To cite glmertree in publications use:

MArjolein Fokkema, Niels Smits, Achim Zeileis, Torsten Hothorn, Henk Kelderman (2018). partykit: A Modular Toolkit for Recursive Partytioning in R. Behavior Research Methods 50(5), 2016-2034. URL http://link.springer.com/article/10.3758/s13428-017-0971-x

Corresponding BibTeX entry:

  @Article{,
    title = {Detecting Treatment-Subgroup Interactions in clustered
      Data With Generalized Linear Mixed-Effects Model Trees},
    author = {Marjolein Fokkema and Niels Smits and Achim Zeileis and
      Torsten Hothorn and Henk Kelderman},
    journal = {Behavior Research Methods},
    year = {2018},
    volume = {50},
    issue = {5},
    pages = {2016-2034},
    url = {http://link.springer.com/article/10.3758/s13428-017-0971-x},
  }