Saxifraga is the largest genus in the family Saxifragaceae, containing more than 400 species of holarctic perennial plants, known as saxifrages or rockfoils. The Latin word Saxifraga means literally stone-breaker, from Latin Saxum (rock or stone) and Frangere (to break). It is usually thought to indicate a medicinal use for treatment of urinary calculi (known as kidney stones), rather than breaking rocks apart. Most saxifrages are smallish plants whose leaves grow close to the ground, often in a rosette. Saxifrages are typical inhabitants of Arctic-alpine ecosystems, and are hardly ever found outside the temperate parts of the Northern Hemisphere; most members of this genus are found in subarctic climates. A good number of species grow in glacial habitat. Various Saxifraga species are used as food plants by the caterpillars of some butterflies and moths, such as the Phoebus Apollo (Parnassius phoebus).