Adding green algae to the database opens an enormous, and rather absurd, can of worms.
There are tens of thousands of species of green algae, most of which can't be distinguished from each other by anyone but a few specialists in the field. Or, maybe not, no one is really sure how many species there might be or how to coherently categorize them. No one is sure green algae are even a "thing". They may be a collection of groups of unrelated organisms that just resemble each other after 3+ billion years of convergent evolution. We may have just lumped them together because it was convenient and we don't even know what we don't know about them.
Once you add green algae, there's no justification for not adding lichens. Again, that's 10's of thousands new entries for an even messier and more poorly understood taxon that can even less accurately be called "plants".
Once you've added lichens, there's no reason, from a taxonomic standpoint, to keep out fungi which can't even vaguely be considered plants and are also poorly understood, although better than algae and lichens.
Many plant biologists don't currently consider green algae to be members of the Kingdom Plantae, although there's an ongoing (seemingly never ending) debate about that.
Lastly, what would we gain by opening this giant and very confusing can of worms? Most likely, vast numbers of additional blank entries and a few pictures of (probably misidentified) pond scum. With no real upside that I can see?
