Hyperaccumulation of nickel by Alyssum Linnaeus (Cruciferae)

Herbarium specimens of all except one of the 168 recognized species of Alyssum Linnaeus have been analysed for their nickel content in order to identify hyperaccumulators (greater than 1000 microgram per g dry mass) of nickel. A further 31 hyperaccumulators (all in section Odontarrhena) were discovered in addition to the 14 European species reported earlier. Pot trials on the non-accumulator A. serpyllifolium Desfontaines and the hyperaccumulator A. pintodasilvae Dudley in ed. involving addition of nickel to the medium in which the plants were growing, showed that not all species of of section Odontarrhena were able to act as hyperaccumulators of nickel. Hyperaccumulation occurred almost exclusively in the eastern Mediterranean area and Turkey. There appeared to be a definite correlation between species diversity, proliferation and endemism on the one hand, and extremely high nickel concentrations (greater than 1%) on the other. The data have been used to assess the evidence for promoting section Odontarrhena to generic rank.