@Rogue_Koala @Fullycaffeinated Not all plants are vascular.

Plants are the dominate photosynthesizer on land, so we are the most familiar with them. They all belong to the same group of organisms, which evolved from green algae, and is likely closely related to red algae.

So plants are one group of organisms by relatedness. Algae is a larger category of organisms that encompasses all photosynthetic organisms, no matter where they are on the tree of life.

"Officially" (because the morons run the world) plants are not algae. But this is just an arbitrary rule, that past a certain point on that branch of the tree of life, we don't call them algae anymore because they are too "complex"