The Hylocereeae are a tribe of cacti. Most are found in the tropical forests of Central and northern South America, and are climbers or epiphytes, unlike most cacti. The tribe includes between six and eight genera in different circumscriptions. The plants known as "epiphyllum hybrids" or "epiphyllums", widely grown for their flowers, are hybrids of species within this tribe, particularly Disocactus, Pseudorhipsalis and Selenicereus, less often Epiphyllum, in spite of the common name.[2]
The members of the tribe are very variable in their morphology, especially when the terrestrial Acanthocereus is included. Many species form aerial roots. The hylocereoid clade (Selenicereus, Weberocereus and probably Aporocactus) are mostly climbing or epiphytic, and have spiny ribbed stems. The phyllocactoid clade (Epiphyllum, Disocactus, Kimnachia and Pseudorhipsalis) are mainly epiphytic, and have spineless flattened leaf-like stems. Flowers and pollination syndromes are equally diverse, ranging from large white nocturnal flowers to bright red flowers opening in the daytime.[3][4]
The group was first identified by Britton and Rose in 1920 as the subtribe Hylocereinae of the tribe Cereeae (subtribe Hylocereanae of tribe Cereanae in their terminology).[1][5] In 1958, Buxbaum revised the subtribe Hylocereinae, placing it in a newly created tribe Hylocereeae,[1] which included four other subtribes, some containing genera removed from Hylocereinae, others containing different genera.[6]
The International Cactaceae Systematics Group classification, based on Barthlott & Hunt (1993), recognized six genera within the tribe.[4][7] Subsequent studies suggested a number of changes, for example including Acanthocereus in the tribe and excluding Strophocactus (which had been sunk into Selenicereus). It was also shown that Hylocereus was nested within Selenicereus.[8] A major molecular phylogenetic study of the tribe was published in 2017. The lefthand cladogram below shows the relationships obtained (using the authors' circumscriptions of the genera and tribe).[3] A 2020 phylogenetic study, which also included morphological features of the stem, produced the righthand cladogram below. This resolved the position of Aporocactus, placing it within the hyloceroid clade, but left relationships within the phyllocactoid clade unresolved.[9]
The authors of the 2017 study proposed revised circumscriptions of some of the genera and of the tribe to make them monophyletic according to their molecular phylogeny:[3]
As of March 2021[update], the acceptance of some of these genera varied. For example, Plants of the World Online accepted Aporocactus[10] and the sinking of Hylocereus into Selenicereus,[11] but did not accept Kimnachia.[12]