All plants absorb essential minerals, including iron, manganese, and zinc. But heavy metal overdoses are hardly essential. They oviposit, or lay eggs, on both. High-metal plants poison unwelcome caterpillar guests. Researchers are less certain about hyperaccumulator biology.
Nobody knows yet.
We've got to do the basic research to find out. One thing is certain. Among metal-munchers, nickel is the toxin of choice. Of the roughly 400 known hyperaccumulators, more than 300 absorb nickel. The next favorite, cobalt, attracts 26 known hyperaccumulators.