Rare African plant points the way to diamonds

A little-known species of African plant has been discovered that only grows on sites of diamond-bearing rock. The palm-like Pandanus candelabrum apparently prefers soil rich in kimberlite — a type of igneous rock that forms in the Earth's crust in huge vertical columns. These kimberlite pipes, as they're known, reach deep into the mantle and are the result of ancient volcanic eruptions that can push diamonds (along with other material) hundreds of miles up to the Earth's surface. Although geologists have long known that where there's kimberlite, there are often diamonds, now — thanks to Pandanus candelabrum — there's an easy way of finding the kimberlite too.

the kimberlite-rich soil makes a "very good fertilizer"

The discovery of Pandanus candelabrum's expensive taste was made in Liberia by Florida International University researcher Stephen Haggerty, who published his findings in a paper in Economic Geology. Haggerty tells Science, who first reported the story, that he thinks the plant adapted to grow in the kimberlite-rich soil because it contains high levels of magnesium, potassium, and phosphorus. These combine to create what is essentially a "very good fertilizer," says Haggerty. It certainly seems to make for a healthy diet, with Pandanus candelabrum growing up to 10 meters tall on an above-ground root system similar to that of mangrove trees.

Haggerty adds that even though the plant's presence indicates that there's kimberlite in the ground, this doesn't guarantee that there'll be diamonds as well. Kimberlite pipes are rare to begin with, and of the roughly 6,000 examples known in the world, only around 600 contain diamonds. Of these, only 60 or so contain enough gems to be worth mining.

Haggerty, who also works as the chief exploration officer of Youssef Diamond Mining Company, which has mining interests in Liberia, says that if researchers can learn to spot the plant via aerial survey, it could help countries in the area develop new diamond mines without having to fight their way through dense forests. Prospectors, one researcher told Science, are going to "jump on it like crazy."

Indicator species have been used to find metals since medieval times

Pandanus candelabrum's role as a diamond spotter may sound unlikely, but this sort of indicator species has been known about for centuries. For example, the small Alpine plant Lychnis alpina has distinctive pink flowers and has been used since medieval times to find sources of copper. Modern analysis has since discovered that the species is genetically resistant to the metal, allowing it to thrive in soil where the presence of copper ore keeps other plants away.

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