Date palms and barley could be stated to be the strongest plants alive, well as far as surviving among toxicity is concerned. Halophytes consist of only 2% of the known plant species and if there was ever a percentage to take on heavy metals it would be a halophyte.
Halophytes can survive in high levels of salinity(salt). They can metabolize toxins and store them in dormant organs. They can also take on soil dryness and extreme salts. Hence how they could survive amongst heavy metal toxins.
read this lovely article below on Halophytes. Happy Phytoremediation!