So how do you tell what's going on inside these plants?
Pycnandra and other hyperaccumulators have been analysed at the DESY synchrotron in Hamburg, using an X-ray technique.
"If you use a conventional microscope you can see structures, but you can't actually tell what it's made out of," explains Dr Kathryn Spiers, who has also been studying Pycnandra.
Dr Spiers used a technique that allows a sample to be imaged and rotated very quickly before it is destroyed by the X-ray beam.
"At the synchrotron the light source is very bright and our detector is very fast, so that means you can [scan it] before you've killed your sample. You see the [samples]; you've literally got a hole burnt across them."
Researchers can then piece together a full image of the plant sample, with its different element components visible.