When biologists, botanists, etc. use the term "species", they are not using it in a principled way. The distinctions are oftentimes quite arbitrary, I'm very sorry to say.

For what it's worth, there isn't even much agreement on what constitutes a genus or species among professional philosophers of science (i.e. academics who care about giving a principled definition for species/genus), even for those that share many of the same views otherwise (like ur-Platonists, Aristotelians, Thomists, Scotists, etc.).