They take up significant amounts of metal from contaminated soil but their low biomass production tends to limit their phytoextraction ability. As these plants have natural ability to extract metal ions, so it is known as natural phytoex­traction. Hyper-accumulating plants have natural ability to extract high amounts of metals from soil, have efficient mechanism to translocate metals from roots to shoots, and can accumulate and tolerate high metal concentrations due to inherent mechanisms to detoxify metals in the tissues. Metal hyper-accumulators have the extraordinary capacity to accumulate high concentrations of heavy metals in the above-ground biomass. By virtue of this remarkable characteristic, phytoextraction is economically viable alternative to the extreme expense of conventional reme­diation methods [5].

Example: Alyssum lesbiacum as Ni hyper-accumulator, Thlaspi caerulescens/ Alpine pennycress as Zn/Cd hyper-accumulator (Figs. 14.1, 14.2).