Sempervivae [Sempervivaceae] Jussieu[2] The Crassulaceae (/ˈkræsjuːleɪsiːˌiː, -siˌaɪ/, from Latin crassus, thick), also known as the crassulas, the stonecrops or the orpine family, are a diverse family of dicotyledon angiosperms 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 Crassulaceae is a medium-sized, monophyletic family in the core eudicots clade, along with the order Saxifragales, whose diversity has made infrafamilial classification very difficult.

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.

Crassulaceae are mainly perennial, and have huge global economic importance as collectible specimens, and as indoor and outdoor garden plants.

Many species in the family, especially of the African genera, have highly unusual (for plants) and otherworldly appearances, often with interesting textures (fuzzy, hairy, spiky, scaly) or curious nodules or growths, all of which are typically the result of environmental adaptations, such as "fuzzy" Kalanchoe tomentosa utilizing its hairs as a sunscreen.

Well-known genera and species include the many forms of Crassula ovata ('Jade', 'Money Plant' or 'Friendship Tree'), Kalanchoe blossfeldiana (florists' or supermarket-kalanchoe); Cotyledon, such as 'Chalk Fingers' and 'Pig's Ear', Sempervivum such as cobweb houseleek (or hen-and-chicks) and S. calcareum, and Aeonium such as A. haworthii (and its popular variegate 'Kiwi'), A. arboreum, canariense, urbicum; Monanthes, Umbilicus (pennywort), Bryophyllum, Echeveria, Sedum and Dudleya.

[3][4] Most species are herbaceous leaf succulents, with regular 5 part (pentamerous or fivemerous) flowers, isomerous free carpels and one or two whorls of stamens.

The leaf shape is simple (rarely pinnate) and usually entire, or crenate to broadly lobed, sometimes dentate or more deeply incised, glabrous (smooth) or tomentose.

[6][7] Reproductive: The inflorescence is usually terminal to lateral with many-flowered thyrses of cymes, less commonly spikes, racemes or panicles, rarely few to single flowered and axillary.

[6][7][9][10] However, a number of genera (e.g. Sempervivum, Aeonium) are polymerous (3-32), have basally fused or partially fused corolla segments, where the petals may form a corolla tube of varying length (e.g. Kalanchoe, Cotyledon), or have only a single whorl of 5 stamens (e.g. Crassula, Tillaea),[11] while Sedum includes much of the morphological diversity within the family as a whole.

Of the subclades within Telephium, the first (Hylotelephium sensu Thiede & Eggli: Hylotelphium, Orostachys and Sinocrassula) has x=12, and of the Rhodiola clade Phedimus has x=16 and Umbilcus x=24, representing another episode of polyploidy.

[21][5] Molecular phylogenetics has shown that morphological characters and chromosome numbers are so labile in the family, with rampant polyploidy and aneuploidy, that they cannot be used reliably to infer evolution, even at low taxonomic levels, with few exceptions.

As a result, generic boundaries have been considered unclear with frequent intergradation of characteristics between taxa, which may represent recurrent adaptation to xeric habitats.

[9] Crassulaceae has been considered a part of the order Saxifragales by most modern authors, including Cronquist (1981),[21] Takhtajan (1987),[23] and Thorne (1992),[24] based on phenotypic features, but subsequently confirmed by molecular methods.

Here, 14 families are shown in a cladogram, according to the Angiosperm Phylogeny Website, situating Crassulaceae as sister to the Haloragaceae sensu lato, and thus forming one of two subclades of the core Saxifragales.

[25][1] Peridiscaceae Paeonia (Paeoniaceae) Altingiaceae Hamamelidaceae Cercidiphyllum (Cercidiphyllaceae) Daphniphyllum (Daphniphyllaceae) Crassulaceae Aphanopetalum (Aphanopetalaceae) Tetracarpaea (Tetracarpaeaceae) Penthorum (Penthoraceae) Haloragaceae s.s. Iteaceae (including Pterostemonaceae) Ribes (Grossulariaceae) Saxifragaceae Crassulaceae evolved approximately 100–60 million years ago in southern Africa with the two most basal phylogenetic branches (Crassula, Kalanchoe) representing the predominantly southern African members.

The Sempervivoideae subsequently dispersed north to the Mediterranean region, and from there to Eastern Europe and Asia (Sempervivum and Leucosedum clades), with multiple groups spreading over the three continents of the Northern Hemisphere.

For instance the North African S. jaccardianum and S. modestum (Aeonium) are a sister group to the endemic Macaronesian species in that clade.

[14] In a much more extensive treatment in 1828, he divided the Crassulaceae into the two groups, Isostemonae and Diplostemonae (i.e. haplostemony vs. obdiplostemony) on the basis of the number of staminal whorls.

[5] Berger's classification depended on biogeography and a number of morphological characteristics (primarily the number and arrangement of floral parts (haplostemonous androecia, polymery), the degree of sympetaly, and phyllotaxis)[4] which are now recognized as being of limited value due to extensive homoplasy, having evolved independently many times, and hence provides little useful information, only two of the subfamilies proving monophyletic.

Sedum refers to herbaceous, predominantly perennial species with alternate and entire leaves, a single subaxial hydathode and pentamerous obdiplostemous flowers with free petals.

:[32] The general phylogenetic topology described by 't Hart et al. (1995) was confirmed in a larger study of 112 species of Crassulaceae sampled from 33 genera, and all six recognized subfamilies, using the chloroplast gene matK.

[9] A similar conclusion was seen in a further but more focussed study of East Asian Sedoideae that examined the internal transcribed spacer (ITS) region of nuclear ribosomes of 74 taxa.

The boundaries between Kalanchoe, Bryophyllum and Kitchingia have remained unclear, and the latter two genera are more commonly treated as sections of Kalanchoe:[3][9][10][38] Sempervivoideae is the largest and taxonomically most complex subfamily, distributed in temperate climates, with about 20–30 genera, and divided into five tribes, of which Sedeae contains two distinct clades, Leucosedum and Acre:[3] The family Crassulaceae has a cosmopolitan distribution, particularly Crassula, though rare in South America and Australia,[5] predominantly in the temperate and subtropical regions of the Northern hemisphere and Africa.

Although their succulent leaves and Crassulacean acid metabolism allow them to adapt to a variable water supply, they are not found in true desert areas.

[40] All species of Kalanchoe are toxic, particularly to livestock in Australia and South Africa, where alternative forage is scarce, with the flowers containing the highest concentration of cardiotoxins, the active ingredient being bufadienolides (named for their digoxin-like effect on Bufo toads).

Illness in domestic pets has also been reported, Kalanchoe blossfeldiana being a popular Christmas time decorative household plant.