A chemical study of the lichen Ramalina siliquosa complex found in Brittany was conducted. Eight chemotypes were considered and their chemical composition was elucidated for the first time by LC-MS analysis. Ten main compounds were identified: conhypoprotocetraric acid (1), salazinic acid (2), peristictic acid (3), cryptostictic acid (4), protocetraric acid (5), stictic acid (6), norstictic acid (7), hypoprotocetraric acid (8), 4-O-demethylbarbatic acid (9), (+)-usnic acid (10) and 22 minor compounds were reported. The MS/MS fragmentation patterns of each compound of R. siliquosa complex were determined and proposed.