Repetition of "Clade" in a taxonomic tree

Question

Animals and plants are somtimes classified (organized) into a taxonomic tree data structure. The term "tree data-structure" comes from the fields of computer science and software development.

On Wikipedia this taxonomy sometimes has more than one field named "Clade". How is it possible for more than one tier of the taxonmic tree of life to be named "Clade"?

Kingdom:
Clade:
Clade:
Clade:
Clade:
Order:
Family:
Genus:
Species:

Why would "Clade" be repeated more than once?

Are the instances of the text "Clade" supposed to be "phylum", "class", and "Order"?

Answer 1

Wikipedia employs multiple taxonomy databases. The page gives an idea of conflicts of consensus and for official species classification. The ball python has 10 levels of classification and the rose has 11. One is a plant, the other is a reptile. Biology didn't give them tidy class and phylum ranks.

I don’t think we need to get rid of [taxonomic ranks]

[...]

What we need to abandon is the unwarranted connotations that higher-level taxa are comparable. Because they aren’t. They are abstractions. They are information storage boxes. That’s all they are.

_{Ronald Jenner, a phylogeneticist}

Linnaeus invented ranks (uniform levels of nesting that he applied across groups of organisms) to organize his understanding of diversity. The original ranks designated by Linnaeus were kingdom, class, order, genus and species, and others, including the phylum, have been added since. As phylogenies improve, some have called for the abandonment of ranks to avoid implying that different clades given the same rank are comparable.

There have never been clear objective criteria for designating a clade as a phylum. There is, for example, no known property that is shared by all echinoderms or all molluscs, both of which have been designated as phyla, and that would distinguish these clades from more or less inclusive clades that aren’t phyla, such as deuterostomes or bivalves. This has provoked considerable discussion about whether the categorization into phyla says more about the way humans perceive animal diversity or the biological processes that generated this diversity

_{Ref.: Andreas Hejnol, Casey W. Dunn, Animal Evolution: Are Phyla Real?, Current Biology, Volume 26, Issue 10, 2016, DOI: 10.1016/j.cub.2016.03.058}

UK and USA textbooks don't have the same number of kingdoms, one has 5 and the other has 6, other theories have 32.

Super and sub ranks also exist, like superfamily and subphylum.

Taxonomy is most often a spectrum of variety with unclear or overlapping divisions, like a rainbow, and words are attempts to put labels onto the divisions of the spectrum.

Different cultures and regions employ words that segment the spectrum of knowledge into different compartments, artificially. That is especially mired by the complexity of taxonomy grouping.

For taxonomic hierarchy, there’s some sense in which the phylum and the species both have rigorous currency, however the intermediary levels are a kind of construct.

_{Ref.: https://www.quantamagazine.org/phyla-and-other-flawed-taxonomic-categories-vex-biologists-20190624/}

Answer 2

The idea of a clade and taxa (phylumn, class, order, etc.) are two different, but sometimes overlapping approaches to the classification of organisms. In short, a clade is any group of organisms that contain a common ancestor and all of its descendants, and is sometimes said as monophyletic. On the other hand, a taxon is a group of organisms that fits in to the taxonomical ranking system. Due to the limitation of technology and molecular evidence in the past, not all taxa reflect the evolutionary relationship.

On the wikipedia page, many clade are included as a result that an organisms can fit in groups within group. Take the clade Angiosperms and Monocot, an angiosperms is any flowering plants and this clade contain another clade within. That is, the Monocot, which are flowering plants with a single cotyledon (embryonic leaf) in the seed. Keep in mind the Angiosperms and Monocots are clade, meaning that is a natural group in the sense that it reflects the evolutionary history of the organisms within the group.

So, to answer your question, a clade does not always represent, or equal to a taxon. The purpose of including the clades is to provide finer details with regard to the evolutionary history and phylogenetic relationship to a given organism.

Suggested readings and relevant question:

1. What is the difference between these terms: clade, monophyletic group and taxon?
2. Monophyly (wikipedia)
3. Clade (wikipedia)