Uptake of nickel by species of Alyssum, Bornmuellera, and other genera of Old World Tribus Alysseae

It has been shown previously that 45 species of Alyssum (Cruciferae), found on serpentine soils, can accumulate nickel to levels above 1000 μg/g (on a dry mass basis). An investigation of most species of the Old World genera of Tribus Alysseae has now demonstrated that this remarkable nickel accumulation is exhibited by five additional serpentine taxa from Turkey and the Balkans: Alyssum peltarioides subsp. virgatiforme, Bornmuellera glabrescens, B. baldaccii, B. tymphaea, and the hybrid B. × petri. All of these taxa had maximum nickel concentrations in the range 1.0-3.1%. Additional data are presented for Alyssum species, including some for taxa not previously reported. Although adaptation by plant species to unfavourable edaphic factors may take place in a relatively short time, it is noteworthy that all species so far recognised as nickel accumulators are from regions that were beyond the maximum advance of the Pleistocene ice-caps. These plants may therefore represent a type of behaviour which started to evolve prior to the most recent glacial episodes. Possible reasons for the endemism of many of the nickel accumulators are outlined.