Schlumbergera

This article is about the genus Schlumbergera, including the house plants commonly called Christmas cactus or Thanksgiving cactus. For the Easter cactus or Whitsun cactus, see Hatiora. For the desert Christmas cactus, see Cylindropuntia leptocaulis.

Schlumbergera
Cultivar belonging to the Schlumbergera Truncata Group
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Core eudicots
Order: Caryophyllales
Family: Cactaceae
Subfamily: Cactoideae
Tribe: Rhipsalideae
Genus: Schlumbergera
Lem.
Species
  • S. kautskyi (Horobin & McMillan) N.P.Taylor
  • S. microsphaerica (K.Schum.) Hoevel
  • S. opuntioides (Loefgr. & Dusén) D.R.Hunt
  • S. orssichiana Barthlott & McMillan
  • S. russelliana (Hook.) Britton & Rose
  • S. truncata (Haw.) Moran

Schlumbergera is a small genus of cacti with six species found in the coastal mountains of south-eastern Brazil. 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. In Brazil, the genus is referred to as Flor de Maio (May flower), reflecting the period in which they flower in the Southern Hemisphere.

This genus contains the popular house plants known by a variety of names including Christmas Cactus, Thanksgiving Cactus, Crab Cactus and Holiday Cactus, which are Schlumbergera cultivars, and flower in white, pink, yellow, orange, red or purple. (The Easter Cactus or Whitsun Cactus, which may also be called a Holiday Cactus and has vivid scarlet flowers in the most commonly grown form, is now placed in the genus Hatiora.) The cultivars of Schlumbergera fall into two main groups:

Etymology

Botanist Charles Lemaire (1801-1871) gave the name Schlumbergera to this genus in 1858, honouring Frédéric Schlumberger (1823-1893), French cactus and other succulent plant collector.[1]

Description

In the wild, the species of Schlumbergera grow either on trees (epiphytic) or on rocks (epilithic) and can form sizeable shrubs with woody bases; a height of up to 1.2 m (4 ft) has been reported for one species (S. opuntioides).[2] 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 (cladodes), being made up of a central core with two (or more rarely three) "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.[3]

Flower cut in half vertically with the base to the left; the bases of the tepals form a kind of tube, the upper parts bending away from the tube; the stamens run the full length of the flower from left to right and emerge from the end; some start at the very base of the flower, others start from further along to the right, being joined to a tepal.
Zygomorphic flower, probably of a cultivar in the S. Truncata Group, cut in half to show its internal structure

The flowers either hang downwards and are almost regular (radially symmetrical or actinomorphic) or, as in most species, are held more or less horizontally with the higher side of the flower different from the lower side (radially asymmetrical or zygomorphic). 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 – those closer to the base of the flower – are short and unconnected, and spread out or curve backwards. The inner tepals – those towards the tip of the flower – are longer and 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.[3]

The many stamens are arranged in two series, which is a distinctive characteristic of the genus. The inner stamens are fused at the base to form a short tubular structure. The outer stamens arise 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 the stamens. 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.[3]

Taxonomy

Drawing is probably of a pressed specimen as it appears flat; the base is at the bottom and the plant then branches repeatedly – about six times in the longest branch. Most branches end in either buds or regular flowers which are pinkish.
Drawing of S. russelliana, the type species, from the Botanical Magazine, 1839

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.[4] This confusion extended to Schlumbergera, whose complicated taxonomic history has been detailed by McMillan and Horobin.[1] 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 (under the current rules of botanical nomenclature it should have been called Schlumbergera russelliana, which is its current name).[1]

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,[5] 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.[1]

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 – now Hatiora gaertneri – to Schlumbergera as S. gaertneri, initiating a lasting confusion between these two genera.)[1]

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, to form the modern total of six full species and a number of hybrids.[1]

Synonymy

The following genera are now synonyms of Schlumbergera (i.e. they have no species not moved into Schlumbergera):[6]

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.[7] The true genus Epiphyllum Haw. now has around 19 species.[8]

Species

Six species are currently recognized.[9] Only synonyms which have been widely used (and their basionyms) are given in the list below.

Four hybrids have been named, all made in cultivation (although the first may possibly occur in the wild).[9][10] 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.[11] The Group names given below were provided by McMillan and Horobin.[12]

The Easter Cactus was at one time placed in Schlumbergera, but has flowers which are different in structure. See Hatiora gaertneri: Taxonomy.

Distribution, habitat and ecology

Map shows the coastline of south-east Brazil. A strip running roughly south-west to north-east along part of this coastline is coloured red. The red strip is about five times as long as wide and extends either side of Rio de Janeiro.
The distribution of Schlumbergera species is discontinuous within the red area.[13]

Schlumbergera occurs only in the coastal mountains of south-east Brazil, in the states of São Paulo, Rio de Janeiro, Minas Gerais and Espírito Santo. Sites where it has been found range from close to the Tropic of Capricorn northwards to 20°S, i.e. in the southernmost part of the tropics.[3] Plants grow at altitudes from 700 metres (2,300 ft) in the case of S. truncata to 2,780 metres (9,120 ft) in the case of S. microsphaerica,[14] either in the coastal moist forests or in rocky areas. The natural distribution of Schlumbergera species has become confused because European cultivars were deliberately introduced into some areas, including the Serra dos Órgãos National Park, by the Brazilian Agricultural Department, to compensate for over-collecting of wild plants.[15]

Because of their height and proximity to the Atlantic Ocean, the coastal mountains produce high altitude moist forests – warm moist air is forced upwards into higher, colder locations where it condenses. Schlumbergera species grow in habitats which are generally relatively cool, shaded and of high humidity. David Hunt describes collecting specimens in conditions of cloud, drizzle and overnight temperatures down to −4 °C (25 °F).[16] Plants are epiphytic or lithophytic, growing on moss-covered tree branches or in rock crevices, often in small pockets of substrate formed from decayed leaves and other vegetation.[17] S. microsphaerica is found at higher altitudes, above 2,200 metres (7,200 ft),[14] in barren rocky habitats,[16] and tolerates higher light levels.[18]

The flowers of Schlumbergera have adaptations for pollination by hummingbirds: tubular flowers with abundant nectar, and colours towards the red end of the spectrum. Most species require cross-pollination to set seed. The exceptions are S. kautskyi and S. microsphaerica; as noted above, the latter is found at higher altitudes where humming birds may be absent or less common.[19]

The fruits of Schlumbergera do not open spontaneously when ripe, and appear to be adapted for distribution by birds, which eat the seeds and pulp contained in the fruit. Birds have been observed removing seeds which had stuck to their beaks by rubbing them on tree branches, where the seeds might be able to germinate. Segments may also break off from the stems and take root, thus enabling plants to propagate vegetatively.[19]

Cultivation

History

A small portion of green stem is to the left. A yellow flower seen from the side extends to the right. Stamens and a style extend out of the flower. Running from left to right the flower tilts upwards. At the end of the flower the upper petals are only bent back a short way, whereas the lower petals are bent almost back on themselves.
S. Truncata Group 'Gold Charm'; note the very pointed teeth at the end of the segments, zygomorphic flowers held above the horizontal, and yellow pollen.

Schlumbergera truncata was in cultivation in Europe by 1818, and S. russelliana was introduced in 1839. The two species were deliberately crossed in England by W. Buckley resulting in the hybrid now called S. × buckleyi, first recorded in 1852. By the 1860s, a substantial number of cultivars (cultivated varieties) were available in a range of colours and habits, and were used as ornamental plants in "stoves" (heated greenhouses) and in houses, where they were popular for their autumn and winter flowering. Many cultivars were selected seedlings of S. truncata, but at least three S. × buckleyi hybrids were available, of which one, now called S. 'Buckleyi', is thought to be the original Christmas Cactus. By the early part of the 20th century, the genus had become less popular, and many of the early cultivars were lost.[20]

From around the 1950s onwards, breeding resumed in Europe, North America, Australia and New Zealand. New plants were produced by crossing among the species and existing cultivars of S. truncata, S. russelliana and the hybrid S. × buckleyi. Treatments which induced mutations were also used. The result was a wide range of flower colours which had not been available before, including the first true yellow to be sold commercially, S. 'Gold Charm' (which was a sterile triploid). Breeders aimed for plants which grew strongly, were upright at the point of sale rather than pendulous, had many flowers or buds, and were adapted to living as house plants.[20]

In the 1980s the species S. orssichiana was also used in crosses. The hybrid of S. truncata and S. orssichiana has been named S. × reginae or S. Reginae Group; one of the first cultivars was S. 'Bristol Queen'. S. opuntioides crosses have also been made, but have not resulted in commercially available cultivars.[20]

Modern cultivars

The picture shows a flower from more or less below. The tepals radiate outwards from the centre, more or less symmetrically. The petals nearest the viewer bend outwards less than those further away.
Member of the S. Buckleyi Group, viewed from below; rounded rather than pointed edges of the segments, pendant more or less regular flowers and pink pollen.

McMillan and Horobin have listed hundreds of modern European, North American and Australian cultivars, which they put into a number of cultivar groups:[21]

Attempts have also been made to classify cultivars by colour. A difficulty is that the flowers of many cultivars exhibit different colours depending on the temperature during bud formation and growth. In particular, temperatures below 14 °C (57 °F) produce pink tones in otherwise white and yellow cultivars, and deepen the colour in pink and red cultivars. The availability of iron to the plant has also been suggested to affect flower colour.[21]

In the United States, cultivars are propagated in large numbers for sale before Thanksgiving Day (the fourth Thursday in November). In Europe, plants are mainly sold later in the year, in the period before Christmas. A single Dutch grower (de Vries of Aalsmeer, the Netherlands) was reported in 1989 as producing 2,000,000 plants per year.[21]

The image illustrates the points made in the article. The top image shows four segments with the stem running horizontally from right to left. Their edges have either no teeth or small, rounded projections. The bottom image also shows four segments with the stem running horizontally from right to left. The segments have pointed teeth on a least one edge. Both stems have a prominent mid-rib to all the segments.
Variation in stem shapes in Schlumbergera cultivars: top – typical of the Buckleyi Group; bottom – typical of the Truncata Group
The image shows six flowers in yellow, orange, red, white, pink and purple.
Variation in flower colour in modern Truncata Group cultivars; there are also bi-coloured flowers
There is a short piece of stem visible to the right. A flower then points to the left. The flower appears to consist of one flower emerging from another; a white tube connects the lower part of the flower to the upper part. The tepals are white with pink-purple edges.
S. Reginae Group 'Bristol Queen'

Common names

Plants are offered for sale under a variety of common names. The earliest English common name was "Christmas Cactus". In Europe, where plants are largely produced for sale in the period before Christmas, this remains the most widely used common name in many languages for cultivars of all groups (e.g. Weihnachtskaktus in German,[22] Cactus de Noël in French,[23] and Cacto de Navidad in Spanish[24]). This is also the name used in Canada.[25] In the United States, where plants are produced for the Thanksgiving holiday in November, the name "Thanksgiving Cactus" is used; "Christmas Cactus" may then be restricted to cultivars of the Buckleyi Group,[26] particularly the very old cultivars such as 'Buckleyi'.[25] The name "Crab Cactus" (referring to the clawed ends of the stems) is also used for the Truncata Group.[27] "Link Cactus" is another common name, describing the way that the stems of the genus as a whole are made up of linked segments.[25] The name "Chain Cactus" is common in New Zealand, and may also refer to Hatiora species.[28]

The Easter Cactus or Whitsun Cactus is now placed in the genus Hatiora, but was at one time included in Schlumbergera (or one of its synonyms). The name "Holiday Cactus" has been used to include both Schlumbergera and Hatiora cultivars.[25]

Care of cultivars

A plant with green upright stems is growing in a blue pot. There are a few flowers and buds at the end of the stems, all more or less upright.
Young plant of a member of the S. Truncata Group; still upright and therefore more convenient for selling

When grown as house plants, Schlumbergera cultivars are said to be relatively easy to care for. McMillan and Horobin describe in detail their cultivation in both commercial and domestic conditions. Their specific recommendations include:[29]

Schlumbergera new growth. The upper view shows bright red new cladodes forming, the centre shows maturing growth, the lower view shows two aerial roots extending down

Pests and diseases

In cultivation, these plants have been described as "remarkably free from pests and diseases". Two significant insect pests are aphids on young shoots, buds and flowers, and root mealybugs which attack below soil level. Stems and roots can be rotted by diseases caused by fungi and similar organisms; these include infections by species of Fusarium (a fungus), and Phytophthora and Pythium (both water moulds). Approved chemical treatments can be used in the case of insect attack or these diseases.[30]

Aphids, mealybugs and other invertebrate pests can spread viruses. Symptoms vary with the species, but a loss of vigour is usual. Cactus virus X has been isolated from S. truncata. There is no treatment for virus diseases; it is recommended that infected plants be destroyed.[30]

References

  1. 1 2 3 4 5 6 McMillan & Horobin 1995, pp. 12–17
  2. ↑ McMillan & Horobin 1995, p. 26
  3. 1 2 3 4 McMillan & Horobin 1995, particularly pp. 18–19
  4. ↑ Anderson 2001, pp. 102, 375
  5. ↑ IPNI Plant Name Query Results for Zygocactus, The International Plant Names Index, retrieved 2011-11-12
  6. ↑ USDA, ARS, National Genetic Resources Program, Germplasm Resources Information Network - Query GRIN Taxonomy for Families and Genera, National Germplasm Resources Laboratory, Beltsville, Maryland, retrieved 2011-10-29
  7. ↑ Hunt, D.R. (1969), "Contributions to the Flora of Tropical America: LXXVII: A Synopsis of Schlumbergera Lem. (Cactaceae)", Kew Bulletin 23 (2): 255–263, doi:10.2307/4108963
  8. ↑ Anderson 2001, p. 286
  9. 1 2 Hunt, David, "Appendix I Names and synonyms of the species, subspecies and interspecific hybrids", Missing or empty |title= (help), in McMillan & Horobin 1995, pp. 78–80
  10. 1 2 IPNI Plant Name Query Results for Schlumbergera eprica, The International Plant Names Index, retrieved 2011-11-08
  11. ↑ Brickell, Chris D. et al. (eds) (2009), "International Code of Nomenclature for Cultivated Plants", Scripta Horticulturae (8th ed.) (International Society of Horticultural Science) 10: 1–184, ISBN 978-0-643-09440-6, Recommendation 1A, p. 5
  12. ↑ McMillan & Horobin 1995, p. 90
  13. ↑ McMillan & Horobin 1995, p. 11
  14. 1 2 Anderson 2001, pp. 622–625
  15. ↑ McMillan & Horobin 1995, p. 55
  16. 1 2 Hunt, David, "Appendix III Excerpts from a Brazilian diary", Missing or empty |title= (help), in McMillan & Horobin 1995, pp. 82–88
  17. ↑ McMillan & Horobin 1995, p. 64
  18. ↑ McMillan & Horobin 1995, pp. 67
  19. 1 2 McMillan & Horobin 1995, p. 49ff
  20. 1 2 3 McMillan & Horobin 1995, particularly pp. 56–63
  21. 1 2 3 McMillan, A.J.S.; Horobin, J.F.; Hunt, David, "Appendix IV Checklists of historic varieties and modern cultivars", Missing or empty |title= (help), in McMillan & Horobin 1995, pp. 89–145
  22. ↑ Weihnachtskaktus (Schlumbergera): Pflege & Vermehrung, Die grüne Welt, archived from the original on 2011-11-04, retrieved 2011-11-04
  23. ↑ Cactus de Noël, Schlumbergera, Au Jardin, archived from the original on 2011-11-04, retrieved 2011-11-04
  24. ↑ Cactus de acción de gracias, Cactus de Navidad, Cactus de pascua, Cacto de Navidad, Santa Teresita, Infojardin, archived from the original on 2011-11-04, retrieved 2011-11-04
  25. 1 2 3 4 Brunelle, Paul J. (2001), Recognition and Culture of the Holiday Cacti, Dalhousie University, archived from the original on 2011-11-04, retrieved 2011-11-04
  26. ↑ Perry, Leonard, The Thanksgiving Cactus, backyardgardener.com, archived from the original on 2011-11-04, retrieved 2011-11-04 External link in |publisher= (help)
  27. ↑ "Christmas cactus", Encyclopædia Britannica Online, Encyclopædia Britannica Inc., 2011, retrieved 2011-11-04
  28. ↑ Jury, Abbie. "Plant Collector: zygocactus or Schlumbergera (probably truncata hybrid)". Tikorangi The Jury Garden.
  29. ↑ McMillan & Horobin 1995, pp. 63–70
  30. 1 2 McMillan & Horobin 1995, pp. 74–77

Bibliography

External links

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