To cite the R package 'clustergas' in publications use:

Castellanos-Garzon, J. A., Diaz, F.(2012). clustergas: A hierarchical clustering method based on genetic algorithms. Department of Computer Science, University of Valladolid, Spain. R package version 1.0.

Corresponding BibTeX entry:

  @Manual{,
    title = {clustergas: A hierarchical clustering method based on
      genetic algorithms},
    author = {Jose A. Castellanos-Garzon and Fernando Diaz},
    organization = {Department of Computer Science, University of
      Valladolid},
    address = {Valladolid, Spain},
    year = {2012},
    note = {R package version 1.0},
  }