Algae

Algae was a kind of plant which thrived in water. The seas of Mal Oreille were yellow due to the peculiar kind of algae that lived in them. (PROSE: Biology Lesson on Mal Oreille)

Algae was also edible, and the Emojibots cultivated it for the colonists on a human colony planet. This reminded the Twelfth Doctor of the algae emperor who had a crush on him. (TV: Smile)