To cite rpartOrdinal in publications use:

Kellie J. Archer (2010). rpartOrdinal: An R Package for Deriving a Classification Tree for Predicting an Ordinal Response. Journal of Statistical Software, 34(7), 1-17. URL http://www.jstatsoft.org/v34/i07/.

Corresponding BibTeX entry:

  @Article{,
    title = {{rpartOrdinal}: An {R} Package for Deriving a
      Classification Tree for Predicting an Ordinal Response},
    author = {Kellie J. Archer},
    journal = {Journal of Statistical Software},
    year = {2010},
    volume = {34},
    number = {7},
    pages = {1--17},
    url = {http://www.jstatsoft.org/v34/i07/},
  }