An informal group in
taxonomy
image:Hierarchical clustering diagram.png, 280px, Generalized scheme of taxonomy
Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme o ...
is a
taxonomic rank
In biology, taxonomic rank (which some authors prefer to call nomenclatural rank because ranking is part of nomenclature rather than taxonomy proper, according to some definitions of these terms) is the relative or absolute level of a group of or ...
that is not well defined.
This type of group can be
paraphyletic
Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
or
polyphyletic
A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...
but is kept for ease, pending new systems of classification.
In zoology
Examples can be found in the classification of gastropods:
Opisthobranchia,
Sorbeoconcha,
Hypsogastropoda, and
Ptenoglossa are informal groups nearby the level of the
order
Order, ORDER or Orders may refer to:
* A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
...
.
In
human taxonomy, the informal taxonomic rank of
race is variously considered equivalent or subordinate to the rank of
subspecies
In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...
.
In botany
An
alliance
An alliance is a relationship among people, groups, or sovereign state, states that have joined together for mutual benefit or to achieve some common purpose, whether or not an explicit agreement has been worked out among them. Members of an a ...
is also considered an informal grouping of species,
[A taxonomic revision of Hebe informal group “ Connatae” (Plantaginaceae∗), based on morphology and flavonoid chemistry. Alison V. Kellow, Michael J. Bayly, Kevin A. Mitchell, Kenneth R. Markham and Patrick J. Brownsey, New Zealand Journal of Botany, Volume 41, 2003, Issue 4, pages 613-635, ] genera or tribes to which authors wish to refer, that have at some time provisionally been considered to be closely related.
References
Types of groupings
Gastropod taxonomy
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