Seaweed is a term that denotes the green, red, and brown algae which grow in the ocean. If we follow their lineages, we see that out of the 8 eukaryotic supergroups, green and red algae belong in Archaeplastida and brown algae in Stramenopiles. Green algae have evolved into land plants. Red algae grew quietly in the ocean for one billion years, and brown algae came to play the leading role in marine and coastal ecosystems in the last hundred million years. Seaweed sustains the global environment as a blue carbon producer.