The monarch of native Hawaiian forest trees is the koa. Its height of 50 feet or more and its crown of far spreading branches are attained slowly. It is common on mountain sides, chiefly between altitudes of 1,500 and 4,000 feet, where its round dark green crown is a characteristic feature of the landscape. It is one of the 12 best trees for reforestation. Where growing together under perfect conditions, which seem to be near the higher limit, the trunks are tall and straight for as great a height as 60 feet before any branches begin, and a few reach a diameter of 10 feet. At high altitudes this is especially true today and was also true in the past, as is evidenced by fossils. Lava flowing down the slopes of Mauna Loa buried whole forests, and now near Kilauea Crater, deep well-like holes can be found which are casts of giant koas, the wood of which burned or rotted away long ago. Flows destroyed the trees in ancient times; in modern times, cutting and burning are reducing their numbers even more rapidly. Where growing alone or mixed with lower plants, the koa has wide-spreading branches beginning low down on the trunk.
“The bark is light gray, smooth on young trees, on mature trees considerably furrowed longitudinally. Its smooth, stiff, crescent-shaped “leaves” are broad leaf stems functioning as leaves. Real leaves can be found on young trees and near the base of older ones, and they are finely divided, consisting of five to seven pairs of pinnae, each pinna with 12 to 24 pairs of leaflets. In late winter and early spring, the crown of leaves is lightened by small balls of pale yellow clustered flowers, many of which develop into thin pods.
“Koa wood, used extensively in Hawaii, is called “Hawaiian Mahogany.” When polished it takes a beautiful red through which wavy lines show. Whereas now it is used for furniture, woodwork, ukuleles, and novelties, it formerly was carved by Hawaiians into such things as war canoes, surf boards, and calabashes, and was then as now perhaps the most valuable lumber tree in Hawaii.” — Marie C. Neal, In Gardens of Hawaii, 1965