The study of algae is known as phycology (phyco- comes from the ancient Greek word phūkos, meaning “seaweed”). In the past algae were considered to be lower plants because some forms look like plants. As in plants, the primary photosynthetic pigment in algae is chlorophyll a, and oxygen is produced during photosynthesis. As the variety and complex evolutionary history of algae began to be studied, scientists moved algae out of the Plantae kingdom (in the Eukarya domain) and into the Protista kingdom.