The name koa in the Hawaiian language ultimately comes from Proto-Austronesian *teRas meaning "core" or "ironwood"; many names referring to certain ironwood or heartwood species in Southeast Asia and Oceania such as Vitex parviflora (tugás in Cebuano), Eusideroxylon zwageri (togas in Tombonuwo), and Intsia bijuga (dort in Palauan) descend from this root.

[8] Initially, bipinnately compound leaves with 12–24 pairs of leaflets grow on the koa plant, much like other members of the pea family.

[9] Koa is endemic to the islands of Hawaiʻi, Molokaʻi, Maui, Lānaʻi, Oʻahu, and Kauaʻi, where it grows at elevations of 100–2,300 m (330–7,550 ft).

Acidic to neutral soils (pH of 4–7.4)[6] that are either an Inceptisol derived from volcanic ash or a well-drained histosol are preferred.

[4] Koa and ʻōhiʻa lehua (Metrosideros polymorpha) dominate the canopy of Hawaiian mixed mesic forests.

[12] The koa's trunk was used by ancient Hawaiians to build waʻa (dugout outrigger canoes)[13] and papa heʻe nalu (surfboards).

Trey Anastasio, guitarist for the band Phish, primarily uses a koa hollowbody Languedoc guitar.

[23] Genetic sequence analysis results announced in 2014 confirmed this close relationship; the estimated time of divergence is about 1.4 million years ago.

[25] A closely related species, koaiʻa or koaiʻe (A. koaia), is found in dry areas.

Many wet forest areas, where the largest koa grow, have been logged out, and it now comes largely from dead or dying trees or farms on private lands.

[10] Experiments at the Hakalau Forest National Wildlife Refuge have shown that ʻōhiʻa lehua (Metrosideros polymorpha) survives best in pasture when planted under koa.

This is because koa trees reduce radiative cooling, preventing frost damage to ʻōhiʻa lehua seedlings.

[26] Koa is the preferred host plant for the caterpillars of the green Hawaiian blue (Udara blackburni), which eat the flowers and fruits.