What characteristic is common to both unicellular and multicellular algae?

Euglenoids, dinoflagellates, and usually Diatoms are unicellular while brown algae, red algae and green algae may be multicellular. Photosynthetic pigments are found in all algae like chlrophyll a and yellow or orange carotenoids. Also, almost all algae is aquatic. Also, all algae are eukaryotes and the sex organs are unicellular in all algae.