Comprehensive plant biology of Viola arsenica Beck

Viola arsenica is a stenoendemic metallophyte from Allchar, an abandoned arsenic (As)-thallium (Tl) mine in North Macedonia. It is one of the three hyperaccumulator Viola species from this area, all belonging to sect. Melanium. This perennial plant inhabits deep soils rich in arsenic and thallium. With foliar concentration of 24,000 μg thallium g-1 d.w., it represents one of the strongest known hyperaccumulators of this toxic element. As a stenoendemic species, it is highly susceptible to habitat disturbance, with global conservation status assessed as critically endangered - CR B2ab(i,iii). Despite recent advances in research, important aspects of the species’ ecology and physiology remain unknown, unclear or poorly understood. Further research is needed to improve our understanding of its eco-physiological adaptations, reproductive biology, vegetation preferences and long-term responses to environmental change.