Saxifragales is an
orderIn scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of
flowering plantThe flowering plants or angiosperms are the most diverse group of land plants. The flowering plants and the gymnosperms are the only extant groups of seed plants...
s. Their closest relatives are a large eudicot group known as the
rosidsThe rosids are a large group of flowering plants, containing about 70,000 species, more than a quarter of all angiosperms. It is divided into 16 to 20 orders, depending upon circumscription and classification. These orders, in turn, together comprise about 140 families...
by the
definitionIn taxonomy, circumscription is the definition of the limits of a taxonomic group of organisms. One goal of taxonomy is to achieve a stable circumscription for every taxonomic group. Achieving stability can range from simple or difficult....
of rosids given in the APG II
classification systemThe history of plant systematics—the biological classification of plants—stretches from the work of ancient Greek to modern evolutionary biologists. As a field of science, plant systematics came into being only slowly, early plant lore usually being treated as part of the study of...
. Some authors define the rosids more widely, including Saxifragales as their most
basalIn phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
group. Saxifragales is one of the eight groups that compose the core eudicots. The others are
GunneralesGunnerales is an order of flowering plants. In the APG II system it contains two genera: Gunnera and Myrothamnus. These may both be assigned to the same family or to two separate families...
,
DilleniaceaeDilleniaceae is the botanical name for a family of flowering plants. Such a family has been universally recognized by taxonomists. It is known to gardeners for the genus Hibbertia, which contains many commercially valuable garden species....
,
rosidsThe rosids are a large group of flowering plants, containing about 70,000 species, more than a quarter of all angiosperms. It is divided into 16 to 20 orders, depending upon circumscription and classification. These orders, in turn, together comprise about 140 families...
,
SantalalesSantalales is an order of flowering plants with a cosmopolitan distribution, but heavily concentrated in tropical and subtropical regions.Most have seeds without a testa, which is unusual for flowering plants...
,
BerberidopsidalesBerberidopsidales Doweld is a botanical name at the rank of order. This name is only newly published: such an order has been recognized by very few taxonomists. The APG II system, of 2003, merely mentions the possibility of recognizing the order, as...
,
CaryophyllalesCaryophyllales is an order of flowering plants that includes the cacti, carnations, amaranths, beets/chard/buckwheat/rhubarb, ice plants, tamarisks and most carnivorous plants. Many members are succulent, having fleshy stems or leaves.-Description:...
, and
asteridsIn the APG II system for the classification of flowering plants, the name asterids refers to a clade .Most of the taxa belonging to this clade had been referred to the Asteridae in the Cronquist system and to the Sympetalae in earlier systems...
.
Saxifragales has an extensive
fossilFossils are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous rock formations and sedimentary layers is known as the fossil record...
record.
Saxifragales is an
orderIn scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of
flowering plantThe flowering plants or angiosperms are the most diverse group of land plants. The flowering plants and the gymnosperms are the only extant groups of seed plants...
s. Their closest relatives are a large eudicot group known as the
rosidsThe rosids are a large group of flowering plants, containing about 70,000 species, more than a quarter of all angiosperms. It is divided into 16 to 20 orders, depending upon circumscription and classification. These orders, in turn, together comprise about 140 families...
by the
definitionIn taxonomy, circumscription is the definition of the limits of a taxonomic group of organisms. One goal of taxonomy is to achieve a stable circumscription for every taxonomic group. Achieving stability can range from simple or difficult....
of rosids given in the APG II
classification systemThe history of plant systematics—the biological classification of plants—stretches from the work of ancient Greek to modern evolutionary biologists. As a field of science, plant systematics came into being only slowly, early plant lore usually being treated as part of the study of...
. Some authors define the rosids more widely, including Saxifragales as their most
basalIn phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
group. Saxifragales is one of the eight groups that compose the core eudicots. The others are
GunneralesGunnerales is an order of flowering plants. In the APG II system it contains two genera: Gunnera and Myrothamnus. These may both be assigned to the same family or to two separate families...
,
DilleniaceaeDilleniaceae is the botanical name for a family of flowering plants. Such a family has been universally recognized by taxonomists. It is known to gardeners for the genus Hibbertia, which contains many commercially valuable garden species....
,
rosidsThe rosids are a large group of flowering plants, containing about 70,000 species, more than a quarter of all angiosperms. It is divided into 16 to 20 orders, depending upon circumscription and classification. These orders, in turn, together comprise about 140 families...
,
SantalalesSantalales is an order of flowering plants with a cosmopolitan distribution, but heavily concentrated in tropical and subtropical regions.Most have seeds without a testa, which is unusual for flowering plants...
,
BerberidopsidalesBerberidopsidales Doweld is a botanical name at the rank of order. This name is only newly published: such an order has been recognized by very few taxonomists. The APG II system, of 2003, merely mentions the possibility of recognizing the order, as...
,
CaryophyllalesCaryophyllales is an order of flowering plants that includes the cacti, carnations, amaranths, beets/chard/buckwheat/rhubarb, ice plants, tamarisks and most carnivorous plants. Many members are succulent, having fleshy stems or leaves.-Description:...
, and
asteridsIn the APG II system for the classification of flowering plants, the name asterids refers to a clade .Most of the taxa belonging to this clade had been referred to the Asteridae in the Cronquist system and to the Sympetalae in earlier systems...
.
Saxifragales has an extensive
fossilFossils are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous rock formations and sedimentary layers is known as the fossil record...
record. The extant members are apparently remnants of a formerly
diverseBiodiversity is the variation of life forms within a given ecosystem, biome, or for the entire Earth. Biodiversity is often used as a measure of the health of biological systems...
and
widespreadIn biogeography, cosmopolitan distribution is a state of being found almost anywhere around the world. A cosmopolitan biological category, e.g. genus, may be called a cosmopolite.Examples of cosmopolitan species:* Humans* House dust mite...
order.
Saxifragales, as it is now understood, is based upon the results of molecular phylogenetic studies of
DNA sequenceA DNA sequence or genetic sequence is a succession of letters representing the primary structure of a real or hypothetical DNA molecule or strand, with the capacity to carry information as described by the central dogma of molecular biology....
s. It is not part of any of the
classification systemsBiological systematics is the study of the diversification of life on the planet Earth, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...
based on
plant morphologyPlant morphology is the general term for the study of the morphology of plants. This is usually considered distinct from plant anatomy, which is the study of the internal structure of plants, especially at the microscopic level...
. The group is much in need of
comparative anatomicalComparative anatomy is the study of similarities and differences in the anatomy of organisms. It is closely related to evolutionary biology and phylogeny .-Description:Two major concepts of comparative anatomy are:...
studyResearch can be defined to be search for knowledge or any systematic investigation to establish facts. The primary purpose for applied research is discovering, interpreting, and the development of methods and systems for the advancement of human knowledge on a wide variety of scientific matters of...
, especially in light of the recent expansion of the family
PeridiscaceaePeridiscaceae is a family of flowering plants in the order Saxifragales. It comprises four genera: Medusandra, Soyauxia, Peridiscus, and Whittonia. It has a disjunct distribution, with Peridiscus occurring in Venezuela and northern Brazil, Whittonia in Guyana, Medusandra in Cameroon, and...
to include
Medusandra, a genus that before 2009, had usually not been placed in Saxifragales.
The order is divided into
suprafamilialIn biological classification, rank is the level in a taxonomic hierarchy. The most basic rank is that of species, the next most important is genus, and then family...
groups as shown on the
phylogenetic treeA phylogenetic tree or evolutionary tree is a tree showing the evolutionary relationships among various biological species or other entities that are believed to have a common ancestor. In a phylogenetic tree, each node with descendants represents the most recent common ancestor of the...
below. These groups are informal and are not understood to have any particular
taxonomic rankIn biological classification, rank is the level in a taxonomic hierarchy. The most basic rank is that of species, the next most important is genus, and then family...
.
Families
Saxifragales contains about 2470 species. These are distributed into 15 families, or into 12 families if
HaloragaceaeHaloragaceae is a family in the order of Saxifragales, of dicotyledon flowering plants. In the Cronquist system, it was included in the order Haloragales, but in the APG II system, it is placed in Saxifragales.- Distribution :...
sensu lato is recognized as a family consisting of Haloragaceae sensu stricto,
PenthorumPenthorum is a genus of plants in the order Saxifragales. They are erect herbaceous perennials about half a meter tall. The genus consists of two species, one from east Asia and one from eastern North America. It is variously classified in the family Saxifragaceae or its own family Penthoraceae....
,
Tetracarpaea, and
AphanopetalumAphanopetalum is a genus of twining shrubs or vines which are endemic to Australia.The genus is placed alone in family Aphanopetalaceae, which is in turn now placed in order Saxifragales...
. About 95% of the species are in five families:
CrassulaceaeThe Crassulaceae, or orpine family, is a family of dicotyledons. They store water in their succulent leaves. They are found worldwide, but mostly occur in the Northern Hemisphere and southern Africa, typically in dry and/or cold areas where water may be scarce...
(1400),
SaxifragaceaeSaxifragaceae is a plant family with about 460 known species in 36 genera. In Europe there are 12 genera.The flowers are hermaphrodite and actinomorphic...
(500), Grossulariaceae (150 - 200),
HaloragaceaeHaloragaceae is a family in the order of Saxifragales, of dicotyledon flowering plants. In the Cronquist system, it was included in the order Haloragales, but in the APG II system, it is placed in Saxifragales.- Distribution :...
(150), and
HamamelidaceaeThe Hamamelidaceae is a family of flowering plants in the order Saxifragales, including 27 genera and about 80-90 species, all shrubs and small trees...
(100). Most of the families are monogeneric. The number of genera in each family is as follows:
CrassulaceaeThe Crassulaceae, or orpine family, is a family of dicotyledons. They store water in their succulent leaves. They are found worldwide, but mostly occur in the Northern Hemisphere and southern Africa, typically in dry and/or cold areas where water may be scarce...
(34),
SaxifragaceaeSaxifragaceae is a plant family with about 460 known species in 36 genera. In Europe there are 12 genera.The flowers are hermaphrodite and actinomorphic...
(33),
HamamelidaceaeThe Hamamelidaceae is a family of flowering plants in the order Saxifragales, including 27 genera and about 80-90 species, all shrubs and small trees...
(27),
HaloragaceaeHaloragaceae is a family in the order of Saxifragales, of dicotyledon flowering plants. In the Cronquist system, it was included in the order Haloragales, but in the APG II system, it is placed in Saxifragales.- Distribution :...
(8),
PeridiscaceaePeridiscaceae is a family of flowering plants in the order Saxifragales. It comprises four genera: Medusandra, Soyauxia, Peridiscus, and Whittonia. It has a disjunct distribution, with Peridiscus occurring in Venezuela and northern Brazil, Whittonia in Guyana, Medusandra in Cameroon, and...
(4),
AltingiaceaeAltingiaceae is a small family of flowering plants in the order Saxifragales. They are wind-pollinated trees that produce hard, woody fruits containing numerous seeds. The fruits have been studied in considerable detail. They naturally occur in Central America, Mexico, eastern North America,...
(3),
IteaceaeIteaceae is a flowering plant family of trees and shrubs native to the eastern USA, south eastern Africa, and south and Southeastern Asia. Some taxonomic systems place the genera in this family in the Grossulariaceae.-References:...
(2), Paeoniaceae (1), Cercidiphyllaceae (1), Daphniphyllaceae (!),
AphanopetalaceaeAphanopetalaceae is a family of vine-like shrubs native to Australia. The family comprises two species, Aphanopetalum clematideum, endemic to limestone cliffs of south western Australia, and Aphanopetalum resinosum, endemic to southern Queensland and New South Wales.Until recently, these plants...
(1), Tetracarpaeaceae (1),
PenthoraceaePenthoraceae is a flowering plant family of rhizome forming herbs native to eastern North America and Eastern and Southeastern Asia.-References:* in Stevens, P. F. ....
(1),
PterostemonaceaePterostemonaceae is a small family of shrubs native to tropical and subtropical Mexico. The family is recognized by scientists working with the Angiosperm Phylogeny Group but is placed in the Grossulariaceae by other taxonomic systems.-References:...
(1), and Grossulariaceae (1). Some authors do not recognize
Choristylis as a separate genus from
IteaItea may refer to:*Itea , a genus of plants that includes Itea virginica, the scientific name of Virginia Sweetspire.*places in Greece:**Itea, Evros, a village in the southeastern part of the Evros Prefecture...
. Similarly, some authors sink
Liquidambar and
SemiliquidambarSemiliquidambar is a genus of plants, most recently treated in family Altingiaceae, though previously often treated in Hamamelidaceae. Recent research suggests that it may not be a true genus, but that the species normally treated within it are hybrids of other species of Altingiaceae; the taxonomy...
into
AltingiaAltingia is a genus of 11 species of flowering plants in the family Altingiaceae, formerly often treated in the related family Hamamelidaceae. The genus is native to southeastern Asia, in Bhutan, Cambodia, southern China, India, Indonesia, Laos, Malaysia, Myanmar, Thailand, and Vietnam.They are...
. Thus Altingiaceae and Iteaceae are monogeneric in some classifications.
History
Within the Saxifragales is a suprafamilial group known as the Saxifragaceae alliance. It comprises four families: Pterostemonaceae, Iteaceae, Grossulariaceae, and Saxifragaceae. These have long been known to be related to each other, but the
circumscriptionIn taxonomy, circumscription is the definition of the limits of a taxonomic group of organisms. One goal of taxonomy is to achieve a stable circumscription for every taxonomic group. Achieving stability can range from simple or difficult....
of Saxifragaceae has changed dramatically. It is now a much smaller family than it had been. Crassulaceae and Tetracarpaeaceae have long been associated with Saxifragaceae.
Penthorum has usually been associated with Crassulaceae, but sometimes with Saxifragaceae.
Two members of the core Saxifragales had sometimes been placed near Saxifragaceae, but usually elsewhere.
AphanopetalumAphanopetalum is a genus of twining shrubs or vines which are endemic to Australia.The genus is placed alone in family Aphanopetalaceae, which is in turn now placed in order Saxifragales...
was often placed in
CunoniaceaeThe Cunoniaceae is a family of 26 genera and about 350 species of woody plants in the Antarctic flora, native to Australia, New Caledonia, New Guinea, New Zealand, southern South America, the Mascarene Islands and southern Africa. Several of the genera have remarkable disjunct ranges, found on more...
, a family in
OxalidalesThe Oxalidales are an order of flowering plants, included within the rosid subgroup of dicotyledons. The following families are typically placed here:* Family Brunelliaceae* Family Cephalotaceae * Family Connaraceae...
, even though there were good reasons to put it in Saxifragales.
Aphanopetalum is now excluded from Cunoniaceae. Haloragaceae was often thought to be a family in
MyrtalesThe Myrtales are an order of flowering plants placed as a basal group within the rosid group of dicotyledons...
, but it is no longer included in that order.
Cercidiphyllaceae had for a long time been associated with Hamamelidaceae and
TrochodendraceaeTrochodendraceae is the botanical name for a family of flowering plants.The APG II system, of 2003 , also recognizes this family: it is unplaced as to order and left among the basal lineages of the eudicots...
and was often thought to be closer to the latter. Cercidiphyllaceae is now known to be a member of the woody
cladeA clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.[The term "monophyletic group" is used in this article...]
of Saxifragales, along with Hamamelidaceae, Altingiaceae, and Daphniphyllaceae, but Trochodendraceae is in the basal eudicot order
TrochodendralesTrochodendrales is a botanical name for an order of flowering plants. An order by this name was recognised in the Cronquist system, as comprising the families Tetracentraceae and Trochodendraceae, each consisting of a single species...
. Altingiaceae was usually not separated from Hamamelidaceae until phylogenetic studies showed that its inclusion might make Hamamelidaceae
paraphyleticIn phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all the descendants of that ancestor.- Relation to monophyletic groups :...
. The recognition of Altingiaceae as a separate family received strong statistical support in 2008.
Daphniphyllum was always thought to have an anomalous combination of characters and it was placed in several different orders before molecular phylogenetic analysis showed it to belong to Saxifragales.
Paeoniaceae possesses many
uniqueIn cladistics, an autapomorphy is a derived trait that is unique to a given terminal group. That is, it is found only in one member of a clade, but not found in any others or outgroup taxa, not even those most closely related to the group .An autapomorphy is not present in the closest relative of...
features and its taxonomic position was for a long time controversial. The idea has long persisted that
PaeoniaPeony or paeony is a name for plants in the genus Paeonia, the only genus in the flowering plant family Paeoniaceae. They are native to Asia, southern Europe and western North America. Boundaries between species are not clear and estimates of the number of species range from 25 to 40...
belongs in
RanunculalesRanunculales is an order of flowering plants. Of necessity it contains the family Ranunculaceae, the buttercup family.The APG system and the APG II system both recognize the order and place it among the basal eudicots, not assigned to a further clade...
, close to
GlaucidiumGlaucidium may refer to:* Glaucidium , the genus of pygmy owls.* Glaucidium , a genus of plants in the family Ranunculaceae....
. Paeoniaceae has been shown unequivocally to belong in Saxifragales, while
Glaucidium is in the family
RanunculaceaeRanunculaceae is a family of flowering plants also known as the "buttercup family" or "crowfoot family". The family name is derived from the genus Ranunculus. Members include Anemone , Ranunculus , Aconitum , and Clematis...
.
The family Peridiscaceae underwent radical shifting and recircumscription from 2003 to 2009. Originally, it consisted of two closely related genera,
Peridiscus and
Whittonia. The APG II system placed the family in
MalpighialesMalpighiales is one of the largest orders of flowering plants, containing about 16000 species, approximately 7.8% of the eudicots. The order is very diverse and hard to recognize except with molecular phylogenetic evidence. It is not part of any of the classification systems that are based only...
, based on a
DNA sequenceA DNA sequence or genetic sequence is a succession of letters representing the primary structure of a real or hypothetical DNA molecule or strand, with the capacity to carry information as described by the central dogma of molecular biology....
for the
rbcLRibulose-1,5-bisphosphate carboxylase oxygenase, most commonly known by the shorter name RuBisCO, is an enzyme that is used in the Calvin cycle to catalyze the first major step of carbon fixation, a process by which the atoms of atmospheric carbon dioxide are made available to organisms in the...
geneA gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring...
from
Whittonia. This sequence turned out to be not from
Whittonia, but from other plants whose
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
had contaminated the sample. After Peridiscaceae was finally placed in Saxifragales, it was expanded to include
SoyauxiaSoyauxia is a genus of flowering plants in the family Peridiscaceae. They are small trees or erect shrubs from wet forests of tropical West Africa. Eight species names have been published in Soyauxia. Additional species have been discovered, but their names and descriptions will not be...
in 2007, and expanded again to include
Medusandra in 2009.
Phylogeny
The phylogeny shown below is based on the one published by Shuguang Jian and coauthors in 2008. All branches have 100%
maximum likelihoodMaximum likelihood estimation is a popular statistical method used for fitting a statistical model to data, and providing estimates for the model's parameters....
bootstrap supportIn statistics, bootstrapping is a modern, computer-intensive, general purpose approach to statistical inference, falling within a broader class of resampling methods....
except where labeled with bootstrap percentage. Monogeneric families are represented by genus names.
External links