Papillio glaucus/canadiensis/glaucus canadiensis

canadensis split from glaucus in 1991.
See HERE for original article that officially split off canadensis

(I'm oversimplifying, but it's close enough) are two kinds of tiger swallowtail: one that was described in 1758 by Linnaeus and given the name of Papilio glaucus, and another described by Rothschild & Jordan in 1906 and given the name of Papilio canadensis.

If you think that they're too closely related to be different species, you name the species that includes both of them by the first name used for either of them, Papilio glaucus. If you think that they're just different enough to be considered as separate subspecies,you add the subspecies name to the end of the species name.

So, what's the subspecies name for the ones like Linnaeus described? By definition, every species contains a subspecies that has the same name as the species. We don't bother with the subspecies name if it's the only subspecies, but it exists. That means that Linnaeus' swallowtails are Papilio glaucus glaucus, while the others are Papilio glaucus canadensis

The confusing part is that the species which includes Linnaeus' swallowtails is always called Papilio glaucus, whether you mean a grouping that doesn't include the canadensis ones or one that does.

To summarize, the choices are:

Separate species
Papilio glaucus (aka Papilio glaucus glaucus, plus any other subspecies)
Papilio canadensis (aka Papilio canadensis canadensis, plus any other subspecies)

Same species,different subspecies
Papilio glaucus glaucus
Papilio glaucus canadensis
(both of which can be called just plain Papilio glaucus if you don't care about subspecies)