It was only in 1969 (nice) that fungi officially became its own separate kingdom.
The definition of planet is completely subjective, whereas the definition of mushroom is based on science and evolution.
Planet used to mean wandering star, referring to ‘stars’ that didn’t stay in one place but moved around with the days, months, years, or centuries. Obviously not a useful definition these days, I consider a planet a rocky body big enough that it’s gravity makes it almost perfectly round.