in 1837, the European tradition was to use Phyllocactus for epiphytic cacti with large regular flowers and Epiphyllum for the irregular-flowered species now called Schlumbergera truncata. Under modern rules, Phyllocactus is an illegitimate name, as is Epiphyllum in the sense of Pfeiffer; thus Epiphyllum Pfeiff. is a synonym of Schlumbergera. The true genus Epiphyllum Haw. now has around 19 species. Species Between six and nine species are currently recognized. In the narrowest circumscription, Schlumbergera sensu stricto, six species are accepted. Only synonyms which have been widely used (and their basionyms) are given in the list below. Schlumbergera kautskyi (Horobin & McMillan) N.P.Taylor syn. S. truncata subsp. kautskyi Horobin & McMillan Schlumbergera microsphaerica (K.Schum.) Hoevel syn. Cereus microsphaerica K.Schum., Epiphyllanthus microsphaericus (K.Schum.) Britton & Rose, Cereus obtusangulus K.Schum., Epiphyllanthus obtusangulus (K.Schum.) A.Berger, Zygocactus obtusangulus (K.Schum.) Loefgr., S. obtusangula (K.Schum.) D.R.Hunt Schlumbergera opuntioides (Loefgr. & Dusén) D.R.Hunt syn. Epiphyllum opuntioides Loefgr. & Dusén, Zygocactus opuntioides (Loefgr. & Dusén) Loefgr., Epiphyllanthus opuntioides (Loefgr. & Dusén) Moran Schlumbergera orssichiana Barthlott & McMillan Schlumbergera russelliana (Hook.) Britton & Rose syn. Epiphyllum russellianum Hook., S. epiphylloides Lemaire, nom. illeg. Schlumbergera truncata (Haw.) Moran syn. Epiphyllum truncatum Haw., Zygocactus truncatus (Haw.) K.Schum., nom. illeg. In a wider circumscription, one species formerly placed in Hatiora is transferred into Schlumbergera. Schlumbergera lutea Calvente & Zappi, syn. Hatiora epiphylloides (Porto & Werderm.) P.V.Heath Two species that have been placed in Hatiora or Schlumbergera are placed in Rhipsalidopsis by Plants of the World Online : Rhipsalidopsis gaertneri (Regel) Linding. (Easter cactus, Whitsun cactus) syns. Hatiora gaertneri (Regel) Barthlott, Schlumbergera gaertneri (Regel) Britton & Rose Rhipsalidopsis rosea (Lagerh.) Britton & Rose syns. Hatiora rosea (Lagerh.) Barthlott, Schlumbergera rosea (Lagerh.) Calvente & Zappi Four hybrids of Schlumbergera s.s. have been named, all made in cultivation (although the first may possibly occur in the wild). The International Code of Nomenclature for Cultivated Plants recommends that cultivated plants should be named under its rules, not those appropriate for natural species and hybrids. The Group names given below were provided by McMillan and Horobin. Schlumbergera × buckleyi (T.Moore) Tjaden = S. russelliana × S. truncata; S. Buckleyi Group syn. Epiphyllum buckleyi T.Moore, E. rollissonii T.Moore, S. bridgesii (Lemaire) Loefgr. Schlumbergera × eprica Süpplie = S. orssichiana × S. russelliana Schlumbergera × exotica Barthlott & Rauh = S. truncata × S. opuntioides; S. Exotica Group Schlumbergera × reginae McMillan = S. truncata × S. orssichiana; S. Reginae