Sagan 4's seed-bearing "shrooms" would probably make botanists and mycologists alike cry, for a myriad of reasons. A real mushroom evolving to produce pollen is absurd--their methods of genetic exchange simply don't work that way! And for the poor botanist, what do you mean the pollen is a modified "seed", which itself is in reality technically an achene? And their ancestors had a gametophyte stage that's just gone now??
In reality, plants can be absurd aliens that work completely different from everything you know, too.