| Schlumbergera | |
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| Cultivar belonging to theSchlumbergera Truncata Group | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Order: | Caryophyllales |
| Family: | Cactaceae |
| Subfamily: | Cactoideae |
| Tribe: | Rhipsalideae |
| Genus: | Schlumbergera Lem. |
| Species | |
Schlumbergera is a smallgenus ofcacti with six to nine species found in the coastal mountains of south-easternBrazil. These plants grow on trees or rocks in habitats that are generally shady with high humidity, and can be quite different in appearance from theirdesert-dwelling cousins. Most species ofSchlumbergera have stems which resemble leaf-like pads joined one to the other and flowers which appear fromareoles 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 calledChristmas cactus,Thanksgiving cactus,crab cactus andholiday cactus. In Brazil, the genus is referred to asFlor de Maio (May flower), reflecting the period in which they flower in the Southern Hemisphere. Most of the popular houseplants arecultivars ofSchlumbergera, rather than species, with flowers in white, pink, yellow, orange, red or purple. The Easter cactus or Whitsun cactus, placed in the genusRhipsalidopsis, 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:
In the wild, the species ofSchlumbergera 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).[1] They are leafless, the green stems acting asphotosynthetic 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.[2]
The flowers either hang downwards and are almost regular (radially symmetrical oractinomorphic) 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 orzygomorphic). 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 20–30tepals. 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 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 producenectar in a chamber at the base of the floral tube.[2]
In most species, the manystamens 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. Thestyle is usually dark red and has astigma with 6–8 lobes; the style plus stigma is roughly the same length as the stamens. If the flower isfertilized, a fleshyfruit forms, either smooth or with ribs. The brown or blackseeds are about 1 mm in diameter.[2]
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Thegenus is one of a small number belonging to a group of cacti classified as the tribeRhipsalideae. 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 asepiphytes orlithophytes. 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.[3] This confusion extended toSchlumbergera, whose complicated taxonomic history has been detailed by McMillan and Horobin.[4] The modern genusSchlumbergera was created byCharles Lemaire in 1858. The name commemorates Frédéric Schlumberger, who had a collection of cacti at his chateau nearRouen. Lemaire placed only one species in his new genus – a plant discovered in Brazil in 1837 which had been namedEpiphyllum russellianum byWilliam J. Hooker. Lemaire renamed itSchlumbergera epiphylloides (under thecurrent rules of botanical nomenclature it should have been calledSchlumbergera russelliana, which is its current name).[4]
Lemaire noted the similarity of hisSchlumbergera epiphylloides to a species first described asEpiphyllum truncatum byAdrian 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 genusZygocactus,[5] transferringEpiphyllum truncatum toZygocactus truncatus. Although he later placed it back inEpiphyllum, abandoningZygocactus, the generic nameZygocactus continued to be widely used.[4]
In 1913,Nathaniel Britton andJoseph Rose followed Lemaire in keepingSchlumbergera russelliana andZygocactus truncatus in separate genera. They also transferred the Easter cactus toSchlumbergera asS. gaertneri, initiating a lasting confusion between these two genera.[4]
In 1953,Reid Venable Moran placed bothSchlumbergera russelliana andZygocactus truncatus in the genusSchlumbergera. Other species were added later byDavid Hunt, including those formerly placed inEpiphyllanthus.[4]
Schlumbergera andHatiora 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 previouslycircumscribed the two genera are notmonophyletic and the three species inHatiora subgenusRhipsalidopsis were transferred intoSchlumbergera,[6] although this change has not been universally adopted, with other sources placing two in the genusRhipsalidopsis.[7][8]
The following genera are now synonyms ofSchlumbergera (i.e. they have no species not moved intoSchlumbergera):[9]
The case ofEpiphyllum is complex. In 1753,Carl Linnaeus created the genusCactus. As more species were discovered this proved too broad, and new genera were set up to subdivide the cacti. The genusEpiphyllum was created in 1812 by Haworth, based on Linnaeus'sCactus phyllanthus. In 1831,Johann Link created the genusPhyllocactus based on the same species. FollowingLudwig Pfeiffer in 1837, the European tradition was to usePhyllocactus for epiphytic cacti with large regular flowers andEpiphyllum for the irregular-flowered species now calledSchlumbergera truncata. Under modern rules,Phyllocactus is an illegitimate name, as isEpiphyllum in the sense of Pfeiffer; thusEpiphyllumPfeiff. is a synonym ofSchlumbergera.[10] The true genusEpiphyllumHaw. now has around 19 species.[11]
Between six and nine species are currently recognized.[8][12] In the narrowestcircumscription,Schlumbergerasensu stricto, six species are accepted. Only synonyms which have been widely used (and theirbasionyms) are given in the list below.
In a wider circumscription, one species formerly placed inHatiora is transferred intoSchlumbergera.[6][8]
Two species that have been placed inHatiora orSchlumbergera are placed inRhipsalidopsis byPlants of the World Online as of January 2023[update]:[13]
Four hybrids ofSchlumbergera s.s. have been named, all made in cultivation (although the first may possibly occur in the wild).[14][15] TheInternational Code of Nomenclature for Cultivated Plants recommends that cultivated plants should be named under its rules, not those appropriate for natural species and hybrids.[16] The Group names given below were provided by McMillan and Horobin.[17]
Schlumbergera occurs only in the coastal mountains of south-eastBrazil, in the states ofSão Paulo,Rio de Janeiro,Minas Gerais andEspírito Santo. Sites where it has been found range from close to theTropic of Capricorn northwards to20°S, i.e. in the southernmost part of the tropics.[2] Plants grow at altitudes from 700 metres (2,300 ft) in the case ofS. truncata to 2,780 metres (9,120 ft) in the case ofS. microsphaerica,[19] either in thecoastal moist forests or in rocky areas. The natural distribution ofSchlumbergera species has become confused because European cultivars were deliberately introduced into some areas, including theSerra dos Órgãos National Park, by the Brazilian Agricultural Department, to compensate for over-collecting of wild plants.[20]
Because of their height and proximity to the Atlantic Ocean, the coastal mountains producehigh 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).[21] 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.[22]S. microsphaerica is found at higher altitudes, above 2,200 metres (7,200 ft),[19] in barren rocky habitats,[21] and tolerates higher light levels.[23]
The flowers ofSchlumbergera have adaptations for pollination byhummingbirds: tubular flowers with abundant nectar, and colours towards the red end of the spectrum. Most species requirecross-pollination to set seed. The exceptions areS. kautskyi andS. microsphaerica; as noted above, the latter is found at higher altitudes where hummingbirds may be absent or less common.[24]
The fruits ofSchlumbergera 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 topropagate vegetatively.[24]
Schlumbergera truncata was in cultivation in Europe by 1818, andS. russelliana was introduced in 1839. The two species were deliberately crossed in England by W. Buckley resulting in thehybrid now calledS. ×buckleyi, first recorded in 1852. By the 1860s, a substantial number ofcultivars (cultivated varieties) were available in a range of colours and habits, and were used as ornamental plants in "stoves" (heatedgreenhouses) and in houses, where they were popular for their autumn and winter flowering. Many cultivars were selected seedlings ofS. truncata, but at least threeS. ×buckleyi hybrids were available, of which one, now calledS. '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.[25]
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 ofS. truncata,S. russelliana and the hybridS. ×buckleyi. Treatments which inducedmutations 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 steriletriploid). 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.[25]
In the 1980s the speciesS. orssichiana was also used in crosses. The hybrid ofS. truncata andS. orssichiana has been namedS. ×reginae orS. Reginae Group; one of the first cultivars wasS. 'Bristol Queen'.S. opuntioides crosses have also been made, but have not resulted in commercially available cultivars.[25]
McMillan and Horobin have listed hundreds of modern European, North American and Australian cultivars of the Christmas cactus, which they put into a number of cultivar groups:[26]
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.[26]
In the United States, cultivars are propagated in large numbers for sale beforeThanksgiving Day (the fourth Thursday in November). In Europe, plants are mainly sold later in the year, in the period beforeChristmas. A single Dutch grower (de Vries ofAalsmeer, the Netherlands) was reported in 1989 as producing 2,000,000 plants per year.[26]
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,[27]cactus de Noël in French,[28] andcacto de Navidad in Spanish[29]). This is also the name used in Canada.[30] 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,[31] particularly the very old cultivars such as 'Buckleyi'.[30] In Russia they are known asdekabrist ("decembrist") androzhdestvennika ("nativity"). The name "crab cactus" (referring to the clawed ends of the stems) is also used for the Truncata Group.[32] "Link cactus" is another common name, describing the way that the stems of the genus as a whole are made up of linked segments.[30] The name "chain cactus" is common in New Zealand, and may also refer toHatiora orRhipsalidopsis species.[33]
The Easter cactus or Whitsun cactus was placed in the genusRhipsalidopsis as of January 2023[update], but was at one time included inSchlumbergera (or one of its synonyms). The name "holiday cactus" has been used to include bothSchlumbergera andRhipsalidopsis cultivars.[30]
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:[34]
In cultivation, these plants have been described as "remarkably free from pests and diseases". Two significant insect pests areaphids on young shoots, buds and flowers, and rootmealybugs which attack below soil level. Stems and roots can be rotted by diseases caused by fungi and similar organisms; these include infections by species ofFusarium (afungus), andPhytophthora andPythium (bothwater moulds). Approved chemical treatments can be used in the case of insect attack or these diseases.[38]
Aphids, mealybugs and other invertebrate pests can spreadviruses. Symptoms vary with the species, but a loss of vigour is usual.Cactus virus X has been isolated fromS. truncata. There is no treatment for virus diseases; it is recommended that infected plants be destroyed.[38]
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