From the perspective of biogeochemical prospecting (i.e. concerning ppb concentrations of Au in plant tissues), Kovalevskii
and Kovalevskaya [5] classified plant species and organs into four
groups:(i) Non barrier bio-objects which give quantitative information on
the Au concentration in the growth medium.(ii) Semi-non barrier bio-objects with high concentration limits of 3–300 times the Au concentration in the growth medium.(iii) Barriers having concentration limits of 3–30 giving only qualitative
information on the concentration of Au in the growth medium.(iv) Background barriers which provide neither quantitative nor qualitative information on Au concentration in the growth medium.