The common character between Gracilaria, Laminaria, Spirogyra and Nostoc is:
The common character between Gracilaria, Laminaria, Spirogyra and Nostoc is presence of pigment chlorophyll a. Gracilaria has chlorophyll a and d, Laminaria has Chlorophyll a and c, Spirogyra has chlorophyll a and b. Nostoc has the presence of chlorophyll a.