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Although poinsettia dominates flowering plant sales around the holiday season, there are alternative plants that deserve consideration. One such plant often is marketed as holiday cactus. Few plants seem to create as much confusion as this plant, at least when it comes to botanical nomenclature. If fact, holiday cacti usually are either Christmas or Thanksgiving cactus plants. The two are closely related and both are epiphytic, tropical cacti native to the coastal mountains of south-eastern Brazil, in the state of Rio de Janeiro.
Thanksgiving cactus normally begins flowering in mid to late November and continues into December. Other common names for Thanksgiving cactus are crab cactus and claw cactus. The names come from the pointed "teeth" that exist on the flattened, jointed stem segments botanically known as phylloclades. Its flowers, whose upper side is differently shaped from the lower side, are held slightly above the horizontal.
Alternatively, Christmas cactus normally begins to flower in mid to late December and continues flowering into January. The phylloclades of Christmas cactus are more rounded and do not have forward-pointing teeth. When young, both plants have an upright growth habit. As plants mature, their branches tend to arch downward resulting in a very graceful appearance. With age, the base of the stem become thick and woody, helping to support the weight of the younger stems and flowers.
The flowers of both cacti are similar in appearance. Each flower has 20-30 tepals. The latter is the term used when flower parts cannot easily be classified as either sepals or petals The outer tepals are short, unconnected and spread out or curve backwards. The inner ones - those towards the tip of the flower - are longer and usually become progressively more fused at the base to form a floral tube. The term "flower within a flower" often has been used to describe their appearance.
In nature, flower color ranges from deep pink to red. Today, named cultivars are available in colors of pink, purple, and deep red. Additionally, many cultivars bear bicolored pink, purple, or red with white flowers. If there is any confusion as to the identity of the plants, they can be separated from each other by flower structure. Flowers of the Thanksgiving cactus have anthers (male flower parts that bears pollen) which are yellowish in color, while Christmas cactus bears pink to purplish-brown anthers.
Taxonomically, the confusion between these two plants has been equally great, to put it mildly. Thanksgiving cactus, once called Epiphyllum truncatum and Zygocactus truncatus, is now named Schlumbergera truncata. Likewise, Christmas cactus at times also was incorrectly called by one of the two older botanical names. Now, its current accepted botanical name is Schlumbergera x buckleyi (a.k.a. Schlumbergera bridgesii) and is thought to be a hybrid between Schlumbergera truncata and Schlumbergera russelliana. The latter species has rounded opposed to toothed phylloclads and passes this morphological trait along to Schlumbergera x buckleyi.
Whatever the true identity of a holiday cactus, all require similar growing conditions and cultural needs to flower. At this time of the year (early December), those who have Thanksgiving cactus plants should see flower buds well-formed or in bloom. Christmas cactus plants should just now begin to show some small flower buds. If buds are not evident by this time, there may be few if any flowers this season.
Both Thanksgiving and Christmas cactus are tropical, epiphytic cacti and not the "desert types." Therefore, their needs are somewhat different from other cacti. Because they are epiphytes, in nature these cacti like to grow in tree crevices where branches develop. Their native habitat is somewhat shady and fairly humid. Although they cannot endure frost, the plants are endemic to higher altitudes and prefer cool temperatures, especially to develop flower buds. Flower buds will not develop when night temperatures are 70 degrees F or higher for extended periods of time. High night temperatures also may cause small buds to drop from plants purchased at a retail outlet. If possible, locate new plants in a cool room or close to a cool window. Never place them near hot air ducts or appliances that produce heat.
In addition to cool temperatures, flower bud initiation in these cacti is influenced by the length of day. In nature, they are short-day plants which means they set buds in response to a critical period of darkness (12 hours or more) each day. In essence, short-day species really are "long-night" plants. At cool night temperatures (50 to 60 degrees F) some flower buds will form even if the plants are not exposed to long nights. An example of the latter would be plants located in a room that is lighted well into the night. For optimum flower bud formation, however, cool temperatures and natural day lengths (short days) are best, beginning about mid-September. If exposure to these conditions is delayed, flowering also will be delayed.
A slight reduction in watering at the beginning of bud formation also is helpful to prompt flower bud initiation. However, plants should never be allowed to wilt. Epiphytic cacti need growing media high in organic matter with good drainage. If plants become wilted or shriveled even though adequate water has been provided, root rot is the likely cause. The latter usually results from overwatering. Fortunately, stem segments (phylloclades) of epiphytic cacti root easily. Therefore, even when a plant's roots have died, removing some stem sections from the plant and using them to start new plants is a good way to "salvage" the plant.
Properly cared for, both Thanksgiving and Christmas cactus can live for years, producing more flowers with each passing year. They often become "heirloom plants" that are passed down from one generation to the next. If you have not started this tradition in you family, now is a perfect time to start, since these cacti are readily available around the holiday shopping season.
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REVISED: December 3, 2021