ABSTRACT
Haeckel formalised the concept of using a phylogenetic tree in order to depict the relationships between all the life forms on the planet (see below). The metaphor of the tree seemed to work quite well, and indeed, in Charles Darwin’s magnum opus of 1859
, the only diagram that was used was one depicting a phylogenetic tree. For botanists and zoologists the concept of a phylogenetic tree with large trunks giving rise to smaller branches and then to leaves had so many attractive properties that its position as a central metaphor is almost unshakeable. For microbiologists, however, phylogenetic trees of the prokaryotes have always been problematic; even the definition of prokaryotic and eukaryotic taxa was not satisfactorily resolved until the 1960s
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