Dinobryon, a colonial alga from the Chrysophyceae group
A seaweed (
Laurencia). Much smaller algae are attached to the structure extending upwards in the lower right quarter
Phytoplankton bloom in the south Atlantic off Argentina
Algae (singular: alga, plural: algae) are plant-like living things. They make food from sunlight by photosynthesis. The study of algae is called phycology or algology.
The term covers different groups, and they are not all closely related. They are a polyphyletic group. The term lumps together different kinds of organisms. They are very ancient, and existed long before other types of plants. They date back to the Mesoproterozoic, over a thousand million years ago. They are not quite the first type of life, because they all seem to use plastids which originate in cyanobacteria.