Marine Algae and Seaweeds; Archaeplastida plus

When considered as a group, the marine algae and associated photosynthesising lifeforms are essential to the function of the whole undersea ecosystem.
Big thanks to marine biologist Stefano Draisma from the Prince of Songkla University who has put us right on most of our somewhat shaky identification. And thank you for diving with us, sir!
Needless to say, a wide variety of marine algae can be spotted around and about most of the Koh Phangan dive sites.

Not all algae are plants! Many of what we would call seaweeds are actually in the phylum Heterokonta... (3 Galleries)

Most of them use phycobiliproteins as accessory pigments, which give them their red colour!

These all come under the category of Viridiplantae, yet only the sea grass is a true plant.

Placed here for convenience although they actually belong to the domain of the bacteria. They are prokaryotic rather then eukaryotic organisms.