What do the letters BXP and second taxonomic notation mean on this record?
The letters B.X.P. are the initials of the authors. There may be a typo here, as I think it should actually be B.S.P. (for Britton, Sterns, & Poggenburg).
I'm not sure about the other taxonomic notation. It looks there's another typo, though, because it should actually be "G. chapmanianus", which is a closely related species of skeletongrass. Perhaps the notation means the two species can be easily confused (educated guess, I don't exactly know).