Phytoremediation and ethnomedicinal potential of Buddleja, Eremophila, Scrophularia, and Verbascum genera belonging to the Scrophulariaceae family: a review

A number of species have developed detoxification strategies that allow them to accumulate high amounts of heavy metals in their tissues and grow despite a high heavy metal (HM) concentration in soils. Thus, they are considered hyperaccumulator or accumulator species, attractive for phytoremediation purposes. Families reported to contain a high number of hyperaccumulator species are Asteraceae, Euphorbiaceae, Rubiaceae, Fabaceae, Scrophulariaceae, Myrtaceae, Proteaceae, Caryophylaceae, and Tiliaceae. Indeed, the family Scrophulariaceae has a large extension, with Buddleja, Eremophila, Scrophularia, and Verbascum being some of the best-known genera containing species used for medicinal purposes. This review focuses on identifying the species used in folk medicine that belong to these four genera and can accumulate high concentrations of heavy metals (HMs). Additionally, the human health risks related to the consumption of HM hyperaccumulator species are discussed, as well as the feasibility of plant tissue culture to provide safe vegetal material for medicinal uses or to estimate the intrinsic potential of species for phytoremediation purposes. The following species have demonstrated the ability to accumulate HMs and grow in mine or HM-polluted soils, as well as use in traditional medicine: Buddleja asiatica, B. cordata, B. davidii, B. lindleyana, B. macrostachya, B. paniculata, B. scordioides, Eremophila latrobei, Scrophularia canina subsp. bicolor, S. ningpoensis, S. striata, Verbascum bombyciferum, V. olympicum, V. phrygium, and V. thapsus. In some of these species, antioxidant machinery has been proven to participate as a defense strategy against exposure to high HM concentrations. Consuming plants that accumulate high amounts of HMs has been described as a potential risk to human health. Plant tissue culture has also been established in a few of these species, whether to propagate or use them as a bioactive phytochemical source. Promoting safety and quality control related to the HM concentrations in the tissues of these plants used by populations for curative purposes is necessary. Further research must be carried out on several species for phytoremediation purposes.

Graphical abstract