Parasitism has proven to be an efficient way for organisms to survive. Parasitic plants rely on their host at least to some extent for their photosynthetic activities, and therefore their survival. Parasitism has evolved independently at least 12 times across the angiosperms tree of life with around 1 % of plant species showing at least partial parasitism. The sandalwood order Santalales encompasses the largest number of parasitic species, including the iconic mistletoe Viscum sp. Mitochondria are essential organelles for plant functions, involved in key cellular processes and metabolic pathways. Their primary role is the generation of ATP, but they are also involved in e.g. programmed cell death and stress response. Compared to animals, plants exhibit complex and larger mitochondrial genomes ranging from 191 kb to 11.3 mb. This is due to the presence of large introns, repetitive elements and horizontal-gene transfers. Recent work has suggested that plant mitogenomes have a dynamic non-circular structure (linear, branching), with a combination of physical forms caused by sequence recombination (Kozic et al. 2019). They comprise the same respiratory complexes I-V as in animals, with additional subunits in complexes I and II. They also include genes encoding for the maturase-related protein matR, for protein of the small and large subunits of the ribosomes (rps and rpl), and genes involved in the cytochrome C biogeneiss pathway. The respiratory complexes I, III, IV and V are considered core genes, present in most sequenced autotrophic and parasitic plants (Fan 2016). Due to the crucial role of mitogenomes in plant functions, their structure is not expected to be impacted by parasitism. However, recent findings have challenged this view, suggesting that some genes of the mitogenome might be expandable, particularly those involved in the respiratory pathway. Some Visaceae species have lost an exceptional number of mitochondrial genes including all complex I genes of the respiratory chain (Petersen et al. 2015, Skippington 2015, Zervas et al. 2019). They also exhibit very fast molecular evolution rates (Zervas et al. 2019). To understand how the mitochondrial genome is affected in parasitic plants, it is important to expand the sampling to all Santalales. This project investigates how the mitogenome architecture, especially the respiratory pathway, has evolved in Santalales by characterizing gene loss through comparative genomics and molecular evolutionary rates of mitochondrial genomes. To finish, we investigate whether possible gene loss in the respiratory chain is correlated to different levels of parasitism, or whether it is clade-specific, across all Santalales.