Schlumbergera - WikiHQ

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 ("May flower"), 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 (zygomorphic); 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 (regular) 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

thumb|Zygomorphic flower, probably of a cultivar in the Truncata Group, cut in half to show its internal structure|alt=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.

In the wild, Schlumbergera species grow either on trees (epiphytic) or on rocks (epilithic) and can form sizeable shrubs with woody bases; a height of up to has been reported for one species (S. opuntioides). 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.

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 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. 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 (under the current rules of botanical nomenclature it should have been called Schlumbergera russelliana, which is its current name). 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.

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).

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 |alt=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.]]

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. Its observed range extends from close to the Tropic of Capricorn northwards to 20°S. I.e. in the southernmost part of the tropics. 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.

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 . S. microsphaerica is found at higher altitudes, above ,

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 hummingbirds may be absent or less common.

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.

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 houseplants.

The Easter cactus or Whitsun cactus was placed in the genus Rhipsalidopsis , 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 Rhipsalidopsis cultivars.

Growing medium: Free-draining, humus-rich, somewhat acid growing media are used for commercial production, such as a mixture of peat or leafmould and an inert material such as grit, sharp sand or polystyrene beads. It is recommended that plants should be grown in relatively small pots; half-height pots are suitable.
Watering: They are more tolerant of drought than many house plants, though not as drought tolerant as the desert cactus. They can be damaged by both under- and over-watering. Keeping the growing medium just moist throughout the year avoids either extreme.
Light: They can be damaged by exposure to more than small amounts of sunlight. Members of the Buckleyi Group, such as the old-fashioned Christmas cactus with pendant flowers, are more tolerant of high light levels than members of the Truncata Group, such as most of the modern cultivars. Too much light causes stems to take on a reddish colouration; however, very low light levels will prevent flowering. Day length is important in controlling flowering; continuous darkness for at least 12 hours is necessary to induce bud formation. A period of about 8 days with 16 hours of darkness at has been shown to cause flower buds to form. Lower temperatures slow this process. The advice sometimes given to withhold water to produce flower buds has been shown to be incorrect.
Temperature: Holiday cacti grow best when they are placed in a location with partial shade, with a temperature between . They can not tolerate temperature less than 10 °C (50 °F).
Propagation: Both commercially and in the home, propagation can be achieved by using short pieces of stem, one to three segments long, twisted off rather than cut. Cuttings are allowed to dry for 1–7 days, forming a callus at the broken end, and then rooted in an open growing medium. Temperatures above and up to in long day/short night conditions speed rooting.

File:Schlumbergera IP.jpg|alt=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

File:Schlumbergera growth.jpg|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

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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.

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.

Bibliography

External links

Schlumbergera growing information, species, cultivar varieties, pictures and videos
Time-lapse video of Schlumbergera flower opening