The natural floridoside (2-O-alpha-d-galactopyranosylglycerol) was isolated from Dilsea carnosa, and its structure has been determined by single-crystal X-ray diffraction analysis. The solved structure is in agreement with the previously solved crystal structure of floridoside [Simon-Colin, C.; Michaud, F.; Léger, J.-M.; Deslandes E. Carbohydr. Res.2003, 338, 2413-2416] and demonstrates for the first time the presence of floridoside in the red algae Dilsea carnosa.