Zygocactus is a common name for Thanksgiving cactus (Schlumbergera truncata syn. Zygocactus truncata). It sells as "Christmas cactus," "Thankgiving cactus," and "holiday cactus" at various stores during the holidays. True Christmas cactus (Schlumbergera x buckleyi) is not heavily marketed. Thanksgiving cactus blooms in late November, while Christmas cactus blooms around Christmas, and cultivars vary. The tropical Thanksgiving cactus produces purple, pink or white blossoms in response to the cooler temperatures and shorter days in late fall. Thanksgiving cactus is winter-hardy in in U.S. Department of Agriculture plant hardiness zones 10 to 12, but it's most often grown as a houseplant. The small, flat green stem segments are smooth, except for the toothed edges. There are no spines such as seen on many desert cactuses. The flower buds form at the tips of the topmost segments.