@book{Willdenow2006,
  author    = {Karl Ludwig Willdenow},
  title     = {Caroli Ludovici Willdenow Florae Berolinensis prodromus secundum systema Linneanum},
  url       = {http://caliban.mpiz-koeln.mpg.de/~stueber/willdenow/flora_berolinensis/index.html},
  year      = {2006},
}