Seaweed is actually a plant-like protist, which are also known as algae. The green color is due to what pigment? Algae, like plants, obtain their energy through photosynthesis.

Why are seaweed protists?

Algae are part of the 'Kingdom Protista', which means that they are neither plants nor animals. Seaweeds are not true plants because they lack a vascular system (an internal transport system for fluids and nutrients), roots, stems, leaves, and enclosed reproductive structures like flowers.

What is a seaweed classified as?

Seaweeds are classified into brown algae (Phaeophyta), red algae (Rhodophyta), and green algae (Chlorophyta). Note that in reality the term algae is mainly used for convenience, rather than taxonomic purposes, as there appears little relationship between the various phyla.