Schlumbergera gaertneri

Schlumbergera gaertneri, formerly Hatiora gaertneri, is a species of epiphytic cactus which belongs to the tribe Rhipsalideae within the subfamily Cactoideae of the Cactaceae. Together with the hybrid with "S. rosea", Schlumbergera" × "graeseri, it is known as Easter cactus or Whitsun cactus and is a widely cultivated ornamental plant. It has received the Royal Horticultural Society's Award of Garden Merit.
Description.
"Schlumbergera gaertneri" is found in southeastern Brazil, in Paraná and Santa Catarina, at altitudes of .
As with other species of the genus, "S. gaertneri" grows on trees (epiphytic) or less often rocks (lithophytic) in sub-tropical rain forest. With maturity, it develops into a branching pendant leafless shrub with a woody base. The stems are made up of segments, most of which are flattened and which are the photosynthetic organs (cladodes) of the plant. Younger segments are dullish green, long and wide, with small notches on the margins. Structures characteristic of cacti, called areoles, form in these notches. Flowers form from areoles at the ends of the stems. These are scarlet in colour, long, radially symmetrical (actinomorphic), opening to a funnel shape with a maximum diameter of about . Red oblong fruits form after the flowers are fertilized.
Taxonomy.
Although cacti belonging to the tribe Rhipsalideae are quite distinct in appearance and habit from other cacti, as they grow on trees or rocks as epiphytes or lithophytes, for a long time there has been confusion as to how the species should be placed into genera. "Schlumbergera gaertneri" was first described in 1884 by Eduard von Regel as the variety "gaertneri" of "Epiphyllum russellianum" (now "Schlumbergera russelliana"). The name honours Joseph Gaertner. In 1889, William Watson elevated it to the full species "E. gaertneri" and in 1913, Nathaniel Britton and Josephy Rose transferred it to "Schlumbergera" as "S. gaertneri".
The relationship to "S. russelliana" was based on the appearance of the stems, made up of somewhat flattened segments with small teeth, and the radially symmetrical shape of the flowers. However, the deeper structure of the flower differs from other "Schlumbergera" species, which have a short floral tube at the base of the flower formed by fused petals, and stamens arranged in two distinct series, whereas "S. gaertneri" has separate petals and a single series of stamens. "S. gaertneri" was separated from "Schlumbergera" as "Rhipsalis gaertneri" by Friedrich Vaupel in 1925, after which it was successively transferred to "Epiphyllopsis" by Alwin Berger in 1929, "Rhipsalidopsis" by Reid Moran in 1953, and "Hatiora" by Wilhelm Barthlott in 1987. More recently, it has been restored to "Schlumbergera" as the result of molecular phylogenetic studies.
In horticultural sources, the Easter cactus continued to be referred to as "Schlumbergera gaertneri" (even when other sources placed it in "Hatiora"), and also as "Rhipsalidopsis gaertneri".
Cultivation.
Under the name Easter cactus or Whitsun cactus, "Schlumbergera gaertneri" is widely cultivated as an ornamental plant for its scarlet flowers. Its common names reflect the period in which it flowers in the Northern Hemisphere, namely late Spring. It has been artificially crossed with a pink-flowered species, "Schlumbergera rosea", to form the hybrid "S." × "graeseri", cultivars of which have flowers in a wider range of colours.
The Easter cactus is considered more difficult to grow than the Christmas or Thanksgiving cactus (other cultivars and hybrids of "Schlumbergera"). Recommendations for care include: