To cite taxize in publications use at least the first, if not both:

Scott Chamberlain and Eduard Szocs (2013). taxize - taxonomic search and retrieval in R. F1000Research, 2:191. URL: http://f1000research.com/articles/2-191/v2.

Scott Chamberlain, Eduard Szoecs, Zachary Foster, Zebulun Arendsee, Carl Boettiger, Karthik Ram, Ignasi Bartomeus, John Baumgartner, James O'Donnell, Jari Oksanen, Bastian Greshake Tzovaras, Philippe Marchand, and Vinh Tran. (2018) taxize: Taxonomic information from around the web. R package version 0.9.3. https://github.com/ropensci/taxize

Corresponding BibTeX entries:

  @Article{,
    title = {taxize - taxonomic search and retrieval in R},
    journal = {F1000Research},
    author = {{Scott Chamberlain} and {Eduard Szocs}},
    year = {2013},
    url = {http://f1000research.com/articles/2-191/v2},
  }
  @Manual{,
    title = {taxize: Taxonomic information from around the web},
    author = {Scott Chamberlain and Eduard Szoecs and Zachary Foster
      and Zebulun Arendsee and Carl Boettiger and Karthik Ram and
      Ignasi Bartomeus and John Baumgartner and James O'Donnell and
      Jari Oksanen and Bastian Greshake Tzovaras and Philippe Marchand
      and Vinh Tran},
    year = {2018},
    note = {R package version 0.9.3},
    url = {https://github.com/ropensci/taxize},
  }