Ranks and nomenclatureTaxonomyTaxonomy is the the ordering of plant species in the form of a tree. Species belong to families, families belong to order, orders to classes and so on. Each group has a rank in the tree.
Family is a rank and order is a rank higher. A big problem to ascertain how many steps exist in the tree. In botany this is difficult as there is no criterion to ascertain a rank, to establish how high it is in a tree. A group that is treated as a family in one taxonomy is treated as a subfamily in another taxonomy. That is way sometimes names and ranks vary considerably in the literature. The amount of ranks has been increased greatly and sometimes enormously, often based on phylogenetic analyses. In Wikispecies for instance, the order
Anura has 21 ranks above it. This doesn't make taxonomy more simple. On the contrary, it makes is very complex. Most ranks don't have names anymore, they are only described as clade, a group. Above that there is not just only a phylum, but also a superphylum, subphylum, and infraphylum.
The problem can be encountered frequently in expressions of botanist like “The nomenclature and classification of plants with microphylls varies substantially among authors”.
NomenclatureThe nomenclature, the naming of a group, is an expression of the taxonomy.
Groups of the same rank are given the same ending. The rank of the group is then evident from the name.
In botany families have names ending in "aceae". Orders have a name ending in "ales". Subclasses mostly have a name ending in "idae". For classes this is less straightforward, they sometimes end in "opsida", sometimes in "anae", or even in "phyta". The ending "phyta" though is generally used for divisions. The confusion becomes evident for the class Lycopodiopsida. They are known as Lycopsids, Lycopods, or Lycophytes. It also arises from the confusion of the rank of the group: is it a class or division, or something in between, or some other rank?
Plant theoryIn the
Plant theory the ranks are limited to 7. And each rank has a specific quality. The ranks are species, family, order, subclass, class, division and kingdom.
In the
Plant theory the ending are generally the same as in botany. The main exclusion is for classes, which have the ending of "anae". The ending "phyta" was excluded because that ending was also used for dieisions. The ending "opsida" was put aside because several genera have such and ending and because it is quite awkward.
In the
Plant theory ranks and name endings are thus as follows:
Family: aceae.
Order: ales.
Subclass: idae.
Class: anae.
Division: phyta.