A newly discovered plant species accumulates astonishing levels of nickel in its leaves. Concentrations of 18,000ppm by weight, making the dried leaves almost 2% nickel, have been measured. Most plants would die at a thousandth of that level.
Even species that grow in nickel-rich soil seldom have the capacity to hyperaccumulate the metal, although 500 species are known to be able to store large amounts of one metal or another.
A common feature of hyperaccumulators, across distantly related families, is the ability to move metals from the root to leaves where they can hold them without damage. It is thought that the metals serve as a way to stop animals from eating the leaves.
Rinorea niccolifera is the newest entry to the list, discovered by Edwino Fernando of the University of the Philippines and Melbourne University's Dr Augustine Doronila and described in PhytoKeys. It is a tropical forest shrub growing up to 8m tall, so far known only from a small section of north western Luzon. Given the limited sampling it is possible that on different soils it might take in even more nickel.
Nickel is the most common metal for hyperaccumulators to have a taste for, and a handful can store doses even larger than R niccolifera, but some plants with less than a tenth of its capacity are listed as hyperaccumulators.
"Hyperacccumulator plants have great potentials for the development of green technologies, for example, 'phytoremediation' and 'phytomining'" says Dornonila. Phytoremediation is the use of plants to concentrate metals from soil to an extent that the leaves are easier to remove for safe burial than the polluted soil would have been. Phytomining involves the idea that plants could extract commercial quantities of metal from soils where it would not be economic or environmentally suitable to mine them in other ways. Phytoremediation of soils polluted with metals is still in its infancy, while phytomining still theoretical.
Hyperaccumulators generally do not seem to have specialist genes absent from their nonaccumulating cousins, instead they express genes the same genes differently, usually through overexpression of transmembrane transporters. However, we do not yet know if the pattern holds for R niccolifera.