Saxifragales
Encyclopedia
Saxifragales is an order
of flowering plant
s. Their closest relatives are a large eudicot group known as the rosids
by the definition
of rosids given in the APG II classification system
. Some authors define the rosids more widely, including Saxifragales as their most basal
group. Saxifragales is one of the eight groups that compose the core eudicots. The others are Gunnerales
, Dilleniaceae
, rosids
, Santalales
, Berberidopsidales
, Caryophyllales
, and asterids
.
Saxifragales has an extensive fossil
record. The extant members are apparently remnants of a formerly diverse
and widespread
order.
Saxifragales, as it is now understood, is based upon the results of molecular phylogenetic studies of DNA sequence
s. It is not part of any of the classification systems
based on plant morphology
. The group is much in need of comparative anatomical
study
, especially in light of the recent expansion of the family Peridiscaceae
to include Medusandra, a genus that before 2009, had usually not been placed in Saxifragales.
The order is divided into suprafamilial
groups as shown on the phylogenetic tree
below. These groups are informal and are not understood to have any particular taxonomic rank
.
sensu lato is recognized as a family consisting of Haloragaceae sensu stricto, Penthorum
, Tetracarpaea
, and Aphanopetalum
. About 95% of the species are in five families: Crassulaceae
(1400), Saxifragaceae
(500), Grossulariaceae (150 - 200), Haloragaceae
(150), and Hamamelidaceae
(100). Most of the families are monogeneric. The number of genera in each family is as follows:
Some authors do not recognize Choristylis as a separate genus from Itea
. Similarly, some authors sink Liquidambar and Semiliquidambar
into Altingia
. Thus Altingiaceae and Iteaceae are monogeneric in some classifications.
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. Aphanopetalum
was often placed in Cunoniaceae
, a family in Oxalidales
, 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 Myrtales
, but it is no longer included in that order.
Cercidiphyllaceae had for a long time been associated with Hamamelidaceae and Trochodendraceae
and was often thought to be closer to the latter. Cercidiphyllaceae is now known to be a member of the woody clade
of Saxifragales, along with Hamamelidaceae, Altingiaceae, and Daphniphyllaceae, but Trochodendraceae is in the basal eudicot order Trochodendrales. Altingiaceae was usually not separated from Hamamelidaceae until phylogenetic studies showed that its inclusion might make Hamamelidaceae paraphyletic
. 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 unique
features and its taxonomic position was for a long time controversial. The idea has long persisted that Paeonia
belongs in Ranunculales
, close to Glaucidium
. Paeoniaceae has been shown unequivocally to belong in Saxifragales, while Glaucidium is in the family Ranunculaceae
.
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 Malpighiales
, based on a DNA sequence
for the rbcL
gene
from Whittonia. This sequence turned out to be not from Whittonia, but from other plants whose DNA
had contaminated the sample. After Peridiscaceae was finally placed in Saxifragales, it was expanded to include Soyauxia
in 2007, and expanded again to include Medusandra in 2009.
bootstrap support
except where labeled with bootstrap percentage. Monogeneric families are represented by genus names.
Order (biology)
In 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 plant
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
s. Their closest relatives are a large eudicot group known as the rosids
Rosids
The rosids are members of a large clade of flowering plants, containing about 70,000 species, more than a quarter of all angiosperms. The clade is divided into 16 to 20 orders, depending upon circumscription and classification. These orders, in turn, together comprise about 140 families...
by the definition
Circumscription (taxonomy)
In 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 be simple or difficult....
of rosids given in the APG II classification system
History of plant systematics
The 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 basal
Basal (phylogenetics)
In 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 Gunnerales
Gunnerales
Gunnerales is an order of flowering plants. In the APG III system it contains two genera: Gunnera and Myrothamnus. These are assigned to two separate families . In the Cronquist system Gunneraceae was placed in the Haloragales and Myrothamnaceae in the Hamamelidales.-External links:* in Stevens,...
, Dilleniaceae
Dilleniaceae
Dilleniaceae 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....
, rosids
Rosids
The rosids are members of a large clade of flowering plants, containing about 70,000 species, more than a quarter of all angiosperms. The clade is divided into 16 to 20 orders, depending upon circumscription and classification. These orders, in turn, together comprise about 140 families...
, Santalales
Santalales
Santalales 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...
, Berberidopsidales
Berberidopsidales
Berberidopsidales 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...
, Caryophyllales
Caryophyllales
Caryophyllales is an order of flowering plants that includes the cacti, carnations, amaranths, ice plants, and many carnivorous plants. Many members are succulent, having fleshy stems or leaves.-Description:...
, and asterids
Asterids
In 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 fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
record. The extant members are apparently remnants of a formerly diverse
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
and widespread
Cosmopolitan distribution
In biogeography, a taxon is said to have a cosmopolitan distribution if its range extends across all or most of the world in appropriate habitats. For instance, the killer whale has a cosmopolitan distribution, extending over most of the world's oceans. Other examples include humans, the lichen...
order.
Saxifragales, as it is now understood, is based upon the results of molecular phylogenetic studies of DNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
s. It is not part of any of the classification systems
Systematics
Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...
based on plant morphology
Plant morphology
Plant morphology or phytomorphology is the study of the physical form and external structure 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 anatomical
Comparative anatomy
Comparative anatomy is the study of similarities and differences in the anatomy of organisms. It is closely related to evolutionary biology and phylogeny .-Description:...
study
Research
Research can be defined as the scientific search for knowledge, or as any systematic investigation, to establish novel facts, solve new or existing problems, prove new ideas, or develop new theories, usually using a scientific method...
, especially in light of the recent expansion of the family Peridiscaceae
Peridiscaceae
Peridiscaceae 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 Soyauxia...
to include Medusandra, a genus that before 2009, had usually not been placed in Saxifragales.
The order is divided into suprafamilial
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
groups as shown on the phylogenetic tree
Phylogenetic tree
A phylogenetic tree or evolutionary tree is a branching diagram or "tree" showing the inferred evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical and/or genetic characteristics...
below. These groups are informal and are not understood to have any particular taxonomic rank
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
.
Families
Saxifragales contains about 2470 species. These are distributed into 15 families, or into 12 families if HaloragaceaeHaloragaceae
Haloragaceae is a dicotyledon flowering plant family in the order Saxifragales, based on the phylogenetic APG III system. In the Cronquist system, it was included in the order Haloragales.- Distribution :...
sensu lato is recognized as a family consisting of Haloragaceae sensu stricto, Penthorum
Penthorum
Penthorum 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
Tetracarpaea
Tetracarpaea is the only genus in the flowering plant family Tetracarpaeaceae. Some taxonomists place it in the family Haloragaceae sensu lato, expanding that family from its traditional circumscription to include Penthorum and Tetracarpaea, and sometimes Aphanopetalum as well.Tetracarpaea has one...
, and Aphanopetalum
Aphanopetalum
Aphanopetalum is a genus of twining shrubs or vines in the family Aphanopetalaceae 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: Crassulaceae
Crassulaceae
Crassulaceae, or the orpine family, are 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), Saxifragaceae
Saxifragaceae
Saxifragaceae is a plant family with about 460 known species in 36 genera. In Europe there are 12 genera.The flowers are hermaphroditic and actinomorphic...
(500), Grossulariaceae (150 - 200), Haloragaceae
Haloragaceae
Haloragaceae is a dicotyledon flowering plant family in the order Saxifragales, based on the phylogenetic APG III system. In the Cronquist system, it was included in the order Haloragales.- Distribution :...
(150), and Hamamelidaceae
Hamamelidaceae
The 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:
- CrassulaceaeCrassulaceaeCrassulaceae, or the orpine family, are 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), - SaxifragaceaeSaxifragaceaeSaxifragaceae is a plant family with about 460 known species in 36 genera. In Europe there are 12 genera.The flowers are hermaphroditic and actinomorphic...
(33), - HamamelidaceaeHamamelidaceaeThe 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), - HaloragaceaeHaloragaceaeHaloragaceae is a dicotyledon flowering plant family in the order Saxifragales, based on the phylogenetic APG III system. In the Cronquist system, it was included in the order Haloragales.- Distribution :...
(8), - PeridiscaceaePeridiscaceaePeridiscaceae 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 Soyauxia...
(4), - AltingiaceaeAltingiaceaeAltingiaceae, a small family of flowering plants in the order Saxifragales, 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, the...
(3), - IteaceaeIteaceaeIteaceae is a flowering plant family of trees and shrubs native to the eastern USA, south eastern Africa, and south and Southeastern Asia. Some older taxonomic systems place the genera in this family in the Grossulariaceae. The APG III system of 2009 includes the former Pterostemonaceae in Iteaceae...
(2), - Paeoniaceae (1),
- Cercidiphyllaceae (1),
- Daphniphyllaceae (1),
- Aphanopetalaceae (1),
- Tetracarpaeaceae (1),
- PenthoraceaePenthoraceaePenthoraceae 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), - PterostemonaceaePterostemonaceaePterostemonaceae Small is a small family of shrubs native to tropical and subtropical Mexico. The family was recognized by scientists working with the Angiosperm Phylogeny Group but is placed in the Grossulariaceae by other taxonomic systems...
(1), and - Grossulariaceae (1).
Some authors do not recognize Choristylis as a separate genus from Itea
Itea (plant)
Itea is a genus of about 10 species of shrubs and small trees. The leaves are alternate. Flowers are small, with 5 sepals and 5 petals, borne in racemes or spikes....
. Similarly, some authors sink Liquidambar and Semiliquidambar
Semiliquidambar
Semiliquidambar 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 Altingia
Altingia
Altingia 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...
. 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 circumscriptionCircumscription (taxonomy)
In 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 be 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. Aphanopetalum
Aphanopetalum
Aphanopetalum is a genus of twining shrubs or vines in the family Aphanopetalaceae 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 Cunoniaceae
Cunoniaceae
The Cunoniaceae is a family of 26 genera and about 350 species of woody plants in the Antarctic flora, with many laurifolia species with glossy leaves endemic to laurel forest habitat. The family is native to Australia, New Caledonia, New Guinea, New Zealand, southern South America, the Mascarene...
, a family in Oxalidales
Oxalidales
The Oxalidales are an order of flowering plants, included within the rosid subgroup of eudicots. 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 Myrtales
Myrtales
The 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 Trochodendraceae
Trochodendraceae
Trochodendraceae is a family of flowering plants with two living genera found in southeast Asia. The two living species share the feature of secondary xylem without vessels, which is quite rare in angiosperms...
and was often thought to be closer to the latter. Cercidiphyllaceae is now known to be a member of the woody clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
of Saxifragales, along with Hamamelidaceae, Altingiaceae, and Daphniphyllaceae, but Trochodendraceae is in the basal eudicot order Trochodendrales. Altingiaceae was usually not separated from Hamamelidaceae until phylogenetic studies showed that its inclusion might make Hamamelidaceae paraphyletic
Paraphyly
A group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
. 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 unique
Autapomorphy
In cladistics, an autapomorphy is a distinctive anatomical feature, known as 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...
features and its taxonomic position was for a long time controversial. The idea has long persisted that Paeonia
Peony
Peony 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...
belongs in Ranunculales
Ranunculales
Ranunculales is an order of flowering plants. Of necessity it contains the family Ranunculaceae, the buttercup family, because the name of the order is based on the name of a genus in that family. Ranunculales belongs to a paraphyletic group known as the basal eudicots...
, close to Glaucidium
Glaucidium (plant)
Glaucidium is a genus of plants in family Ranunculaceae, comprising a single species Glaucidium palmatum...
. Paeoniaceae has been shown unequivocally to belong in Saxifragales, while Glaucidium is in the family Ranunculaceae
Ranunculaceae
Ranunculaceae are a family of about 1700 species of flowering plants in about 60 genera, distributed worldwide....
.
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 Malpighiales
Malpighiales
Malpighiales 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 on...
, based on a DNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
for the rbcL
RuBisCO
Ribulose-1,5-bisphosphate carboxylase oxygenase, commonly known by the shorter name RuBisCO, is an enzyme involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is converted by plants to energy-rich molecules such as glucose. RuBisCo is an abbreviation...
gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
from Whittonia. This sequence turned out to be not from Whittonia, but from other plants whose DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
had contaminated the sample. After Peridiscaceae was finally placed in Saxifragales, it was expanded to include Soyauxia
Soyauxia
Soyauxia 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 specific names have been published in Soyauxia. Additional species have been discovered, but their names and descriptions will not be published...
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
In statistics, maximum-likelihood estimation is a method of estimating the parameters of a statistical model. When applied to a data set and given a statistical model, maximum-likelihood estimation provides estimates for the model's parameters....
bootstrap support
Bootstrapping (statistics)
In statistics, bootstrapping is a computer-based method for assigning measures of accuracy to sample estimates . This technique allows estimation of the sample distribution of almost any statistic using only very simple methods...
except where labeled with bootstrap percentage. Monogeneric families are represented by genus names.
External links
- plant order classification at: Saxifragales
- Trees At: Angiosperm Phylogeny Website At: Missoure Botanical Garden Website
- Saxifragales At: Angiosperm Phylogeny Website
- Wurdack and Davis on Malpighiales PMID 21628300
- Shuguang Jian et alii on phylogeny of Saxifragales PMID 18275001