Originally described by
Saint-Hilaire (1805) as Crassuleae, and therefore has his name as the
botanical authority. Authority has also, at times, been given to
De Candolle (DC), who first used the term "Crassulaceae" in 1815. He later placed the family among the
Dicotyledons. One of the most complete treatments was
Alwin Berger's revision in 1930. At that time the family comprised about 1,500 species, distributed over six subfamilies and 33 genera.
Circumscription of the family has remained relatively stable, with the exception of the placement of the genus
Penthorum and
Tetracarpaea, which has at times been placed either in their own
monogeneric family, Penthoraceae and Tetracarpaeaceae, or in the
Saxifragaceae. When Penthorum and Tetracarpaea were separated from Crassulaceae, they became a natural monophyletic group. Some later authors, such as
Cronquist, included only 900 species. Thiede and Eggli (2007), in their treatment of the family, describe 34 genera with about 1,410 species. The size of the genera varies considerably, from
Sedum, the largest with 300–500 species, to the smallest, which are
monotypic. Estimates of the number of species has varied between 1500 (Berger 1930) and 900 (Cronquist 1981).
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. For instance
Prometheum and
Rosularia have been segregated from
Sedum by their basic chromosome numbers. Crassulaceae is a medium size
monophyletic grouping within the
core eudicots. Originally considered a primitive member of the
Rosidae, in the order
Saxifragales, it is now placed, with that order as a
superrosid under the classification system of the
Angiosperm Phylogeny Group. There, the Saxifragales are a
sister group to the
rosids. Classification within the family is difficult and complex because many of the species hybridize readily, both in the wild and in cultivation, and the family is
morphologically,
cytologically and geographically diverse. As a result, generic boundaries have been considered unclear with frequent intergradation of characteristics between
taxa, which may represent recurrent adaptation to xeric habitats.
Genera 39 genera are accepted. •
Adromischus •
Aeonium •
Afrovivella •
Aichryson •
Chaloupkaea •
Chazaroa •
Chiastophyllum •
Cotyledon •
Crassula •
Cremnophila •
Dudleya •
Echeveria •
Graptopetalum •
Hylotelephium •
Hypagophytum •
Jeronimoa •
Kalanchoe •
Kungia •
Lenophyllum •
Meterostachys •
Monanthes •
Orostachys •
Pachyphytum •
Perrierosedum •
Petrosedum •
Phedimus •
Pistorinia •
Prometheum •
Pseudosedum •
Quetzalcoatlia •
Rhodiola •
Rosularia •
Sedum •
Sempervivum •
Sinocrassula •
Thompsonella •
Tylecodon •
Umbilicus •
Villadia Phylogeny Crassulaceae has been considered a part of the order
Saxifragales by most modern authors, including
Cronquist (1981),
Takhtajan (1987), and
Thorne (1992), based on
phenotypic features, but subsequently confirmed by molecular methods. The place of Crassulaceae within Saxifragales has varied over time, as molecular data accumulates. The number of families within Saxifragales varies depending on the delimitation of individual families. 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.
Biogeography and evolution 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. Other sources suggest that Crassulaceae evolved approximately 70 million years ago together with Haloragaceae
sensu lato (
Penthoraceae,
Haloragaceae). The family is considered to have had a gradual evolution, with a
basal split between Crassuloideae and the rest of the family (Kalanchoideae, Sempervivoideae). 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. Two lineages from the European Crassulaceae eventually dispersed to North America and underwent subsequent diversification. The Aeonium clade dispersed from northern Africa to adjacent Macaronesia. Distinct centers of
speciation developed in Macaronesia (Aeonium clade), Mexico (
Sedum and Echeverioideae in clade 7), and southeastern Asia (
Sedum sarmentosum, and
S. morissonensis in Acre clade). On arrival in the Northern hemisphere the Sempervivoideae reached its greatest diversity. Conversely, few representatives of the Crassulaceae occur in South America and Australia.
Sedum species are found in most of these regions, generally grouped with genera endemic to that region. For instance the North African
S. jaccardianum and
S. modestum (Aeonium) are a sister group to the endemic Macaronesian species in that clade. The Macaronesian archipelago appears to have been reached by Crassulaceae at least three times. Once by the ancestor of
Aeonium and
Monanthes, most likely from the Western Mediterranean region, with the closest extant relatives of these two genera (
Sedum caeruleum,
S. pubescens), coming from this region (Aeonium clade). The second migration was by an ancestor of a clade of three
Sedum species (
S. nudum,
S. lancerotense and
S. fusiforme (Acre clade)), which appear to have originated in Mexico. The third occurrence likely involved the ancestor of a lineage within the genus
Umbilicus (Rhodiola clade). The Macronesian flora include three genera from the Sempervivoideae,
Aeonium,
Aichryson and
Monanthes (Aeonium clade), together with several
Sedum spp. and one species of
Umbilicus (Rhodiola). North America was reached at least twice, once by an ancestor of
Parvisedum and
Dudleya, and once by a subclade of Acre. For a mapping of morphological features and biogeography on the phylogenetic tree, see Fig. 3. Chromosome numbers have played a limited role in elucidating evolution, but suggest a core of x=8, with subsequent polyploidy. For a mapping of chromosome numbers on the phylogenetic tree, see Fig. 4.
Subdivision History When
Carl Linnaeus published his
Species Plantarum in 1753 only a few genera, included in the modern
circumscription of Crassulaceae were described; the
type genus Crassula (10 species),
Tillaea (3),
Cotyledon (6),
Sempervivum (6),
Rhodiola (1) and
Sedum (15). By 1777,
Rhodiola had been submerged into
Sedum, only to be separated again in the twentieth century. While the family can fairly easily be recognised, identifying its constituent genera has been far more problematic. For an extensive history of subfamily Sedoideae, see . Saint-Hilaire's original description in 1805 included seven genera, as did De Candolle (1815). 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. The former corresponded to the modern Crassuloideae. Two lineages, six subfamilies, and 33 genera of Crassulaceae were described by Berger in 1930: Lineages, subfamilies, biogeography,
No. genera,
type genus (No. species in genus) • Crassula (Southern hemisphere) • Crassuloideae S Africa
5 Crassula (300) • (
Crassula,
Dinacria,
Rochea,
Vauanthes,
Pagella) • Kalanchiodeae S Africa, Madagascar
3 Kalanchoe (200) • (
Kalanchöe,
Bryophyllum,
Kitchingia) • Cotyledonoideae S Africa, Mediterranean
6 Cotyledon (30) • (
Cotyledon,
Adromischus,
Umbilicus,
Chiastophyllum,
Pistorina,
Mucizonia) • Sedum (Northern hemisphere) • Echeveroideae Mexico
5 Echeveria (150) • (
Echeveria,
Villadia,
Altamiranoa,
Pachyphytum,
Lenophyllum) • Sempervivoideae Mediterranea, Macaronesia
5 Sempervivum (25) • (
Sempervivum,
Aeonium,
Greenovia,
Monanthes,
Aichryson) • Sedoideae N hemisphere, S America, N & E Africa
11 Sedum (500) • (
Sedum (since including
Diamorpha),
Rosularia,
Orostachys,
Pseudosedum,
Hypagophytum,
Afrovivella,
Sempervivella,
Sinocrassula) Each of these contained one of the largest genera. Though various revisions since have proposed simpler schemes, such as Borisova (1939, revised 1969). Berger's classification has proven practical and been the most widely used, although some of the subfamilies are polyphyletic. 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) 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. Berger used sympetaly to define the group of Kalanchiodeae, Cotyledonoideae and Echeveroideae, but it also occurs in taxa within Crassuloideae and Sedoideae. Berger also placed all species with polymery into his Sempervivoideae, but it occurs in two different clades, Sempervivum and Aeonium. Although five of his six subfamilies appeared to be morphologically and geographically defined, the Sedoideae were problematic, being an artificial construction containing all
taxa which could not be fitted into the other subfamilies (
catch-all). Sedoideae contained three centres of diversity, East Asia, the Mediterranean region and North America, with the greatest in E. Asia. Only a few taxa, such as
Rhodiola and
Hylotelephium, occurring in all three regions. About 120 species were found in Europe and adjacent parts of North Africa and West Asia, and 400 in Eastern and central Asia. Within Sedoideae, the large cosmopolitan typical genus
Sedum (ca. 500 species), accounts for much of these issues, together with several smaller genera.
Sedum refers to herbaceous, predominantly perennial species with alternate and entire leaves, a single subaxial
hydathode and pentamerous obdiplostemous flowers with free petals. Most systematic treatments of the genus have resulted in conflicting classifications and evolutionary relationships within the Sedoideae. Attempts to resolve this have followed two opposing positions,
lumping and splitting. Either accepting one artificial large catch-all
polyphyletic genus,
sensu lato (
Sedum s.l.), or splitting it into many smaller genera,
sensu stricto (
Sedum s.l.). In the 1930s, Berger represented the splitting school of thought segregating genera such as
Orostachys,
Rosularia,
Pseudosedum and
Sempervivella. In contrast, Fröderströmm favoured retaining a broader construct of
Sedum, recognising only
Pseudosedum. In more recent times Ohba (1978) proposed the narrower view, segregating
Rhodiola,
Hylotelephium and
Prometheum, among other genera. Ohba then subdivided the old world taxa of his now reduced
Sedum into five subgenera: • subgenus
Aizoon • subgenus
Balfouria • subgenus
Spathulata • subgenus
Sedum • subgenus
Telmissa Grulich (1984) continued this process, proposing
Aizopsis (subgenus
Aizoon),
Asterosedum (subgenus
Spathulata),
Petrosedum (subgenus
Sedum series
Rupestria) and
Oreosedum (subgenus
Sedum series
Alba) as separate genera. As many as 32 segregate genera have been published, and most Eurasian crassulacean species were originally included in
Sedum, but subsequently segregated (
see Sempervivoideae). Subsequently, various revisions have proposed fewer subfamilies.
Takhtajan (1987) initially submerged Sempervivoideae in Sedoideae and Cotyledonoideae in Kalanchiodeae to produce four, but later (1997) only three, Crassuloideae, Kalanchoideae and Sedoideae.
Thorne (1992) also proposed three (Sedoidea, Cotyledonoidea, Crassuloidea), and then two (2000), Crassuloideae and Sempervivoideae.
Molecular phylogenetics Prior to the use of molecular methods of classification, attempts to replace Berger's system were largely unsuccessful. Subsequently, Hart and colleagues (1995) proposed two subfamilies, based on
molecular phylogenetic data with
chloroplast DNA, based on 49 species in 26 genera, which identified seven clades, named for constituent genera or species. Hart utilized a hierarchical system of subfamilies, tribes and subtribes, based on molecular, geographical and morphological criteria, including
embryology,
pollen morphology and
phytochemistry. • Subfamily Crassuloideae Berger Type:
Crassula 2 South African genera (250 species) • Subfamily Sedoideae Berger Type:
Sedum • Tribe Kalanchoeae 't Hart Type:
Kalanchoe 5 S African genera (250 spp.) • Tribe Sedeae 't Hart Type:
Sedum • Subtribe Telephiinae 't Hart Type:
Hylotelephium 8 Asian genera (150 spp.) • Subtribe Sedinae 't Hart Type:
Sedum 18 Northern hemisphere genera (700 spp.) The basal split at subfamily level, separates the
haplostemonous (single series of stamens, equal in number to petals) African Crassuloideae with opposite leaves, from the Sedeae without these characteristics (
obdiplostemonous, two whorls of stamens, twice as many as petals). These clades were (1–7): • Crassula/Crassuloideae, the
basal divergence, corresponds to Berger's subfamily of that name and are haplostemonous, but this feature is homoplasious. Confined to southern Africa, except for aquatic species, which are cosmopolitan. • Kalanchoe/Kalanchoeae, the second divergence, corresponds to Berger's Kalanchoideae (
Kalanchoe,
Bryophyllum,
Kitchingia) and the 2 S. African members of Cotyledonoideae (
Adromischus,
Cotyledon), together with
Tylecodon which was segregated from
Cotyledon in 1978. It was characterized by 4- or 5-merous flowers,
connate petals and seeds, together with
leaves that are flat, crenate or dentate (toothed), often petiolate and decussate. Chromosome number x=9. Within the clade,
Adromischus forms the basal divergence, followed by
Cotyledon/
Tylecodon as sister to
Kalanchoe. • Telephium/Telephiinae include members of Cotyledonoideae (
Umbilicus), together with some Sedoideae genera (including
Hylotelephium) and two of Ohba's five subgenera of
Sedum (
Aizoon and
Spathulata) and are usually obdiplostemonous, 5-merous flowers with free petals, flat and often crenate or dentate leaves ("flat leaved Asian
Sedum") and have
tubers, tuberous roots or woody or thickened
rhizomes (
monopodial or sympodial). In this respect many species share leaf features with the Kalanchoeae and Hart considered that the Telephiinae "bridge the gap" between the African Kalanchoeae and the Northern hemisphere Sedinae. Distribution predominantly East Asia, with
Umbilicus being Mediterranean. • Sempervivum includes the montane/alpine Eurasian
Sempervivum, its nominative genus, together with
Sedum from the same region, including
Sedum series
Rupestria.
Sempervivum is closely related to
Jovibarba, which some authors place within the former genus. • Leucosedum, i.e. "White Sedum", from
Sedum album, is polygeneric and includes additional Cotyledonoideae and Eurasian Sedoideae, including
Sedum album and other species of
Sedum subgenus
Gormania. The other genera are thought to have evolved from the Sedum lineage in this clade, including
Dudleya and
Sedella (N America) and
Rosularia,
Prometheum and
Pistorina (Eurasia). This grouping of 5–7 genera accounts for about 200 species. Some
Sedum subgenus
Sedum species also place here. Leucosedum species are found throughout the arid southwest United States and Mexico, as well as Eurasia. • Aeonium is predominantly Macaronesian Sempervivoideae (
Aeonium,
Aichryson,
Greenovia and
Monanthes), from a N African ancestor, and N. African
Sedum. Berger grouped the genera of that subfamily on the basis of polymerous flowers, but this is not restricted to this clade. • Acre, with about 7 genera and 500 species is the most taxon rich clade in the Crasulaceae. It includes the American subfamily Echeveroideae and
Sedum from Asia, Europe and Macaronesia, Mexico and Africa, including
Sedum acre and
Sedum subgenus
Sedum. The strong representation of
Sedum in this large clade accounts for it comprising a third of the diversity of the family. Two subclades consist of the N American and Macaronesian taxa, the other Eurasian. The last subtribe, the Sedinae, represents the last four clades (4–7) and contained half of the genera and species of Crassulaceae, including
Sedum, which is represented in all four clades, and the bulk of clades 5 and 7. In addition to
Sedum, 16 other genera are recognised. Aeonium is basal divergence, followed by Sempervivum, with Leucosedum and Acre as sister groups. The Sedinae were very diverse, making phenotypic circumscription impossible. A similar problem exists for each of its subclades. Given the realisation that
Sedum s.l. was a highly artificial construction, there was support for reducing it by describing a number of segregate genera. Ohba (1995) proposed that
Sedum s.s. should be restricted to clade 7, or at most clades 5–7, continuing some of the premolecular work in this direction, newly describing a number of Asian genera in addition to this reduced
Sedum.: •
Hylotelephium •
Orostachys •
Aizopsis •
Phedimus •
Rhodiola •
Prometheum •
Rosularia •
Balfouria •
Sinocrassula •
Meterostachys •
Pseudosedum 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. The Telephium clade, which had only been weakly supported, was seen as probably containing several subclades. 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. This region includes about 300 species of Sedoideae, and most genera segregated from
Sedum. However the Telephium clade of Ham was recognised as actually consisting of four separate clades, of which the two largest were named Hylotelephium and Rhodiola. The former are distinguished by being autumn flowering, while the remaining Sedeae bloom in spring and early summer. This analysis also confirmed the separate identity of most of the genera previously segregated from
Sedum. A second ITS study of 69 taxa in ten Asian genera resolved Telephium into just these two larger clades. Hart's taxonomic classification was revised by Thiede and Eggli (2007) to define three molecularly defined subfamilies, corresponding to the major
clades, Crassuloideae, Kalanchoöideae and Sempervivoideae, and 34 genera. Although some authors prefer the older term Sedoideae for Sempervivoideae, Sempervivoideae has taxonomic priority. The earliest branching subfamily is the Crassuloideae (2 genera), followed by the Kalanchoöideae (4 genera). Both of these represent the genera of southern Africa. The remaining six clades are
segregated into the five tribes of the large temperate climate subfamily Sempervivoideae, with about thirty genera. These are Telephiae, Umbilicicae, Semperviveae, Aeonieae and Sedeae. Sedeae is the largest of these and contains two
sister clades, Leucosedum and Acre. The Sempervivoideae contain many familiar horticultural plants, such as
Sedum. The phylogenetic relationships between the subfamilies are shown in the cladogram.
Subfamilies ===== Crassuloideae
Burnett ===== Crassuloideae is the smallest subfamily, representing a single monophyletic clade (Crassula), defined by
haplostemonous androecia (characterized by a single
whorl of
stamens, the number of which equals the number of
sepals,
petals and
carpels, and alternating with the petals). Although cosmopolitan in distribution, the center of diversity is southern Africa, with only the aquatic species being found more widely. It consists of two genera and about 250–300 species (Berger's other four genera (
Dinacria,
Pagella,
Rochea,
Vauanthes) having been subsumed into a larger
Crassula s.l.). Crassula is morphologically diverse and up to 20 sections based on phenotypic features have been described. One of these,
Tillaea, has at times been considered a separate genus.
Hypagophytum is a monotypic genus, alternatively considered under
Sempervivoideae. •
Crassula L. (including
Tillaea L.) c. 200 spp. •
Hypagophytum A.Berger 1 sp. ===== Kalanchoöideae
A.Berger ===== Kalanchoöideae is the next smallest subfamily, characterised by flower parts in fours. It represents Berger's Kalanchiodeae and Cotyledonoideae, in part. It is distributed in Madagascar and tropical Africa, with four genera and about between 130–240 species. It is characterised by fused corollas, chromosome number x=9 and mostly southern African distribution. The boundaries between
Kalanchoe,
Bryophyllum and
Kitchingia have remained unclear, and the latter two genera are more commonly treated as sections of
Kalanchoe: •
Adromischus Lem. •
Cotyledon L. •
Kalanchoe Adans. (including
Bryophyllum Adans.,
Kitchingia Adans.) •
Tylecodon Toelken ===== Sempervivoideae
Arn. ===== 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: • Telephieae • Umbiliceae • Semperviveae • Aeonieae • Sedeae == Distribution and habitat ==