Reference:
  Author: K.P. Schliep
  Title: phangorn: phylogenetic analysis in R
  Journal: Bioinformatics 
  Year: 2011
  Volume: 27
  Number: 4
  Pages: 592--593
  DOI: 10.1093/bioinformatics/btq706
  PMID: 21169378
  URL: http://bioinformatics.oxfordjournals.org/content/27/4/592.abstract
