A robust phylogenetic tree comes with a fixed branching order of leaves. One looks at the leaf names and their taxonomic lineage and tries to map the latter to the branches. To this end we added the following paragraphs in the “Material and Method” section. “There are two aspects of a phylogenetic tree: the branching order (topology) and the branch lengths. Branching order is related to classification and branch length to evolution time. Calibration of branch lengths is always associated with the assumption that mutation rate remains more or less a constant across all species represented in a tree, an assumption that cannot hold true in a large-scale phylogenetic study like the present one. Therefore, branching order in trees is of primary concern, whereas calibration of branch lengths makes less sense. Accordingly, all figures in this paper only show the branching scheme without indication of branch lengths and bootstrap values.” “Branching order in a tree by itself does not bring about taxonomic ranks, e,g, class or order.
Taxonomists have traditionally circumscribed the high taxa (specially orders and classes) with great subjectivity, i.e., without well accepted criteria. In terms of phylogenetic trees one premise has always been clear, a taxon must be monophyletic. This principle has been used in the present work to reconsider the status of some high taxa. However, authors do not explain objective criteria to properly interpret the rank of the clades, which impedes making a profound evaluation of the archaeal classification. Therefore, although authors have strong tools and dataset, they just achieved a small revision of the high taxa which is, indeed, quite biased by the underlying 16S guidelines.