To cite package ‘ggpp’ in publications use:

  Aphalo P (2024). _ggpp: Grammar Extensions to 'ggplot2'_. R package
  version 0.5.8-1, <https://CRAN.R-project.org/package=ggpp>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {ggpp: Grammar Extensions to 'ggplot2'},
    author = {Pedro J. Aphalo},
    year = {2024},
    note = {R package version 0.5.8-1},
    url = {https://CRAN.R-project.org/package=ggpp},
  }