To cite evtree in publications use:

Thomas Grubinger, Achim Zeileis, Karl-Peter Pfeiffer (2014). evtree: Evolutionary Learning of Globally Optimal Classification and Regression Trees in R. Journal of Statistical Software, 61(1), 1-29. URL http://www.jstatsoft.org/v61/i01/.

Corresponding BibTeX entry:

  @Article{,
    title = {{evtree}: Evolutionary Learning of Globally Optimal
      Classification and Regression Trees in {R}},
    author = {Thomas Grubinger and Achim Zeileis and Karl-Peter
      Pfeiffer},
    journal = {Journal of Statistical Software},
    year = {2014},
    volume = {61},
    number = {1},
    pages = {1--29},
    url = {http://www.jstatsoft.org/v61/i01/},
  }