The first investigations carried out on the lipophilic content of samples of the brown alga, Cystoseira nodicaulis, collected along the Atlantic coasts of France led to the isolation of a single monocyclic meroditerpene previously identified in Cystoseira elegans. This finding supplements the chemical data available about the Sargassaceae family and opens the way to further discussions about taxonomy through comparisons with phylogenetic studies. Cyclized meroditerpenes are a typical feature of the clade that includes C. nodicaulis and its allied species C. elegans and Cystoseira baccata.