Schlumbergera is a small genus of six to nine cacti in the family Cactaceae (order Caryophyllales), native exclusively to the coastal mountains of southeastern Brazil. Unlike the desert cacti with which they share a family, these plants grow as epiphytes on moss-covered tree branches or as lithophytes in rock crevices, in cool, shaded, high-humidity habitats shaped by Atlantic mist forests.
The stems are composed of jointed segments. In most species the segments are strongly flattened (cladodes) — a central core flanked by two or more wings — and flowers emerge from areoles at the joints and tips. In two species (S. microsphaerica and S. opuntioides) the stems are more cylindrical, resembling those of other cacti. Flowers carry 20–30 tepals; the inner tepals are progressively fused into a floral tube that holds a nectar chamber. Flower orientation varies by species: in most, blooms are held horizontally and are zygomorphic (bilaterally symmetrical); in others they hang and are nearly actinomorphic (radially symmetrical). The tubular form, abundant nectar, and red-to-pink colours are adaptations for pollination by hummingbirds. Fleshy fruits are distributed by birds that consume the pulp and wipe the sticky seeds onto tree branches.
The genus was established by Charles Lemaire in 1858, honouring Frédéric Schlumberger, a French cactus enthusiast. Its taxonomic history is complex: Schlumbergera has been variously merged with Zygocactus, Hatiora, and Epiphyllanthus, and molecular data have prompted several boundary revisions. In the narrowest circumscription six species are accepted; broader treatments include species transferred from Hatiora.
Schlumbergera is best known as the source of the Christmas cactus and Thanksgiving cactus, among the most widely grown houseplants in the world. Commercial cultivars — mostly derived from S. truncata, S. russelliana, and the hybrid S. × buckleyi — bear flowers in white, pink, yellow, orange, red, and purple and bloom in autumn and early winter in the Northern Hemisphere (spring in their native Southern Hemisphere range, where they are called Flor de Maio, "May flower").
Etymology
The genus name Schlumbergera commemorates Frédéric Schlumberger (1823–1905), a French amateur botanist and cactus collector who maintained a notable collection at his chateau near Rouen, France. Charles Lemaire coined the name in 1858 when he transferred a Brazilian epiphytic cactus discovered in 1837 into the new genus. The common names "Christmas cactus" and "Thanksgiving cactus" refer to the Northern Hemisphere flowering season of cultivated plants, while in Brazil the genus is known as Flor de Maio ("May flower") for its spring bloom.
Distribution
Schlumbergera is endemic to the coastal mountain ranges of south-east Brazil, known as the Mata Atlântica highlands, occurring in the states of São Paulo, Rio de Janeiro, Minas Gerais, and Espírito Santo. Plants grow at elevations ranging from approximately 700 m (S. truncata) to 2,780 m (S. microsphaerica), either in coastal moist forests or in exposed rocky habitats. The observed wild range spans from near the Tropic of Capricorn north to about 20°S; however, the natural distribution has been partly obscured by deliberate introductions of European-bred cultivars into areas such as Serra dos Órgãos National Park.
Ecology
In the wild, Schlumbergera grows as an epiphyte on moss-covered tree branches or as a lithophyte in rock crevices, usually in small pockets of decayed leaf litter and organic matter. Habitats are characterised by high humidity, shade, and relatively cool temperatures; collector David Hunt reported overnight temperatures as low as −4 °C at collection sites. S. microsphaerica, found above 2,200 m in barren rocky terrain, tolerates higher light levels than other species. Flowers are adapted for hummingbird pollination — tubular with abundant nectar and colours towards the red end of the spectrum — and most species require cross-pollination to set seed. Fruits are fleshy and bird-dispersed; birds have been observed wiping sticky seeds onto branches where they may germinate. Stem segments that detach can also root and propagate the plant vegetatively.
Cultivation
Schlumbergera cultivars have been grown as ornamental houseplants in Europe since at least 1818, when S. truncata first appeared in cultivation; S. russelliana followed in 1839. Deliberate crossing by W. Buckley in England produced S. × buckleyi (first recorded 1852), the plant that became known as the original Christmas cactus. By the 1860s a substantial range of cultivars existed; by the early 20th century interest had waned and many early cultivars were lost. Breeding resumed from the 1950s in Europe, North America, Australia, and New Zealand, yielding a wide spectrum of flower colours including the first true-yellow commercial cultivar, S. 'Gold Charm'. Modern breeding has also drawn on S. orssichiana (from the 1980s) to produce the Reginae Group. Cultivars are divided into the Truncata Group (earlier-blooming, zygomorphic flowers, yellow pollen) and the Buckleyi Group (later-blooming, more regular flowers, pink pollen). Plants thrive in cool, humid conditions with indirect light, mimicking their cloud-forest habitat.
History
The genus has a complex taxonomic history reflecting prolonged confusion about generic boundaries among epiphytic cacti. Charles Lemaire established Schlumbergera in 1858 for S. russelliana, but did not initially include the closely related S. truncata. In 1890 Karl Moritz Schumann placed the latter in a new genus Zygocactus, which remained in widespread use for decades despite being later abandoned. Britton and Rose (1913) kept the two segregate genera; Reid Moran finally united them under Schlumbergera in 1953, and David Hunt later added further species. More recently, DNA evidence showed that Hatiora (as then circumscribed) was non-monophyletic, prompting transfer of Hatiora subgenus Rhipsalidopsis species into Schlumbergera, though this change has not been universally adopted — Plants of the World Online retains two of those species in Rhipsalidopsis.
