Many species have been used (either as hyperaccumulators, or as fast growing-high biomass crops) to accumulate metals, thus for their phytoremediation ability. Hyperaccumulators are these plant species, which are able to tolerate high metal concentrations in soils and to accumulate much more metal in their shoots than in their roots. By successive harvests of the aerial parts of the hyperaccumulator species, the heavy metals concentration in the soil can be reduced [23]. According to Chaney et al. (1997) [21], in order a plant species to serve the phytoextraction purpose, it should have strong capacities of uptake and accumulation of the heavy metals when it occurs in soil solution. For example, Sedum plumbizincicola is an hyperaccumulator that has been shown to have a remarkable capacity to extract Zn and Cd from contaminated soils [75]. In addition, a very good also hyperaccumulator for Zn and Cd phytoextraction is Thlaspi caerulescens [23]. Iris pseudacorus L. is an ornamental macrophyte of great potential for phytoremediation, to tolerate and accumulate Cr and Zn [19]. Furthermore, many species of Brassica are suitable for cultivation under Cu and Zn toxicity conditions and may be used for phytoremediation [29]. Phragmites australis, which is a species of Poaceae family, may tolerate extremely high concentrations of Zn, Cu, Pb and Cd, thus can be used as heavy metal phytoremediator [76].

Santana et al. (2012) [20] refer that Genipa americana L. is a tree species that tolerates high levels of Cr3+, therefore it can be used in recomposition of ciliary forests at Cr-polluted watersheds. According to the same authors, this woody species demonstrates a relevant capacity for phytoremediation of Cr. Elsholtzia splendens is regarded as a Cu tolerant and accumulating plant species [77]. Peng et al. (2012) [78] refer that Eucalyptus urophylla X E. grandis is a fast growing economic species that contributes to habitat restoration of degraded environments, such as the Pb contaminated ones. On the other hand, concerning Cd phytoextraction ability, only a few plant species have been accepted as Cd hyperaccumulators, including Brassica juncea, Thlaspi caerulescens and Solanum nigrum. Poplar (Populus L.), which is an easy to propagate and establish species and it has also the advantages of rapid growth, high biomass production, as well as the ability to accumulate high heavy metal concentrations, could be used as a Cd-hypaeraccumulator for phytoremediation [27-28,67]. According to Wang et al. (2012) [28], the increase in total Cd uptake by poplar genotypes in Cd contaminated soils is the result of enhanced biomass production under elevated CO2 conditions. Furthermore, Amaranthus hypochondriacus is a high biomass, fast growing and easily cultivated potential Cd hyperaccumulator [25]. Another species was found to be a good phytoremediator concerning its phytoaccumulation and tolerance to Ni stress is Riccinus communis L. [18]. Finally, Justicia gendarussa, which was proved to be able to tolerate and accumulate high concentration of heavy metals (and especially that of Al), could be used as a potential phytoremediator.

Differences between species, or genotypes of the same species, concerning heavy metal accumulation have been found by many researchers. According to Dheri et al. (2007) [17], the overall mean uptake of Cr in shoot was almost four times and in root was about two times greater in rays, compared to fenugreek. These findings, according to the same authors, indicated that family Cruciferae (raya) was most tolerant to Cr toxicity, followed by Chenopodiaceae (spinach) and Leguminosae (fenugreek). Peng et al. (2012) [78] found that cultivar ST-9 of Eucalyptus urophylla X E. grandis was shown to accumulate more Pb than others of the same species, like ST-2, or ST-29.