A “Zygo Cactus” is not the same as a true Christmas Cactus, though the names are often confused in commerce. The term “Zygo Cactus” is typically a shortened version of the former genus name Zygocactus, which is now considered outdated in scientific classification. Both plants belong to the modern genus, Schlumbergera, which encompasses the group commonly known as holiday cacti. The plant most frequently sold under the name “Christmas Cactus” or “Zygo Cactus” is actually the Thanksgiving Cactus.
Defining the Key Players
The holiday cacti found in homes worldwide belong to the genus Schlumbergera, which are epiphytes native to the humid coastal mountains of Brazil. The true Christmas Cactus is botanically identified as Schlumbergera x buckleyi, a hybrid species created in the 1840s. This specific plant is less common in modern nurseries than its close relative, the Thanksgiving Cactus.
The plant most often referred to as a “Zygo Cactus” or “Christmas Cactus” is the Thanksgiving Cactus, Schlumbergera truncata. The name Zygocactus was historically used to classify this species, and the older term persists in gardening circles. Confusion is further compounded by the existence of the Easter Cactus, Rhipsalidopsis gaertneri, which blooms in the spring and is in a different but related genus.
Visual Identification
The most straightforward way to distinguish between the two holiday cacti is by examining their stem segments, which are flattened stems called cladodes. The Thanksgiving Cactus (S. truncata), often mistakenly called Zygo Cactus, has segments with distinct, pointed, saw-tooth or claw-like projections along the edges. These sharp-edged segments are the reason this plant is sometimes given the nickname “Crab Cactus.”
In contrast, the true Christmas Cactus (S. x buckleyi) possesses cladodes with much smoother, more rounded, or scalloped edges without the pronounced points. The flowers also offer a clear distinction between the two species when they bloom. The blooms of the Thanksgiving Cactus are held more horizontally and display a noticeable zygomorphic, or irregular, symmetry, meaning they are symmetrical along only one plane.
The flowers of the true Christmas Cactus hang more pendulously and exhibit a more radially symmetric appearance. Additionally, the Thanksgiving Cactus typically flowers earlier, starting around mid-November. The true Christmas Cactus tends to bloom later, closer to December and into January. This difference in bloom timing reflects the origin of their common names.
Distinct Care Requirements
While both the Thanksgiving Cactus and the true Christmas Cactus are tropical epiphytes that share similar care needs, the environmental triggers required for successful blooming differ slightly. Both types thrive in bright, indirect light and appreciate higher humidity levels. They require a specific combination of reduced light and cooler temperatures to initiate the formation of flower buds, a process called photoperiodism.
To encourage blooming, both species need a period of extended, uninterrupted darkness, typically 12 to 14 hours per night, for about six weeks in the fall. Any light exposure during the dark period can disrupt the signal to bloom, causing the plant to fail to set buds. This long night period must be paired with cooler temperatures, ideally a night temperature range of 50 to 60 degrees Fahrenheit.
The Thanksgiving Cactus, which naturally blooms earlier, is slightly more tolerant of warmer temperatures during the bud-setting phase. For the true Christmas Cactus, maintaining nighttime temperatures between 55 and 60 degrees Fahrenheit is often more effective for encouraging December blooms. During this pre-bloom period, a temporary reduction in watering also helps to mimic the dry season in their native habitat, signaling the plant to prepare for flowering.