Rhipsalideae

The Rhipsalideae are a small tribe of cacti, comprising four genera (and around 60 species). They grow on trees (epiphytes) or on rocks (lithophytes), where they either hang down or form creeping or upright shrubs. Their flowers open in the day and remain open at night; they may be either radially symmetrical (regular) or bilaterally symmetrical (zygomorphic). The fruits are berry-like, fleshy with smallish seeds.

They are found mainly in the east of South America, with a centre of diversity in Bolivia, but some species occur in Central America and North America; one species, ''Rhipsalis baccifera'', also occurs in the Old World.

Taxonomy

Cacti belonging to the Rhipsalidae are quite distinct in appearance and habit from other cacti, growing on trees or rocks as epiphytes or lithophytes, and are thus easily distinguished. However, for many years there has been confusion as to how to divide the tribe into genera. For example, in 1858 Charles Lemaire recognized the distinctiveness of the species then called ''Epiphyllum russellianum'' by creating the genus ''Schlumbergera''. However he kept the only other species of ''Schlumbergera'' known at the time in a different genus. As another example, in 1923, Nathaniel Britton and Joseph Rose created the genus ''Hatiora''. Of the species known at the time, they placed two in ''Hatiora'' (''H. salicornioides'' and ''H. cylindrica''); they left ''H. gaertneri'' in ''Schlumbergera'' where they had placed it in 1913, and they placed ''H. rosea'' in a new genus, ''Rhipsalidopsis''. According to Anderson, the confusion among the Rhipsalideae was not clarified until work by Wilhelm Barthlott and Nigel Taylor in 1995.

Recent molecular phylogenetic studies have led to a slight modification of the approach taken by Barthlott and Taylor, since with their circumscriptions, ''Hatiora'' and ''Schlumbergera'' were not monophyletic. One hypothesis for the relationships between the genera is shown below. The yellow shading shows species formerly placed in ''Hatiora'', but which were moved by Calvente et al. to a more broadly defined ''Schlumbergera''.

An alternative approach uses the genus ''Rhipsalidopsis'' for the two species ''Schlumbergera rosea'' and ''Schlumbergera gaertneri'', which are treated as ''Rhipsalidopsis gaertneri'' and ''Rhipsalidopsis rosea''.

Genera

The genera included in the tribe are as follows, with species counts based on Plants of the World Online:
* ''Hatiora'' Britton & Rose – 3 species; synonyms include ''Epiphyllopsis'', ''Hariota'' DC non Andan., ''Rhipsalidopsis'' and ''Pseudozygocactus''; it has been included in ''Rhipsalis''
* '' Lepismium'' Pfeiff. – 6 species; synonyms include ''Acanthorhipsalis'', ''Lymanbensonia'', ''Pfeiffera''; it has been included in ''Rhipsalis''
* ''Rhipsalis'' Gaertn. – 43 species; synonyms include ''Erythrorhipsalis''; most species in the tribe have been placed here at one time or another
* ''Schlumbergera'' Lem. – 9 species; synonyms include ''Epiphyllanthus'', ''Epiphyllum'' Pfeiffer non. Haworth and ''Zygocactus''

File:Hatiora saliscornioides BlKakteenT95.jpg, Illustration of ''Hatiora salicornioides''
File:Lepismium cruciforme var anceps.jpg, '' Lepismium cruciforme''
File:Rhipsalis pilocarpa10.jpg, '' Rhipsalis pilocarpa'' fruit
File:Schlumbergera truncata (Exotic Flora Plate 20).jpg, Illustration of ''Schlumbergera truncata''

References

Bibliography

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{{Wikispecies, Rhipsalideae

Cactoideae
Caryophyllales tribes