Phylogenetic trends in Ni-accumulating plants

The extraordinary uptake of nickel, reaching concentrations of 0.1-5.0% by mass, about 1000 times greater than those usually found in flowering plants, is considered as hyperaccumulation. Between 1948 and 1993, about 190 plant species growing on Ni-rich serpentine soils derived from ultramafic rocks were reported as hyperaccumulators of nickel in various parts of the world. Since 1993, 131 new Ni-hyperaccumulating plants have been detected in the relatively large, ultramafic flora of Cuba, which contains 920 endemic species, all strictly confined to the serpentine areas. Comparative taxonomic studies of the 320 known hyperaccumulators and their relations to non-accumulator serpentine floras has permitted the following observations: hyperaccumulation is concentrated in the dicotyledons; there is a large concentration of hyperaccumulators in Cuba; hyperaccumulation takes more than 1 million years to evolve; nickel concentration does not correlate with accumulation of aromatic substances and volatile oils, is sometimes strongly correlated with infrageneric units, is lacking in groups with a high alkaloid content, is negatively correlated with groups occurring on nutrient-poor soils, and with those manifesting a climbing habit.