Environmental contamination by heavy metals is a growing concern due to their adverse impacts on plant health and ecological stability. In this study, the potential of Ramalina farinacea (L.) Ach. lichen extract to mitigate the toxic effects of nickel chloride (NiCl₂) on Allium cepa L. was investigated. The bulbs were exposed to various treatment groups, and a series of physiological, cytogenetic, biochemical, and anatomical analyses were performed. Throughout the experimental period, the control group was treated with tap water, while the treatment groups were treated with 0.5 g L−1 R. farinacea extract, 1.0 g L−1 R. farinacea extract, 1 mg L−1 NiCl2, 1 mg L−1 NiCl2 + 0.5 g L−1 R. farinacea extract, and 1 mg L−1 NiCl2 + 1.0 g L−1 R. farinacea extract, respectively. NiCl₂ exposure significantly impaired root development, disrupted mitotic activity, elevated oxidative stress markers, and caused DNA and chromosomal damage. Micronucleus (MN), sticky chromosome, vagrant chromosome, fragment, unequal chromatin distribution, bridge, vacuolated nucleus, and irregular mitosis were among the chromosomal aberrations (CAs) brought on by NiCl₂. However, co-treatment with R. farinacea extract effectively alleviated these adverse effects in a dose-dependent manner. The lichen extract restored mitotic index values, reduced CAs and MN formation, decreased malondialdehyde and proline accumulation, and helped preserve chlorophyll content and meristematic tissue integrity. LC–MS/MS analysis confirmed the presence of phenolic compounds with known antioxidant and metal-chelating activity, such as p-coumaric acid, ferulic acid, gentisic acid, vanillin, taxifolin, 4-hydroxybenzoic acid, and syringic acid. These findings highlight the protective role of R. farinacea extract against Ni-induced phytotoxicity and genotoxicity in A. cepa, suggesting its promising potential as a natural bioprotective agent for environmental and agricultural applications. Keywords: Allium cepa, Cytogenotoxicity, Heavy metal, Lichen extract, Phenolic, Ramalina farinacea.