The koaia grows rapidly in its first few years, typically at a rate of 1 to 1.5 metres per year (2). After a few years the growth rate slows down, but it grows continually unless there is an extended dry period, at which point the canopy broadens and the stems increase in diameter (2).
The koaia starts flowering after two or three years, after which it will flower throughout each year, with a peak in the autumn. The pale yellow flowers provide pollen and nectar for the native insects of Hawaii (2), which are assumed to also pollinate this plant. The koaia produces long pods containing 6 to 12 seeds, and in keeping with its preference for dry conditions, in dry climates the seed quality is high, whilst in wetter climates the seed quality is often poor (2). When ripe, the brown seed pods split open to release the dark brown to black seeds (6).
The roots of this small tree form extensive, shallow, spreading systems which may often be partially exposed at the soil surface (2). The koaia (as a legume) has a special symbiotic relationship with bacteria (Rhizobia) which live in nodules in the plant’s roots. This bacteria is ‘nitrogen-fixing’, meaning it is able to convert the nitrogen in the air to make it available to the plant (2).