The order Chroococcales includes the most primitive members of the class Cyanophyceae. Almost all the members of the order are fresh water forms which are unicellular and are often organised into regular colonies; but they never show a trichome organisation. They reproduce chiefly by fission or by endospore formation. Heterocysts and hormogonia are absent. The order comprises two families, Chroococcaceae and Entophysalidaceae.
Family Chroococcaceae
Members of the family are unicellular and free-living forms. They occur either singly or in colonies. The individual cells are usually spherical, ovoid, ellipsoidal or cylindrical. Multiplication takes place by fission or sometimes by nannocytes. The common examples of the family are: Anacystis, Aphanocapsa. Chroococcus Gloeocapsa, Microcystis and Synechococcus.
Occurrence
Gloeocapsa (Gr. gloia glue, capsa a box) is a terrestrial or sub-aerial alga generally found on damp soils, wet rocks, banks, etc., as well as in the water reservoirs and lakes. Some species are marine; they occur as a black encrusting film on rocks at the upper limit of the high-tide mark in the littoral zone. Some species of the genus are endophytic, G. alpina constitutes algal component of lichens and occurs in symbiotic association with fungi, whereas G. gelatinosa is found on the hark of Hevea brasiliensis.