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 Szocs, Carl Boettiger, Karthik Ram, Ignasi Bartomeus, John Baumgartner, Zachary Foster, and James O'Donnell (2016) taxize: Taxonomic information from around the web. R package version 0.7.4. 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 Szocs and Carl Boettiger and
      Karthik Ram and Ignasi Bartomeus and John Baumgartner and Zachary
      Foster and James O'Donnell},
    year = {2016},
    note = {R package version 0.7.4},
    url = {https://github.com/ropensci/taxize},
  }