Schlumbergera


Schlumbergera is a small genus of cacti with six to nine species native to the coastal mountains of southeastern Brazil. These plants grow on trees or rocks in habitats that are generally shady with high humidity, and can be quite different in appearance from their desert-dwelling cousins. Most species of Schlumbergera have stems which resemble leaf-like pads joined one to the other and flowers which appear from areoles at the joints and tips of the stems. Two species have cylindrical stems more similar to other cacti.
Common names for these cacti generally refer to their flowering season. In the Northern Hemisphere, they are called Christmas cactus, Thanksgiving cactus, crab cactus and holiday cactus. In Brazil, the genus is referred to as Flor de Maio, reflecting the period in which they flower in the Southern Hemisphere. Most of the popular houseplants are cultivars of Schlumbergera, rather than species, with flowers in white, pink, yellow, orange, red or purple. The Easter cactus or Whitsun cactus, placed in the genus Rhipsalidopsis, is also called a holiday cactus and has flowers in red, orange, pink and white.
The cultivars of the Christmas cactus fall into two main groups:
  • The Truncata Group contains all cultivars with features derived mainly from the species S. truncata: stem segments with pointed teeth; flowers held more or less horizontally, usually above the horizontal, and whose upper side is differently shaped from the lower side ; and yellow pollen. They generally flower earlier than members of the Buckleyi Group and, although common names are not applied consistently, may be distinguished as Thanksgiving cactus, crab cactus or claw cactus.
  • The Buckleyi Group contains all cultivars with at least some features clearly showing inheritance from S. russelliana: stem segments with rounded, more symmetrical teeth; more or less symmetrical flowers which hang down, below the horizontal; and pink pollen. They generally flower later than members of the Truncata Group and are more likely to be called Christmas cactus.

    Description

In the wild, Schlumbergera species grow either on trees or on rocks and can form sizeable shrubs with woody bases; a height of up to has been reported for one species. They are leafless, the green stems acting as photosynthetic organs. The stems are composed of segments, which take one of two forms. In most species the segments are strongly flattened, being made up of a central core with two "wings". Special structures characteristic of cacti, called "areoles", then occur at the ends of the segments of the stem. In two species the stems are less flattened, more cylinder-shaped, and the areoles are arranged in a more or less spiral pattern all over the segments. In both cases, the areoles, which may have wool and bristles, are where the flower buds appear.
The flowers either hang downwards and are almost regular or, as in most species, are held more or less horizontally with the higher side of the flower different from the lower side. In those species whose flowers are held up, their angle with the horizontal is relatively constant and is characteristic of the species. Each flower has 20–30 tepals. The outer tepals are short and unconnected, and spread out or curve backwards. The inner tepals are longer and in most species become progressively more fused together at the base to form a floral tube. In some species the difference between the outer and inner tepals creates the appearance of a "flower within a flower". The flowers produce nectar in a chamber at the base of the floral tube.
In most species, the many stamens are arranged in two series, with the inner stamens being fused at the base to form a short tubular structure and the outer stamens arising from along the floral tube. The style is usually dark red and has a stigma with 6–8 lobes; the style plus stigma is roughly the same length as a stamen. If the flower is fertilized, a fleshy fruit forms, either smooth or with ribs. The brown or black seeds are about 1 mm in diameter.

Taxonomy

The genus is one of a small number belonging to a group of cacti classified as the tribe Rhipsalideae. Species of cacti belonging to this group are quite distinct in appearance and habit from most other cacti since they grow on trees or rocks as epiphytes or lithophytes. Although the species are easy to identify as members of the Rhipsalideae, for many years there was confusion as to how they should be divided into genera. This confusion extended to Schlumbergera, whose complicated taxonomic history has been detailed by McMillan and Horobin. The modern genus Schlumbergera was created by Charles Lemaire in 1858. The name commemorates Frédéric Schlumberger, who had a collection of cacti at his chateau near Rouen. Lemaire placed only one species in his new genus – a plant discovered in Brazil in 1837 which had been named Epiphyllum russellianum by William J. Hooker. Lemaire renamed it Schlumbergera epiphylloides.
Lemaire noted the similarity of his Schlumbergera epiphylloides to a species first described as Epiphyllum truncatum by Adrian Hardy Haworth in 1819, but did not accept that the two species should be included in the same genus. In 1890, Karl Moritz Schumann created the new genus Zygocactus, transferring Epiphyllum truncatum to Zygocactus truncatus. Although he later placed it back in Epiphyllum, abandoning Zygocactus, the generic name Zygocactus continued to be widely used.
In 1913, Nathaniel Britton and Joseph Rose followed Lemaire in keeping Schlumbergera russelliana and Zygocactus truncatus in separate genera. They also transferred the Easter cactus to Schlumbergera as S. gaertneri, initiating a lasting confusion between these two genera.
In 1953, Reid Venable Moran placed both Schlumbergera russelliana and Zygocactus truncatus in the genus Schlumbergera. Other species were added later by David Hunt, including those formerly placed in Epiphyllanthus.
Schlumbergera and Hatiora have long been confused. Species in the former genus generally have flowers that are zygomorphic with a distinct floral tube, while those in the latter have actinomorphic flowers with inconspicuous tubes. DNA data showed that as previously circumscribed the two genera are not monophyletic and the three species in Hatiora subgenus Rhipsalidopsis were transferred into Schlumbergera, although this change has not been universally adopted, with other sources placing two in the genus Rhipsalidopsis.

Synonymy

The following genera are now synonyms of Schlumbergera :
  • Epiphyllanthus A.Berger
  • Opuntiopsis Knebel
  • Zygocactus K.Schum.
  • Zygocereus Frič & Kreuz.
  • Epiphyllum Pfeiff. but not Epiphyllum Haw.
The case of Epiphyllum is complex. In 1753, Carl Linnaeus created the genus Cactus. As more species were discovered this proved too broad, and new genera were set up to subdivide the cacti. The genus Epiphyllum was created in 1812 by Haworth, based on Linnaeus's Cactus phyllanthus. In 1831, Johann Link created the genus Phyllocactus based on the same species. Following Ludwig Pfeiffer 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 are given in the list below.
  • Schlumbergera kautskyi N.P.Taylor
  • * syn. S. truncata subsp. kautskyi Horobin & McMillan
  • Schlumbergera microsphaerica Hoevel
  • * syn. Cereus microsphaerica K.Schum., Epiphyllanthus microsphaericus Britton & Rose, Cereus obtusangulus K.Schum., Epiphyllanthus obtusangulus A.Berger, Zygocactus obtusangulus Loefgr., S. obtusangula D.R.Hunt
  • Schlumbergera opuntioides D.R.Hunt
  • * syn. Epiphyllum opuntioides Loefgr. & Dusén, Zygocactus opuntioides Loefgr., Epiphyllanthus opuntioides Moran
  • Schlumbergera orssichiana Barthlott & McMillan
  • Schlumbergera russelliana Britton & Rose
  • * syn. Epiphyllum russellianum Hook., S. epiphylloides Lemaire, nom. illeg.
  • Schlumbergera truncata Moran
  • * syn. Epiphyllum truncatum Haw., Zygocactus truncatus 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 P.V.Heath
Two species that have been placed in Hatiora or Schlumbergera are placed in Rhipsalidopsis by Plants of the World Online as of 2023:
  • Rhipsalidopsis gaertneri Linding.
  • * syns. Hatiora gaertneri Barthlott, Schlumbergera gaertneri Britton & Rose
  • Rhipsalidopsis rosea Britton & Rose
  • * syns. Hatiora rosea Barthlott, Schlumbergera rosea Calvente & Zappi
Four hybrids of Schlumbergera s.s. have been named, all made in cultivation. 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 Tjaden = S. russelliana × S. truncata; S. Buckleyi Group
  • * syn. Epiphyllum buckleyi T.Moore, E. rollissonii T.Moore, S. bridgesii 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 Group