''Peniocereus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of vining cacti, comprising about 18

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

, found from the southwestern

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

and

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

. They have a large underground tuber, thin and inconspicuous stems. Its name comes from the prefix ''penio-'' (from the Latin ''penis'', meaning ‘tail’) and '' Cereus'', the large genus from which it was split. Known as the desert night-blooming cereus, it also shares its common names of "

night-blooming cereus Night-blooming cereus is the common name referring to a large number of flowering ceroid cacti that bloom at night. The flowers are short lived, and some of these species, such as ''Selenicereus grandiflorus'', bloom only once a year, for a s ...

" and "queen of the night" with many other similar cacti.

Taxonomy

''Peniocereus'' was first described in 1905 by Alwin Berger as a subgenus of ''Cereus'' with a single species, ''Cereus greggii''. This taxon was elevated to the genus level as ''Peniocereus greggii'' by Britton and Rose in 1909. Later in 1974 an infrageneric classification was constructed based on morphological features that split ''Peniocereus'' into two subgenera: ''Peniocereus'' and ''Pseudoacanthocereus''. In 2005 a molecular phylogenetic study of the genus supported this split and showed that ''Peniocereus'' is not monophyletic.

Species

Species include:

Subgenus ''Peniocereus''

Molecular phylogeny supported the position of this subgenus within ''Echinocereeae''.

''Nyctocereus''

The 2005 molecular study showed that ''P. serpentinus'' is in ''Echinocereeae'' along with subgenus ''Peniocereus'', but suggests resurrecting the monotopic ''Nyctocereus'' as it is sister to ''Bergerocactus''.

Subgenus ''Pseudoacanthocereus''

Molecular phylogeny and morphological evidence suggests this subgenus is more closely related to ''Acanthocereus''.

References

Cactoideae genera Cacti of Mexico Cacti of the United States Flora of the Southwestern United States Flora of the Sonoran Deserts Night-blooming plants Taxa named by Alwin Berger Taxa named by Nathaniel Lord Britton Taxa named by Joseph Nelson Rose {{cactus-stub