The term 'ROCK PLANT' can refer to two different organisms: Sedum (5 letters) and LICHEN (6 letters). Sedum is a genus of flowering plants in the family Crassulaceae, commonly known as stonecrops. They are succulent plants that typically grow in rocky areas and have thick, fleshy leaves. LICHEN is a composite organism consisting of a fungus and an alga living together in a symbiotic relationship. It is found in many different habitats, including on rocks, and is often used as an indicator of air quality.