To cite treeio in publications use:

  Guangchuang Yu. (2022). Data Integration, Manipulation and
  Visualization of Phylogenetic Trees (1st edition). Chapman and
  Hall/CRC.

A BibTeX entry for LaTeX users is

  @Book{,
    title = {Data Integration, Manipulation and Visualization of Phylogenetic Treess},
    author = {Guangchuang Yu},
    publisher = {Chapman and Hall/{CRC}},
    year = {2022},
    edition = {1st edition},
    url = {https://www.amazon.com/Integration-Manipulation-Visualization-Phylogenetic-Computational-ebook/dp/B0B5NLZR1Z/},
  }

  LG Wang, TTY Lam, S Xu, Z Dai, L Zhou, T Feng, P Guo, CW Dunn, BR
  Jones, T Bradley, H Zhu, Y Guan, Y Jiang, G Yu. treeio: an R package
  for phylogenetic tree input and output with richly annotated and
  associated data. Molecular Biology and Evolution 2020, 37(2):599-603.
  doi: 10.1093/molbev/msz240

A BibTeX entry for LaTeX users is

  @Article{,
    title = {treeio: an R package for phylogenetic tree input and output with richly annotated and associated data.},
    author = {Li-Gen Wang and Tommy Tsan-Yuk Lam and Shuangbin Xu and Zehan Dai and Lang Zhou and Tingze Feng and Pingfan Guo and Casey W. Dunn and Bradley R. Jones and Tyler Bradley and Huachen Zhu and Yi Guan and Yong Jiang and Guangchuang Yu},
    year = {2020},
    journal = {Molecular Biology and Evolution},
    volume = {37},
    issue = {2},
    pages = {599-603},
    doi = {10.1093/molbev/msz240},
  }