Abstract
The carotenoid pigments of 50 species of 9 siphonean orders were investigated. The algae of all orders contain the principal carotenoids known from other green algae: α- and β-carotene, lutein, lutein epoxide, violaxanthin, and neoxanthin. Additionally, in some Siphonodadales siphonaxanthin is present, in the Derbesiales, Codiales, and Caulerpales both siphonaxanthin and its ester siphonein are present, whereas in the Dichotomosiphonales only the ester siphonein can be found. The chemotaxonomical value of siphonaxanthin and siphonein is discussed.