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:
  https://f1000research.com/articles/2-191/v2

A BibTeX entry for LaTeX users is

  @Article{,
    title = {taxize - taxonomic search and retrieval in R},
    journal = {F1000Research},
    author = {{Scott Chamberlain} and {Eduard Szocs}},
    year = {2013},
    url = {https://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, Vinh Tran, Maëlle Salmon, Gaopeng Li, and Matthias Grenié.
  (2020) taxize: Taxonomic information from around the web. R package
  version 0.9.98. https://github.com/ropensci/taxize

A BibTeX entry for LaTeX users is

  @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 and Maëlle Salmon and Gaopeng Li and Matthias Grenié},
    year = {2020},
    note = {R package version 0.9.98},
    url = {https://github.com/ropensci/taxize},
  }