To cite package 'plotrix' in publications use:

Lemon, J. (2006) Plotrix: a package in the red light district of R. R-News, 6(4): 8-12.

Corresponding BibTeX entry:

  @Article{,
    year = {2006},
    title = {Plotrix: a package in the red light district of R},
    journal = {R-News},
    volume = {6},
    number = {4},
    pages = {8-12},
    author = {Lemon J},
  }