A cell wall material present only in blue green algae and bacteria is

There are many similarities between cyanobacterium and bacterium. They both posses saparophytic mode of life. They both lack true cell organelles. They both posses nucleoid instead of true nucleus. In both bacteria and blue green algae, the cell wall is made up of muramic acid and diaminopimelic acid. Thus, the correct answer is 'Muramic acid.'