BACKGROUNDPlants that accumulate metal and metalloid trace elements to extraordinarily high concentrations in their living biomass have inspired much research worldwide during the last decades. Hyperaccumulators have been recorded and experimentally confirmed for elements such as nickel, zinc, cadmium, manganese, arsenic and selenium. However, to date, hyperaccumulation of lead, copper, cobalt, chromium and thallium remain largely unconfirmed. Recent uses of the term in relation to rare-earth elements require critical evaluation. SCOPE Since the mid-1970s the term 'hyperaccumulator' has been used millions of times by thousands of people, with varying degrees of precision, aptness and understanding that have not always corresponded with the views of the originators of the terminology and of the present authors. There is therefore a need to clarify the circumstances in which the term 'hyperaccumulator' is appropriate and to set out the conditions that should be met when the terms are used. We outline here the main considerations for establishing metal or metalloid hyperaccumulation status of plants, (re)define some of the terminology and note potential pitfalls. CONCLUSIONS Unambiguous communication will require the international scientific community to adopt standard terminology and methods for confirming the reliability of analytical data.

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SUMMARYPlants known as byperaccumulators take up and sequester bigb concentrations of potentially toxic elements from metalliferous soils. We tested tbe hypothesis tbat zinc hyperaccumulation benefits plants by deterring berbivory. In laboratory feeding trials, tbree species of herbivores were allowed to choose between Thlaspi caerulescens (Brassicaceae) plants grown in low-Zn and Zn-amended culture solution. Locusts (Schistocerca gregaria), slugs (Deroceras caruanae), and caterpillars (Pieris brassicae) all showed significant preferences for plants witb lower foliar Zn concentrations. Such differential feeding could result in selection pressures favouring tbe evolution of byperaccumulation. Tbe findings are also relevant to current proposals to exploit byperaccumulation as a means of remediating metal-contaminated soils.