Algae of the genus Cystoseira make up most of the benthic flora in the Adriatic Sea, and as they prefer clean habitats, they are considered as indicator species. Algae forests of the Cystoseira genus are extremely important for marine ecosystems because they represent place for hiding, breeding grounds and feeding grounds for many species. The paper emphasizes the risks and endangered categories of the Adriatic species of the genus Cystoseira. Also, the definitions of benthos and phytobenthos are presented and the basic characteristics of the species Cystoseira spicata, Cystoseira barbata var. tophuloidea, Cystoseira compressa, Cystoseira crinitophylla, Cystoseira foeniculacea, Cystoseira humilis, Cystoseira humilis var. myriophylloides and Cystoseira pelagosae, which are on the Croatian red list of seaweeds and flower plants, are described. Available data on the distribution of algae in the Adriatic Sea, regardless the degree of endangerment, are incomplete as the mapping of the Adriatic marine flora, which should provide precise data on the distribution and consequently the level of threat of the species, has not been finalized yet.