To cite Picante in a publication:

  S.W. Kembel, P.D. Cowan, M.R. Helmus, W.K. Cornwell, H. Morlon, D.D.
  Ackerly, S.P. Blomberg, and C.O. Webb. 2010. Picante: R tools for
  integrating phylogenies and ecology. Bioinformatics 26:1463-1464.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Picante: {R} tools for integrating phylogenies and ecology},
    author = {S.W. Kembel and P.D. Cowan and M.R. Helmus and W.K. Cornwell and H. Morlon and D.D. Ackerly and S.P. Blomberg and C.O. Webb},
    journal = {Bioinformatics},
    volume = {26},
    pages = {1463--1464},
    year = {2010},
  }