Sedum is a large genus of flowering plants in the family Crassulaceae, members of which are commonly known as stonecrops. The genus has been described as containing up to 600 species, subsequently reduced to 400–500. They are leaf succulents found primarily in the Northern Hemisphere, but extending into the southern hemisphere in Africa and South America. The plants vary from annual and creeping herbs to shrubs. The plants have water-storing leaves. The flowers usually have five petals, seldom four or six. There are typically twice as many stamens as petals. Various species formerly classified as Sedum are now in the segregate genera Hylotelephium and Rhodiola.
The Crassulaceae clades are alocated to tribes, as follows:
Clades and tribes within Sempervivoideae
Clades containing Sedum, shown in blue
Species allocated to Sedum are found within four of the six separate Crassulceae clades in the Sempervivoideae (Acre, Leucosedum, Aeonium and Sempervivum), while other distinct genera appear to be nested within Sedum. However the number of species found outside of the first two clades (Tribe Sedeae) are only a small fraction of the whole genus. Therefore the current circumscription, which is somewhat artificial and catch-all must be considered unstable. The relationships between the tribes of Sempervivoideae is shown in the cladogram.
There are now thought to be approximately 55 European species. Sedum demonstrates a wide variation in chromosome numbers, and polyploidy is common. Chromosome number is considered an important taxonomic feature.
Various attempts have been made to subdivide this large genus, in addition to segregating separate genera, including creation of informal groups, sections, series and subgenera. Gray (1821) divided the 13 species known in Britain at that time into five sections:
Berger (1930) defined 22 subdivisions, which he called Reihe (series). Some later authors have added other series, and combined some of the series into groups.
Later authors have recognised two subgenera, Gormania and Sedum.
Gormania: (Britton) Clausen. 110 species from Sempervivum, Aeonium and Leucosedum clades, from Europe and North America.
Sedum: 320 species from Acre clade, from Asia and the Americas.
Nikulin and colleagues (2016) have recommended that, given the monophyly of Aeonieae and Semperviveae, species of Sedum outside of the tribe Sedeae (all in subgenus Gormania) be removed from the genus and reallocated. However this does not resolve the problem of other genera embedded within Sedum, in Sedeae.
Of about 80 Eurasian species, series Rupestria forms a distinct monophyletic group of about ten taxa, which some authors have considered a separate genus, Petrosedum. It was series 20 in Berger's classification. Native to Europe it has escaped cultivation and become naturalized in North America.
Distributed in mainly in temperate to subtropical climates the Northern hemisphere, extending to the Southern hemisphere in Africa and South America, being most diverse in the Mediterranean, Central America, Himalayas, and East Asia.
Many sedums are cultivated as ornamentalgarden plants, due to their interesting and attractive appearance and hardiness. The various species differ in their requirements; some are cold-hardy but do not tolerate heat, some require heat but do not tolerate cold.
Sedum can be used to provide a roof covering in green roofs, where they are preferred to grasses. Ford's Dearborn Truck Plant's living roof has 454,000 square feet (42,200 m2) of sedum. Rolls-Royce Motor Cars plant in Goodwood, England, has a 242,000 square feet (22,500 m2) roof complex covered in Sedum, the largest in the United Kingdom. Nintendo of America's roof is covered in some 75,000 square feet (7,000 m2) of Sedum. The Javits Center in New York City is covered with 292,000 square feet (27,100 m2) of Sedum.
Gallo, Lorenzo (24 August 2017a). "Towards a review of the genus Petrosedum (Crassulaceae): Taxonomic and nomenclatural notes on Iberian taxa". Webbia. 72 (2): 207–216. doi:10.1080/00837792.2017.1363978.
Hart, H. 't; Jarvis, C. E. (May 1993). "Typification of Linnaeus's names for European species of Sedum subgen. Sedum". Taxon. 42 (2): 399–410. doi:10.2307/1223149. JSTOR1223149.
Ito, Takuro; Nakanishi, Hiroki; Chichibu, Yoshiro; Minoda, Kiyotaka; Kokubugata, Goro (9 June 2017). "Sedum danjoense (Crassulaceae), a new species of succulent plants from the Danjo Islands in Japan". Phytotaxa. 309 (1): 23. doi:10.11646/phytotaxa.309.1.2.
Nikulin, Vyacheslav Yu.; Gontcharova, Svetlana B.; Stephenson, Ray; Gontcharov, Andrey A. (September 2016). "Phylogenetic relationships between Sedum L. and related genera (Crassulaceae) based on ITS rDNA sequence comparisons". Flora. 224: 218–229. doi:10.1016/j.flora.2016.08.003.
Zika, Peter F.; Wilson, Barbara L.; Brainerd, Richard E.; Otting, Nick; Darington, Steven; Knaus, Brian J.; Nelson, Julie Kierstead (10 September 2018). "A review of Sedum section Gormania (Crassulaceae) in western North America". Phytotaxa. 368 (1): 1. doi:10.11646/phytotaxa.368.1.1.