The discovery and global distribution of hyperaccumulator plants: A personal account

An instance of extreme accumulation of Zn by a plant species was found in the 19th century, and observations of unusually high concentrations of other elements (Cu, Co, Ni, Cd, Pb, As, Se) were recorded between the 1920s and 1970s. Of relevance to the study of ultramafic areas and their floras is the occurrence of extreme Ni accumulation. The term “hyperaccumulator” was introduced in 1976 to signify a species exhibiting a concentration that can be hundreds or thousands of times greater than that usually found in plants on most common soils. Concentration criteria that allow a species to be regarded as a hyperaccumulator have been defined and refined from time to time. The following account details my own involvement in the discovery of new examples of metal hyperaccumulation, with particular emphasis on Ni accumulation by plants of ultramafic floras worldwide. The interest in hyperaccumulators has prompted investigations into different aspects of the biota of metalliferous soils. The search for new examples of hyperaccumulation continues, aided in part by non-destructive X-ray fluorescence scanning of herbarium specimens, which previously served as a resource providing small fragments for sensitive but destructive analysis. Identification of species as hyperaccumulators must be supported by further field exploration to understand the factors governing the level of metal uptake, and to stimulate further work on plant systematics, biochemistry, genetics, and molecular biology. Applications to phytoremediation and agromining are worth pursuing in some cases. Conservation issues are important because many hyperaccumulators are rare and restricted in their distribution.