Option-wise explanation

1. Poaceae

• Grasses such as Phragmites, Vetiveria, and Miscanthus are important for phytostabilization and some metal uptake, and are increasingly studied.​

• However, historically and quantitatively, they are not the family “most extensively used” in phytoextraction research compared with Brassicaceae.

2. Brassicaceae – correct

• Brassicaceae (mustard family) includes many metal hyperaccumulators and model phytoextractors such as Brassica juncea, B. napus, and Thlaspi species.​

• A large proportion of known Zn and Ni hyperaccumulators belong to this family, and it is widely cited as the most extensively used plant family in phytoremediation literature, so this option is correct.

3. Malvaceae

• Some Malvaceae members (e.g., Hibiscus, Sida) have demonstrated phytoremediation potential in specific studies, but the family is not the primary, extensively used group across phytoremediation programs.​

4. Annonaceae

• Annonaceae (custard apple family) is better known for medicinal and pharmacological properties than for systematic use in phytoremediation.​

• Only scattered reports exist; it is not considered a major phytoremediation family.

Therefore, among the given options, the plant family Brassicaceae (option 2) has been most extensively used for phytoremediation.