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.

A BibTeX entry for LaTeX users is

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