The true Christmas cactus — the hybrid Schlumbergera x buckleyi — a long-lived epiphytic holiday cactus grown indoors almost everywhere for its arching, segmented stems and its rose-to-magenta flowers that open in mid-winter, around Christmas. It is worth getting the identity right, because most plants sold and labeled as 'Christmas cactus' are actually the Thanksgiving cactus, Schlumbergera truncata. You can tell the two apart by the edges of the flat stem segments and by when they bloom: the true Christmas cactus has rounded, scalloped segment margins and flowers a few weeks later, in mid-winter, while the Thanksgiving cactus has sharp, claw-like teeth and blooms from late fall into early winter. Unlike a desert cactus, this is a forest epiphyte that grows on tree branches in the Atlantic coastal forest of southeastern Brazil, so it wants bright indirect light, a free-draining mix, sparing water, and — to set its buds — cool nights and short days. A reassuring point that sets it apart from many houseplants: it is non-toxic to cats and dogs.