Noni (Morinda citrifolia) is believed to be among the original
"canoe plants" that Hawaii's Polynesian colonizers brought with
them in their voyaging canoes. The voyagers valued the plant for
its medicine and dyes.

Since the early days of the colonizers noni has become
naturalized on all the main Hawaiian islands. It grows naturally
where it is relatively wet to moderately wet, from sea level to
about 1500 feet elevation. It can be found near the coast, in open
lowlands and grasslands, in gulches, as an early colonizing
plant specie in recent lava flows, in disturbed forests of the dryer
areas, such as the lowland forests in which hala (pandanus)
and kukui nut (Aleurites moluccana) trees grow. It tolerates
salinity and thrives within solution pits, or inland tide pools in
which brackish water (ocean water mixed with fresh water) is
found.

http://www.ctahr.hawaii.edu/ctahr2001/commodities/noni/natural
_habitats.asp