Ilie'e). It is pictured on the UH Botany web pages, and in Sohmer and Gustavson (Plants and Flowers of Hawaii), p. 63. It is common on this trail; seldom seen in such numbers elsewhere due to habitat destruction.
Two Hawaiian dryland trees easily seen here are the Soapberry (Sapindus oahuensis, Lonomea), and the Wiliwili (Erythrina sandwicensis). Both are pictured on the UH Botany web pages. The Soapberry has big, deep green, long, glossy leaves, narrow at the tips, and occurs both as big trees and keiki on the trail. The Wiliwili is very different. While it also occurs as big trees and keiki, it has many unusual characteristics which really set it apart. It has very light, yellowish bark. Its leaves are light green, big, and roundish. It has spectacular red or orange flowers, and seed pods which hang down and are long and twisting (thus, "wiliwili"). Its seeds are large and brilliant cream-red. This trail currently preserves probably the most native Wiliwili's on O'ahu, since on many other dryland trails they have been destroyed by fire. Both the Wiliwili and Soapberry occur in some numbers at the middle level of the switchbacks, with the Wiliwili's continuing up to the shelter at the top.
Lastly, the spectacular yellow daisy (Bidens torta, ko'oko'olau) on this trail also is native and hard to find elsewhere in such numbers. The blossoms are large--around 2 or 3 inches across. The Hawaiians made a medicinal tea out of the leaves. There are many native yellow daisies in Hawaii, but the kind on this trail is definitely the most spectacular. You'll begin to notice it mid-way up the trail and it continues up to the top of the switchbacks.
Other, rarer plants for the experts to note: the Schiedea kealiae (a Carnation relative, pictured in the UH Botany pages), Sicyos hispidus (a big-leaved vine, in the UH pages), and one Hao tree (a Plumeria relative, Rauvolfia sandwicensis), in the UH pages.
Aloha, and enjoy the plants and views!
Roger Sorrell, Ph.D.