Isoasparagine was isolated for the first time as a natural product from Chara corallina. It was characterized by elementary analysis, the optical rotation value and the 1 H NMR spectrum, as well as analyses of the hydrolysis products. Identification was confirmed by comparison with a synthetic sample. Seeds and green parts of Plantago species have been examined for a supposed content of glucosinolates. Sensitive methods of quantitative glucosinolate analysis have been used but no glucosinolates could be detected. The significance of this investigation is briefly discussed in relation to chemotaxonomy and previously reported occurrence of isothiocyanates in extracts from Plantago species.