To cite ips in a publication use:

Heibl C (2008 onwards). “IPS: R language interfaces to diverse phylogenetic software packages. http://www.christophheibl.de/Rpackages.html.”

Corresponding BibTeX entry:

  @Misc{Heibl2008,
    title = {IPS: R language interfaces to diverse phylogenetic
      software packages. http://www.christophheibl.de/Rpackages.html},
    author = {Christoph Heibl},
    year = {2008 onwards},
  }