Crassulaceae

The Crassulaceae (, from Latin crassus, thick), also known as the crassulas, the stonecrops or the orpine family, are a diverse family of flowering plants primarily characterized by succulent leaves and a form of photosynthesis known as crassulacean acid metabolism (CAM), in which plants photosynthesize in the daytime and exchange gases during the cooler temperatures of the night. The blossoms of crassulas generally have five floral parts. Crassulaceae are usually herbaceous, though there are some subshrubs, and relatively few trees or aquatic plants.

The Crassulaceae is a medium-sized family in the core eudicots clade, along with the order Saxifragales, whose diversity has made infrafamilial classification very difficult. The family includes approximately 1,400 species and 34–35 genera—depending on the circumscription of the genus Sedum—distributed over three subfamilies. Members of the Crassulaceae are found worldwide, though are mostly concentrated in the Northern Hemisphere and Southern Africa (where the most species are found). They are adapted to thrive in typically dry, arid (hot or cold) areas where water may be scarce, and richer, organic substrates may be at a minimum or nonexistent. The Sempervivum (houseleeks) of Central and Southern Europe, or the Orostachys (dunce-caps) of Asia, for example, grow in rocky crevices at higher elevations, where soil is at a minimum but precipitation, sun exposure, and winds may be intense; these plants have thus adapted to absorb water by having succulent leaves, despite living often on slopes or near-vertical cliff faces, from which water typically drains quickly. Their roots are adhesive and grip to any rock, dirt, wood or other surface they come into contact with, while also gleaning minerals from said material. Seedlings that may sprout near more permanent sources of water, such as pooling rainwater or seeps, may experience rot or discoloration over time, and not survive.