Fig 2. Changes in frond biomass of the As-hyperaccumulator ferns P. cretica var. Albo-lineata and P. cretica var. Parkerii and the As-non-hyperaccumulator fern P. straminea after 23 weeks of exposure to As.

Values are mean ± standard error (SE). Data with the same letter are not significantly different. Different letters indicate significant differences (p < 0.05) among variants of each fern (lower-case letters) and among the individual ferns of each variant (upper-case letters) according to the Kruskal-Wallis test. Treatment abbreviations: control– 0 mg As·kg^-1 soil; As1–20 mg As·kg^-1 soil; As2–100 mg As·kg^-1 soil. The background soil As content is 16 mg As·kg^-1 soil. The difference between control and individual As treatments is the spiked As dose plus the 20% As extraction efficiency.