THE ALGAL MICROFLORA ON CALCAREOUS WALLS OF FRIULI - VENEZIA GIULIA (NE - ITALY). The algal biotopes are mostly populated by Cyanophytes. The most abundant Algae are Gloeocapsa and Scytonema. Microphytic communities are described phytosociologically. The algal vegetation is similar to Scytonemo - Gloeocapsetum described by Golubić (1967). The lithophytic vegetation of three localities of different microecology is compared. Some difference with regard to the relative abundance of coccoid and filamentous species is detected.