Blue oil fern

A species of lithophytic and epiphytic fern native to Southeast Asia, including Southern China, Vietnam, and Thailand, is the blue oil fern. Microsorum thailandicum (steerei), most recognised for its amazing blue foliage, originates from damp, shady jungles in limestone regions, where the blue leaves act as an adaptation to collect more light in these dim understory circumstances. However, they move quite slowly and need constant attention for a long time to appear their finest. That means you can't let them go several weeks without watering them (otherwise they'll start to drop leaves or stop growing altogether).