Nickel Uptake by Californian Streptanthus and Caulanthus With Particular Reference to the Hyperaccumulator S. Polygaloides Gray (Brassicaceae)

The nickel content of herbarium specimens of Californian Streptanthus and Caulanthus has been determined. Serpentine‐tolerant species had nickel values of 10–100 μg/g (dry mass) except in the case of S. polygaloides Gray which had nickel values in the range 3,300–14,800 μg/g (0.33%–1.48%). This is the first hyperaccumulator of nickel found in the Americas. It is suggested that the later classification of S. polygaloides as the monotypic Microsemia polygaloides (Gray) Greene may be justified if the nickel accumulation data are used to reinforce the existing marked morphological differences from other Streptanthus.