Rosids
Encyclopedia
The rosids are members of a large clade
of flowering plant
s, 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
. The rosids and the asterids
are by far the largest clades in the eudicots
.
Fossil rosids are known from the Cretaceous
period. Molecular clock
estimates indicate that the rosids originated in the Aptian
or Albian
stages of the Cretaceous, between 125 and 99.6 million years ago.
showed that the correct basis for the name "Rosidae" is a description of a group
of plants published in 1830 by Friedrich Gottlieb Bartling
. This clade was later renamed "Rosidae" and has been variously delimited
by different authors. The name "rosids" is informal, and not assumed to have any particular taxonomic rank
like the names authorized by the ICBN. The rosids are monophyletic based upon evidence found by molecular phylogenetic analysis.
Three different definitions
of the rosids are currently in use. Some authors include the orders Saxifragales
and Vitales in the rosids. Others exclude both of these orders. The circumscription used in this article is that of the APG II classification, which includes Vitales, but excludes Saxifragales.
), the others being Berberidopsidales
, Caryophyllales
, Dilleniales
, Santalales
, and the asterids
. Almost nothing is known about the relationships between these groups.
The eurosids, in turn are divided into seven groups: Fabidae, Geraniales
, Myrtales
, Crossosomatales
, Picramniales, Malvidae, and the unplaced family Apodanthaceae
. The Fabidae are often called the fabids, or eurosids I. Likewise, the Malvidae are often called the malvids, or eurosids II.
(not in any order). In addition to Vitales, Geraniales, Myrtales, Crossosomatales, and Picramniales, there are 8 orders in Fabidae and 4 orders in Malvidae. In 2009, Hengchang Wang and co-authors proposed that Malvidae be expanded to include Geraniales, Myrtales, Crossosomatales, and Picramniales. This larger circumscription of Malvidae received strong statistical support (100% bootstrap percentage
) in their analysis. Some of the orders have only recently been recognized. These are Vitales, Zygophyllales, Crossosomatales, Picramniales, and Huerteales.
and Huaceae
are included in the rosids, but not placed in any of its orders.
Apodanthaceae is an enigmatic family of achlorophyllous
parasites. They have been provisionally placed in Cucurbitales
by some, but their affinities remain obscure. The chloroplast genes that have been used to infer plant phylogeny do not provide much phylogenetic information for plants that lack chlorophyll, because in this case, these genes are nonfunctional pseudogene
s.
The family Huaceae is a member of the COM (Celastrales, Oxalidales, Malpighiales) clade of Fabidae. The question about Huaceae is whether it should be included in one of the COM orders or in an order by itself as a 4th member of the COM clade. Two studies have indicated that it should be placed in Oxalidales
, while one has indicated that it should not.
The nitrogen-fixing clade contains a high number of actinorhizal plant
s (which have root nodules containing nitrogen fixing bacteria, helping the plant grow in poor soils). Not all plants in this clade are actinorhizal, however.
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 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, containing about 70,000 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, more than a quarter of all angiosperms. The clade is divided into 16 to 20 orders
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...
, depending upon circumscription
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....
and classification
Biological classification
Biological classification, or scientific classification in biology, is a method to group and categorize organisms by biological type, such as genus or species. Biological classification is part of scientific taxonomy....
. These orders, in turn, together comprise about 140 families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
. The rosids and the 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...
are by far the largest clades in the eudicots
Eudicots
Eudicots and Eudicotyledons are botanical terms introduced by Doyle & Hotton to refer to a monophyletic group of flowering plants that had been called tricolpates or non-Magnoliid dicots by previous authors...
.
Fossil rosids are known from the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
period. Molecular clock
Molecular clock
The molecular clock is a technique in molecular evolution that uses fossil constraints and rates of molecular change to deduce the time in geologic history when two species or other taxa diverged. It is used to estimate the time of occurrence of events called speciation or radiation...
estimates indicate that the rosids originated in the Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
or Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
stages of the Cretaceous, between 125 and 99.6 million years ago.
The name
The name "rosids" is based upon the name "Rosidae", which had usually been understood to be a subclass. In 1967, Armen TakhtajanArmen Takhtajan
Armen Leonovich Takhtajan or Takhtajian , was a Soviet-Armenian botanist, one of the most important figures in 20th century plant evolution and systematics and biogeography. His other interests included morphology of flowering plants, paleobotany, and the flora of the Caucasus...
showed that the correct basis for the name "Rosidae" is a description of a group
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
of plants published in 1830 by Friedrich Gottlieb Bartling
Friedrich Gottlieb Bartling
Friedrich Gottlieb Bartling was a German botanist who was a native of Hanover.He studied natural sciences at the University of Göttingen, and in 1818 took a botanical journey through Hungary and Croatia. In 1822 he became a lecturer at Göttingen, where he later became a professor, and in 1837 was...
. This clade was later renamed "Rosidae" and has been variously delimited
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....
by different authors. The name "rosids" is informal, and not assumed 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...
like the names authorized by the ICBN. The rosids are monophyletic based upon evidence found by molecular phylogenetic analysis.
Three different definitions
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 the rosids are currently in use. Some authors include the orders Saxifragales
Saxifragales
Saxifragales is an order of flowering plants. 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...
and Vitales in the rosids. Others exclude both of these orders. The circumscription used in this article is that of the APG II classification, which includes Vitales, but excludes Saxifragales.
Relationships
The rosids and Saxifragales form a clade. This is one of 6 groups that compose the Pentapetalae (core eudicots minus GunneralesGunnerales
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,...
), the others being 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:...
, Dilleniales
Dilleniales
Dilleniales is an order of flowering plants. The Cronquist system, of 1981, recognized such order and placed it in subclass Dilleniidae. It used the following circumscription:*order Dilleniales*: family Dilleniaceae*: family Paeoniaceae...
, 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...
, and the 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...
. Almost nothing is known about the relationships between these groups.
Classification
The rosids consist of two groups: the order Vitales and the eurosids (true rosids).The eurosids, in turn are divided into seven groups: Fabidae, Geraniales
Geraniales
Geraniales are a small order of flowering plants, included within the rosid subgroup of dicotyledons. The largest family in the order is Geraniaceae with over 800 species. In addition, the order includes some small families, contributing together another less than 40 species...
, Myrtales
Myrtales
The Myrtales are an order of flowering plants placed as a basal group within the rosid group of dicotyledons...
, Crossosomatales
Crossosomatales
The Crossosomatales are an order, newly recognized by the AGP II, of flowering plants, included within the Rosids, which are part of the eudicots...
, Picramniales, Malvidae, and the unplaced family Apodanthaceae
Apodanthaceae
The family Apodanthaceae comprises 22 to 30 species of endoparasitic herbs. They live in branches or roots of their host , emerging only to flower. The only leaves present are several bracts at the base of each flower. The plants do not carry out any photosynthesis...
. The Fabidae are often called the fabids, or eurosids I. Likewise, the Malvidae are often called the malvids, or eurosids II.
Orders
The rosids consist of 17 orders and 2 families that are placed incertae sedisIncertae sedis
, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
(not in any order). In addition to Vitales, Geraniales, Myrtales, Crossosomatales, and Picramniales, there are 8 orders in Fabidae and 4 orders in Malvidae. In 2009, Hengchang Wang and co-authors proposed that Malvidae be expanded to include Geraniales, Myrtales, Crossosomatales, and Picramniales. This larger circumscription of Malvidae received strong statistical support (100% bootstrap percentage
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...
) in their analysis. Some of the orders have only recently been recognized. These are Vitales, Zygophyllales, Crossosomatales, Picramniales, and Huerteales.
Unplaced families
The families ApodanthaceaeApodanthaceae
The family Apodanthaceae comprises 22 to 30 species of endoparasitic herbs. They live in branches or roots of their host , emerging only to flower. The only leaves present are several bracts at the base of each flower. The plants do not carry out any photosynthesis...
and Huaceae
Huaceae
Huaceae is a family of plant in the rosids group, which has been classed in the orders Malpighiales, Malvales, and Violales or in its own order Huales. The APG II system places it in the clade eurosids I, whereas the APG III system of 2009 placed it within the Oxalidales. It contains the following...
are included in the rosids, but not placed in any of its orders.
Apodanthaceae is an enigmatic family of achlorophyllous
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
parasites. They have been provisionally placed in Cucurbitales
Cucurbitales
The Cucurbitales are an order of flowering plants, included in the rosid group of dicotyledons. This order mostly belongs to tropical areas, with limited presence in subtropic and temperate regions. The order includes shrubs and trees, together with many herbs and climbers...
by some, but their affinities remain obscure. The chloroplast genes that have been used to infer plant phylogeny do not provide much phylogenetic information for plants that lack chlorophyll, because in this case, these genes are nonfunctional pseudogene
Pseudogene
Pseudogenes are dysfunctional relatives of known genes that have lost their protein-coding ability or are otherwise no longer expressed in the cell...
s.
The family Huaceae is a member of the COM (Celastrales, Oxalidales, Malpighiales) clade of Fabidae. The question about Huaceae is whether it should be included in one of the COM orders or in an order by itself as a 4th member of the COM clade. Two studies have indicated that it should be placed 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...
, while one has indicated that it should not.
Phylogeny
The phylogeny shown below is adapted from Wang and co-authors (2009), with order names from the Angiosperm Phylogeny Website. Branches with less than 50% bootstrap support are collapsed. Other branches have 100% bootstrap support except where shown.The nitrogen-fixing clade contains a high number of actinorhizal plant
Actinorhizal plant
Actinorhizal plants are a group of angiosperms characterized by their ability to form a symbiosis with the nitrogen fixing actinobacteria Frankia...
s (which have root nodules containing nitrogen fixing bacteria, helping the plant grow in poor soils). Not all plants in this clade are actinorhizal, however.