The common names "Night-Blooming Cereus" and "Queen of the Night" both refer to several different cacti. "Orchid Cactus" is also a common name for Epiphyllum oxypetallum (although the San Diego Epiphyllum Society website notes that "the term 'orchid cactus' is almost completely dismissed as the plants are not related to orchids in any way"). "Queen of the Night" refers specifically to Selenicereus grandiflorus. Following is a list of species that are known by these names:
Ulf Eliasson (firstname.lastname@example.org) sent me the following message about nomenclature:
Epiphyllum is a genus of cacti where all species have flat leaflike stems -- they are not leaves. All species are epiphytic and root in the small amount of mould or moss in branch angles and so on. It is however very closely related to Selenicereus. Selenicereus mostly have angled stems, but there are species with entirely flat stems or with three angles. Selenicereus inermis of N South America might have flat stems and was once descripted as a new species of Epiphyllum by a botanist not realising that flat stems is not a precise feature. Selenicereus are also mainly epiphytic or growing on rocks; however several species grow well as a terrestrial (on the ground) plant as well.
Epiphyllum differs from Selenicereus (botanicly speaking) in spination of the flowers. Epiphyllum has no spines on the flower tube -- Selenicereus has. Epiphyllum has often no or very few hairs on the tube -- Selenicereus are often very hairy on the flower tube.
Hylocereus has always triangular stems, flowers with large bracts on the tube and few or none spines nor hairs. Often epiphytic or xerophytic.
This species is now classified as Selenicereus anthonyanus. Stems are Epiphyllum-like, but the flower is a typical Selenicereus-flower with spiny tube.
Some common names:
Have comments, corrections, suggestions, links? Email me (Glenn Rice) at email@example.com. Sorry, but I will not answer botanical/cultivation questions! Other websites have cultivation information; see my "links" section above for several good ones.