Answer: Sunflowers

Phytoremediation is the process of using plants to restore balance to an environment damaged by natural or man-made events. A subset of the broad category of phytoremediation is rhizofiltration, wherein the root systems of plants are used to filter, via the movement of water in the soil and the uptake of water by the plants, toxic substances and excess nutrients held in the soil.

Among the various plants used for rhizofiltration, sunflowers have proven to be particularly effective at the task. They grow rapidly and they’re very tall; their height and mass necessitate a strong and broad root system. Further, sunflowers have proven to be particularly efficient at drawing heavy metals and radioactive isotopes up into their biomass. By planting thousands of sunflowers at the site of radioactive disasters (such as Chernobyl and Fukushima), radioactive material can be harvested from the ground without massive excavation efforts. The resulting sunflower plants are then treated as radioactive waste and handled like the soil would be (but much more efficiently).

This is also, uncoincidentally, why the sunflower is the international symbol for nuclear disarmament.