Most writing about noni is about the juice. This is about the plant, which is more interesting and much less contested.
What it is
The noni tree is Morinda citrifolia, a small evergreen in the coffee family. It reaches perhaps three to ten metres, with large glossy dark-green leaves and small white flowers.
Its range runs from Southeast Asia and the Indian subcontinent across northern Australia and out through the Pacific. It is one of the plants that travelled with Polynesian voyagers, carried deliberately as a useful species, which is why it turns up on islands it could not have reached on its own.
Why it grows where nothing else does
This is the genuinely remarkable thing about it.
Noni tolerates volcanic ground, coral sand, salt spray and drought. It is one of the first woody plants to colonise fresh lava flows in Hawaii. It will grow in ground with almost no soil and in exposure that kills most fruit trees.
That tolerance is why it became a Pacific staple rather than a curiosity: it fruits reliably in places where reliable food is scarce.
It also fruits continuously, all year, with flowers and green fruit and ripe fruit on the same tree at once. For an island food supply that matters more than yield does.
The fruit, and the smell
The fruit is 10 to 18 cm, lumpy, with a pebbled surface, ripening from green through white to a translucent yellowish-white. Inside it is soft and full of small reddish-brown seeds.
It smells strongly and unpleasantly as it ripens, most often compared to a cheese that has turned. The cause is its fatty acids, octanoic and hexanoic acid in particular, which are the same compounds that give some cheeses their character. The comparison is chemically literal rather than a figure of speech.
The taste is bitter and sharp. Almost nobody eats it plain, which is why essentially every commercial noni juice is blended with other fruit.
Its place in Pacific culture
Noni has been used across Polynesia for something on the order of two thousand years, as food, as a dye, and in traditional practice. In Hawaii it is one of the canoe plants, the species early settlers brought with them on purpose.
We are deliberately not going to list what it was traditionally used for. The older version of this article did, at length, and that list is why the article had to be rewritten.
The reason is worth stating, because it applies to every botanical sold as a supplement. A sentence that pairs the words "traditionally used for" with a list of named conditions is read as a claim about the product rather than as history, whatever the surrounding words say. It is the most common way a plant page gets a seller into trouble, and it does not become more accurate for being old.
What is worth saying is that a plant this widely and continuously used, across this many cultures, for this long, is a plant worth studying. That is a real statement and it is where the research interest came from.
What is in it
Noni fruit carries vitamin C, is notably high in potassium, and contains a distinctive group of compounds called iridoids, which are what most of the scientific attention is actually about.
There are several hundred papers on noni, and you can search them yourself rather than take a summary. The honest shape of that literature is the same as for most botanicals: a great deal of laboratory and animal work, much less in people.
If you want the drink rather than the tree, that is Tahitian Noni Juice, including the two safety points worth reading before you buy any.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.
More on this subject: Noni