Seaweeds (or macroalgae) are aquatic photosynthetic organisms belonging to the domain Eukarya and to kingdoms Plantae (green and red algae) and Chromista (brown algae). Although classification systems have varied greatly over time and according to the authors, the following are generally agreed:

The green algae are included in the phylum Chlorophyta and their pigmentation is identical to that of terrestrial plants (chlorophyll a, b and carotenoids).

The red algae belong to the phylum Rhodophyta and their photosynthetic pigments are chlorophyll a, phycobilins (R-phycocyanin and R-phycoerythrin) and carotenoids, mostly β-carotene, lutein and zeaxanthin.

The brown algae are included in the phylum Ochrophyta (or Heterokontophyta), class Phaeophyceae, and their pigments include chlorophylls a, c and carotenoids, dominated by fucoxanthin (Pereira 2009, Pereira 2018).