The use of plants to decontaminate polluted land, water, or air. Different plant species that are able to grow on contaminated sites have evolved various ways of countering high concentrations of heavy metals, oil, solvents, or other toxic substances. In phytotransformation the plant takes up the toxin and degrades it by enzyme activity, thereby eliminating its toxic nature altogether. In phytostabilization the plant’s root exudates or associated microorganisms precipitate the toxins (e.g. heavy metals) and make them harmless to other organisms. In phytoaccumulation (or phytoextraction) a plant takes up the contaminants and stores them in its tissues; the plant can then be harvested, thus removing the toxin with the plant. A good example is alpine pennycress, which is an effective accumulator of cadmium and zinc. Such plants are termed hyperaccumulators.