Accumulation of Nickel and Zinc by Western North American Genera Containing Serpentine‐tolerant Species

Nickel and zinc were determined in 57 taxa of western North American genera containing serpentine‐tolerant species. The studies resulted in the identification of three varieties of Thlaspi montanum (var. montanum, var. siskiyouense, and var. californicum) which are hyperaccumulators (> 1,000 μg/g dry mass) of nickel. These three taxa together with the previously reported Streptanthus polygaloides are the only hyperaccumulators of nickel so far reported for continental America. Significantly higher than normal nickel values (up to 664 μg/g) were recorded for the serpentinophyte Viola cuneata. Elevated zinc levels (> 1,000 μg/g dry mass) were also recorded in four of the Thlaspi taxa and confirm the tendency of many species of this genus to accumulate zinc. It is suggested that hyperaccumulation of nickel by the three varieties of T. montanum is a neo‐endemic rather than palaeo‐endemic process and that the precursor of these varieties is T. montanum var. montanum from non‐mineralized soils.