Cairina is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of duck

Duck

Duck is the common name for a large number of species in the Anatidae family of birds, which also includes swans and geese. The ducks are divided among several subfamilies in the Anatidae family; they do not represent a monophyletic group but a form taxon, since swans and geese are not considered...

s in the bird family Anatidae

Anatidae

Anatidae is the biological family of birds that includes ducks, geese and swans. The family has a cosmopolitan distribution, occurring on all the world's continents except Antarctica and on most of the world's islands and island groups...

.

It has two species, which are similar anatomically

Anatomy

Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...

 but quite distinct in external morphology

Morphology (biology)

In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

:

• Muscovy Duck
  Muscovy Duck
  The Muscovy Duck is a large duck which is native to Mexico and Central and South America. A small wild population reaches into the United States in the lower Rio Grande Valley of Texas...
  
  , Cairina moschata
  • Domesticated Muscovy Duck, Cairina moschata momelanotus sometimes Cairina momelanotus
• White-winged Duck, Cairina scutulata

These were initially placed as type genus in the "Cairininae" (or "Cairinini"), a supposed group of "perching duck

Perching duck

The perching ducks were previously treated as a small group of ducks in the duck, goose and swan family Anatidae, grouped together on the basis of their readiness to perch high in trees...

s" which was somewhat intermediate between dabbling ducks and shelduck

Shelduck

The shelducks, genus Tadorna, are a group of large birds in the Tadorninae subfamily of the Anatidae, the biological family that includes the ducks and most duck-like waterfowl such as the geese and swans....

s. However, this assemblage turned out to be paraphyletic, and the Cairina species were moved to the dabbling duck subfamily Anatinae

Anatinae

The Anatinae is a subfamily of the family Anatidae . Its surviving members are the dabbling ducks, which feed mainly at the surface rather than by diving...

, to which they seemed closest from the data available at that time.

Analysis of the mtDNA sequences

DNA sequence

The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...

 of the cytochrome b

Cytochrome b

Cytochrome b/b6 is the main subunit of transmembrane cytochrome bc1 and b6f complexes. In addition, it commonly refers to a region of mtDNA used for population genetics and phylogenetics.- Function :...

 and NADH dehydrogenase

NADH dehydrogenase

NADH dehydrogenase is an enzyme located in the inner mitochondrial membrane that catalyzes the transfer of electrons from NADH to coenzyme Q...

 subunit

Protein subunit

In structural biology, a protein subunit or subunit protein is a single protein molecule that assembles with other protein molecules to form a protein complex: a multimeric or oligomeric protein. Many naturally occurring proteins and enzymes are multimeric...

 2 gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

s (Johnson & Sorenson, 1999), meanwhile, has indicated that this is probably not correct, and that moreover the two species usually united in Cairina are not even closely related to each other, which is also suggested by the biogeography

Biogeography

Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...

 of their distribution:

The Muscovy Duck seems a distant relative to the genus Aix

Aix (genus)

Aix is a genus that contains two species of ducks: the Wood Duck , and the Mandarin Duck .The genus belongs to the family Anatidae in the waterfowl order Anseriformes...

which for example contains the North American Wood Duck

Wood Duck

The Wood Duck or Carolina Duck is a species of duck found in North America. It is one of the most colourful of North American waterfowl.-Description:...

. Together, they appear related to the shelducks and C. moschata would thus be placed in the Tadorninae

Tadorninae

The Tadorninae is the shelduck-sheldgoose subfamily of the Anatidae, the biological family that includes the ducks and most duck-like waterfowl such as the geese and swans....

.

The White-winged Wood Duck, on the other hand - which has sometimes been allied with the enigmatic Hartlaub's Duck

Hartlaub's Duck

The Hartlaub's Duck is a dark chestnut-coloured duck of African forests. Formerly included in the paraphyletic "perching duck" assemblage, it was later moved to the dabbling duck assemblage...

 (Madge & Burns, 1987) - should according to the molecular analysis moved to its old genus, Asarcornis, and could in fact be a peculiar diving duck

Diving duck

The diving ducks, commonly called pochards or scaups, are a category of duck which feed by diving beneath the surface of the water. They are part of the diverse and very large Anatidae family that includes ducks, geese, and swans....

.