"Hylotelphium", "Phedimus", "Sedum" and "Sempervivum" are cultivated for rock gardens and for "green roofs". Sedum brevifolium is a slowly spreading succulent plant in the genus "Sedum". Sedum oreganum is a species of succulent plant of the genus "Sedum". Within Sempervivum, "Sedum" series "Rupestre" ("Petrosedum") has x=28. Aeonium includes some "Sedum" species with x=8, while the remaining taxa are x=18. Newton and Arkwright's common roof has varieties of sedum covering it. The Sempervivoideae contain many familiar horticultural plants, such as "Sedum". Like most other "Sedum" species, it has a prostrate, spreading habit. The plant life, which is a sedum species, helps to purify the air. It is a species of "Sedum" from the plant family Crassulaceae. Various species formerly classified as "Sedum" are now in the segregate genera "Hylotelephium" and "Rhodiola". Prior to this most species in Sedoideae were placed in genus "Sedum". But these taxa are quite distinct from Sedum morphologically. Some authors merge "Rhodiola" into "Sedum". This region includes about 300 species of Sedoideae, and most genera segregated from "Sedum".