Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Core eudicots
Order: Caryophyllales
Family: Cactaceae
Subfamily: Cactoideae
Tribe: Pachycereeae
Genus: Peniocereus
(A.Berger) Britton & Rose
– Wikipedia     

Origin and Habitat: Tropical areas of southern Mexico (Guanajuato, Hidalgo, Jalisco, México, Michoacán, Morelos, Nayarit, Oaxaca, Puebla, Aguascalientes Querétaro and Sinoaloa), but now largely spreading around Mexico. It has also been naturalized in many regions, such as Australia and it is widely cultivated because of its flowers.
Habitat and Ecology: The species grows in tropical deciduous dry forest. There are no known major threats to this species.
Description: Peniocereus serpentinus is a fast-growing slender, shrubby columnar cactus that grows often in groups, erect at first sometimes climbing then leaning and sprawling all over and best tied to something so it wont fall and grow decumbent. It would be good for hanging baskets. This species is in need of taxonomic review as in Mexico it is recognized as a separate genus Nyctocereus; there is genetic evidence for this.
Flowers: When old enough it bears large, nocturnal flowers, they are funnelform, white with pinkish outside segments, 15 to 20 cm long (15 cm in diameter), pericarpel and flowers with bristles. The flowers are very fragrant, like gardenias.

Source: Encyclopedia of Cactii