cactus genus of six species, family Cactaceae, native to Brazil, grown for its striking elongated flowers, unique in the family and adapted to pollination by hummingbirds. All grow perched on trees or shrubs, sometimes in shady places among rocks.

S. russelliana and S. truncata (long known as Zygocactus) have short flattened stem segments. The common Christmas cactus (S. buckleyi), blooming about Christmas time in the Northern Hemisphere, may be a hybrid of these two. The three remaining species, S. opuntioïdes, S. orssichiana, and S. obtusangula, have rounded stem segments but bear similar flowers.