Diverse and divergent group of unicellular,colonial, and filamentous oxygenic and photosynthetic bacteria. Filamentous types simple or with falseor true branches (sometimes with both); some filamentous types multiseriate, forming more complex mulicellular thalli. Cell breadth or diamerter randes form less then 0.5 ไมโครเมตร to over 100 ไมโครเมตร. Stain Gram negative; outer membrane present; peptidoglycan layer 2-200 nm thick (T.E.M.); most filamentous forms have minutepores between cells (miceoplasmodesmata)(T.E.M.).