Pokémon with only one gender
There are even Pokémon that possess only one gender. Here, you don’t have to worry about how they look and which specimen you are dealing with. The first known examples are Nidorina and Nidorino, which evolve into Nidoqueen and Nidoking respectively, according to their gender.
For many Pokémon, this makes sense: Miltank is always female because it has a udder. The male counterpart is Tauros. Honweisel is a queen bee, so it is only logical that this Pokémon exists only in female form.
