Abstract
The taxonomical survey of the hiperhaline lagoon of Araruama showed that five taxa of Ulvales and Cladophorales presented great morfological variations. Descriptions, morphological variations, comments and illustrations of Enteromorpha flexuosa subsp. flexuosa, Ulva lactuca, U. rigida, Cladophora vagabunda and Rhizoclonium tortuosum are given. The abiotic factors that may cause these variations are discussed.