Hyperaccumulators are one of the most amazing classes of plants on the planet. They have an unusual and rare ability to not just tolerate metal-containing soils, but to take the metals up into the plant’s tissues using them for defense.
One of the more exotic species growing in New Caledonia, on an island of all nickel soil, is so rich in nickel that people say the plant “bleeds” nickel.
Soils formed from ultramafic minerals are typically enriched with nickel and chromium. These minerals are formed from volcanic activity and can generally be found at the surface of volcanic islands, or formed on the seafloor and then brought to the surface through tectonic forces.
The plants above were found on a tropical island off the coast of Australia and New Zealand called New Caledonia, which is an island where the volcanic minerals making it up have weathered down over millions and millions of years releasing significant nickel and chromium into the soils leading to some of the richest nickel soils in the world at over 20%.
Very few plants can tolerate these levels of nickel. That alone would put it in a class of plants that are known as nickel-tolerant, but there is an exciting very rare set of plants that have evolved beyond just the tolerance of the nickel, which can be toxic to most plants, but that instead take the nickel up into their tissues and use it as a deterrent from predators.
The term “hyperaccumulator” was coined by Roger Reeves to describe the extraordinary accumulation of nickel in the tree pictured above, Pycandra acuminata. For nickel hyperaccumulators, the threshold is greater than 1,000 ug/g in the dry leaf, which is a level 100-1,000 times higher than plants not in ultramafic soils, and 10-100 times more than most plants found in nickel-rich ultramafic soils.
The modern definition of a natural hyperaccumulator is one that accumulates 100 times greater than non-accumulator plants
