My understanding of the issues at hand tells me that your first and second groups are not valid for scach, while your third group might be subject to a machlokes.
- Algae and the like are not גדולי קרקע, as they do not grow in the ground.
- Mushrooms (a form of fungus), even when they grow on the ground, are not considered to be גדולי קרקע with regard to brachos, because we make the bracha of shehakol rather than ha'adamah, because they do not derive nourishment from the ground.
- Hydroponics might depend if you make the bracha of ha'adamah on them or not -- if you do, then they are גדולי קרקע; if you make a shehakol, then they might1 not be גדולי קרקע.
This is my own, unsourced understanding of the issues at hand. If you disagree, please feel free to leave constructive comments to let me know where I went wrong.
1 The reason that I wrote "might not be," is because a case might be made that these plants are, by their very essence, גדולי קרקע and not subject to change based on where this particular specimen grew. I can't say for certain whether or not that is true, but my (unbased) feeling is that it would depend on where this particular specimen grew.
In retrospect, this may have been the intent of the question :P