The pencil cactus is actually a succulent Euphorbia from Africa, a small indoor tree of smooth, pencil-thin green stems that branch like coral. It grows quickly in a bright window and develops real presence as a floor plant.

Give it your sunniest spot and water sparingly, letting the soil dry completely between drinks; a gritty cactus mix keeps the roots happy. Keep it above freezing. Wear gloves when trimming, since the milky sap can irritate skin and eyes.