To cite rotl in publications use:

  Michonneau, F., Brown, J. W. and Winter, D. J. (2016), rotl: an R
  package to interact with the Open Tree of Life data.  Methods in
  Ecology and Evolution. 7(12):1476-1481. doi:10.1111/2041-210X.12593

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{rotl}: an R package to interact with the Open Tree of Life data},
    author = {Francois Michonneau and Joseph W. Brown and David J. Winter},
    journal = {Methods in Ecology and Evolution},
    year = {2016},
    volume = {7},
    number = {12},
    pages = {1476-1481},
    doi = {10.1111/2041-210X.12593},
  }

You should also cite the source data from the Open Tree of Life

  OpenTree et al. Open Tree of Life Synthetic Tree.
  doi:0.5281/zenodo.39377411

A BibTeX entry for LaTeX users is

  @Misc{,
    title = {Open Tree of Life Synthetic Tree},
    author = {{OpenTreeOfLife} and Benjamin Redelings and Luna Luisa Sanchez Reyes and Karen A. Cranston and Jim Allman and Mark T. Holder and Emily Jane McTavish},
    year = {2019},
    version = {12.3},
    publisher = {Zenodo},
    doi = {10.5281/zenodo.3937741},
    url = {https://doi.org/10.5281/zenodo.3937741},
  }