What the heck is seaweed anyway?

Sometimes we take our phycological education for granted and forget that algal terminology can be a bit confusing. Let’s review some basic concepts to ensure that we are all on the same page when thinking about seaweed.

Alga = singular

Algae = plural

Algaes = not a real word

Microalgae = single cell algae species

Macroalgae = multi-cellular algae species = seaweed

3 branches of algae = red (Rhodophyta), green (Chlorophyta), brown (Ochrophyta)

Kelp = a branch of brown seaweeds (Laminariales)

Plant = Photosynthetic thing on land

A very brief overview of the evolution of photosynthetic organisms.

In the beginning there was a bacterium that learned a neat trick. This bacterium contained pigments that allowed it to capture sunlight and convert it into energy via photosynthesis. The bacterium was engulfed and incorporated by another single celled organism (a eukaryote), this event is called primary endosymbiosis. Its a partnership between the two cells (bacterium and eukaryote) similar to the photosynthetic algae that like inside corals. Through this process red, and then later green, algae came into existence. After this primary endosymbiotic union, secondary and even tertiary endosymbioses occurred - algal cells themselves getting engulfed and incorporated to give rise to other algal groups including macroalgae, browns, and terrestrial plants. If you want to dive into the specifics of how scientists discovered this, here is a good paper outlining how the genetic code of algae lead to the discovery.


It may seem a little complicated, and in fact it is, its very complicated. But it is super cool and for this reason we don’t like algae being called plants; it’s like calling “fish” … “humans.” On a more humorous note, we do encourage people to call plants, “land-adapted algae”. Again, check out algaebase.org to review all of this and see where your favorite seaweed fits in.