The APG III system of flowering plant classification is the third version of a modern, mostly molecular-based, system of plant taxonomy being developed by the Angiosperm Phylogeny Group (APG). Published in 2009, it was superseded in 2016 by a further revision, the APG IV system.
Along with the publication outlining the new system, there were two accompanying publications in the same issue of the Botanical Journal of the Linnean Society. The first, by Chase & Reveal, was a formal phylogenetic classification of all land plants (embryophytes), compatible with the APG III classification. As the APG have chosen to eschew ranks above order, this paper was meant to fit the system into the existing Linnaean hierarchy for those that prefer such a classification. The result was that all land plants were placed in the class Equisetopsida, which was then divided into 16 subclasses and a multitude of superorders. The second, by Haston et al., was a linear sequence of families following the APG III system (LAPG III).
This provided a numbered list to the 413 families of APG III. A linear sequence is of particular use to herbarium curators and those working on floristic works wishing to arrange their taxa according to APG III.
The APG III system recognized all of the 45 orders of the previous system, as well as 14 new ones. The order Ceratophyllales was erroneously marked as a new order, as it had been recognized in both of the previous APG systems. The newly recognized orders were:
The designation of alternative "bracketed families" was abandoned in APG III, because its inclusion in the previous system had been unpopular. APG III recognized 413 families, 43 fewer than in the previous system. Forty-four of the 55 "bracketed families" were discontinued, and 20 other families were discontinued as well.
The discontinued bracketed families were:
The other discontinued families were:
21 families were accepted in the APG III system which had not been in the previous system, and a few families were moved to a different position. The newly recognized families are:
The number of families not placed in any order was reduced from 39 to 10. Apodanthaceae and Cynomoriaceae were placed among the angiosperms, incertae sedis, that is, not in any group within the angiosperms. Eight other families were placed incertae sedis in various supra-ordinal groups within the angiosperms. The families not placed in any order were:
The paragraph below shows the number of families in each order and the placement of those families that were not included in any order. These figures were produced by simply counting the families in the text of the paper that established APG III.
ORDERS: Amborellales (1), Nymphaeales (3), Austrobaileyales (3), Chloranthales (1), Canellales (2), Piperales (5), Magnoliales (6), Laurales (7), Acorales (1), Alismatales (13), Petrosaviales (1), Dioscoreales (3), Pandanales (5), Liliales (10), Asparagales (14), Arecales (1), Poales (16), Commelinales (5), Zingiberales (8), Ceratophyllales (1), Ranunculales (7), Proteales (3), Trochodendrales (1), Buxales (2), Gunnerales (2), Saxifragales (14), Vitales (1), Zygophyllales (2), Celastrales (2), Oxalidales (7), Malpighiales (35), Fabales (4), Rosales (9), Fagales (7), Cucurbitales (7), Geraniales (3), Myrtales (9), Crossosomatales (7), Picramniales (1), Sapindales (9), Huerteales (3), Brassicales (17), Malvales (10), Berberidopsidales (2), Santalales (7), Caryophyllales (34), Cornales (6), Ericales (22), Garryales (2), Gentianales (5), Solanales (5), Lamiales (23), Aquifoliales (5), Asterales (11), Escalloniales (1), Bruniales (2), Apiales (7), Paracryphiales (1), Dipsacales (2).
SUPRA-ORDINAL GROUPS: commelinids (1), basal eudicots (1), Pentapetalae (1), lamiids incertae sedis (3), core lamiids (2), angiosperms incertae sedis (2).
The circumscription of the family Icacinaceae remains especially doubtful. Apodytes and its close relative, Rhaphiostylis, as well as Emmotum, Cassinopsis, and a few other genera were provisionally retained within it until further studies can determine whether they properly belong there.
Three genera (Gumillea, Nicobariodendron, and Petenaea) were placed within the angiosperms incertae sedis. Gumillea had been unplaced in APG II. Nicobariodendron and Petenaea were newly added to the list. The latter was later placed into its own family Petenaeaceae in the order Huerteales
The classification is shown below in two versions. The short version goes to the level of orders and of families unplaced in an order. The detailed version shows all the families. Orders at the same level in the classification are arranged alphabetically. Note that orders may not contain the same families as in earlier versions of the APG system (APG system, APG II system). Further detail on relationships can be seen in the phylogenetic tree below.
* = new family placement;
† = newly recognized order for the APG system;
§ = new family circumscription described in the text;
$ = families that represent the broader circumscription of options available in APG II and favoured here;
$$ = families that were in square brackets in APG II, the narrower circumscriptions favoured here.
The APG III system was based on a phylogenetic tree for the angiosperms which included all of the 59 orders and 4 of the unplaced families. The systematic positions of the other 6 unplaced families was so uncertain that they could not be placed in any of the polytomies in the tree. They are shown in the classification table entitled "Detailed version" above, 4 in Euasterids I and 2 in Taxa of uncertain position.
The phylogenetic tree shown below was published with the APG III system, but without some of the labels that are added here.
A number of subfamilies have been proposed to replace some of the families which were optional (i.e. bracketed) in APG II, but have been discontinued in APG III. These are shown in the table below.
|APG II bracketed family||APG III family: subfamily|
Note: This is a selected list of the more influential systems. There are many other systems, for instance a review of earlier systems, published by Lindley in his 1853 edition, and Dahlgren (1982). Examples include the works of Scopoli, Batsch and Grisebach.Apiales
The Apiales are an order of flowering plants. The families are those recognized in the APG III system. This is typical of the newer classifications, though there is some slight variation and in particular, the Torriceliaceae may be divided.Under this definition, well-known members include carrots, celery, parsley, and Hedera helix (English ivy).
The order Apiales is placed within the asterid group of eudicots as circumscribed by the APG III system. Within the asterids, Apiales belongs to an unranked group called the campanulids, and within the campanulids, it belongs to a clade known in phylogenetic nomenclature as Apiidae. In 2010, a subclade of Apiidae named Dipsapiidae was defined to consist of the three orders: Apiales, Paracryphiales, and Dipsacales.Berberidopsidales
Berberidopsidales is an order of Southern Hemisphere woody flowering plants. The name is newly accepted in the APG III system of plant taxonomy. APG II system, of 2003, mentions the possibility of recognizing the order, as comprising the families Berberidopsidaceae and Aextoxicaceae. However, APG II left the families unplaced as to order, assigning them to the clade core eudicots. The APG III system of 2009 formally recognized the order.The family Aextoxicaceae is a monotypic family native to Chile; Berberidopsidaceae is a family of 2 genera and 3 species native to Chile and eastern Australia.Boraginales
Boraginales is a valid taxonomic name at the rank of order for a group of flowering plants. When recognized, it includes Boraginaceae and closely related asterid families.
Boraginales is recognized in neither of two major classification systems, the Cronquist system and the APG III system, but has been recognized in some recent scientific papers. The circumscription of Boraginales is essentially identical to the circumscription of Boraginaceae sensu APG. The APG III system takes a broad view of Boraginaceae, including within it the traditionally recognized families Hydrophyllaceae and Lennoaceae based on recent molecular phylogenies that show that Boraginaceae, as traditionally defined, is paraphyletic over these two families. APG III includes Boraginaceae in the Euasterid I (lamiid) clade but this family is otherwise unplaced; its precise relationship to other families in the Euasterid I group remains unclear. In a phylogenetic study of DNA sequences of selected genes, Boraginales was resolved as sister to Lamiales sensu APG, but that result had only 65% maximum likelihood bootstrap support.In the 2016 APG IV system Boraginales is an order with only one family Boraginaceae, which includes the former family Codonaceae.In the Cronquist system, Boraginaceae (including Cordiaceae, Ehretiaceae, and Heliotropiaceae) and Lennoaceae were placed in Lamiales, and Hydrophyllaceae in Solanales.
In some recent publications, Boraginaceae sensu APG has been recognized at the rank of order as Boraginales. As such, it has been split into several families: Boraginaceae s.s., Cordiaceae, Ehretiaceae, Heliotropiaceae, and Hydrophyllaceae. Some authors have defined a Boraginaceae sensu strictissimo by recognizing Codonaceae and Wellstediaceae as monogeneric families separate from Boraginaceae sensu stricto. Boraginaceae is hard to characterize morphologically if it includes the genera Codon and Wellstedia. Codon was long regarded as an unusual member of Hydrophyllaceae, but in 1998, a molecular phylogenetic study showed that it is closer to Boraginaceae.The achlorophyllous holoparasites Lennoa and Pholisma were once regarded as a family, Lennoaceae, but it is now known that they form a clade that is nested within Ehretiaceae. Some studies have indicated that Hydrophyllaceae is paraphyletic if the tribe Nameae is included within it, but further studies will be needed to resolve this issue.The inclusion of the genus Hoplestigma in Boraginales was occasionally doubted until it was strongly confirmed in a cladistic study in 2014. Hoplestigma is the closest relative of Cordiaceae and it has been recommended that the latter be expanded to include it.
Hydrolea was thought to belong in Hydrophyllaceae for more than a century after it was placed there by Asa Gray, but it is now known to belong in the order Solanales as sister to Sphenoclea.Pteleocarpa was long regarded as an anomaly, and was usually placed in Boraginales, but with considerable doubt. The molecular evidence strongly supports it as sister to Gelsemiaceae, and that family has been expanded to include it.Boraginoideae
Boraginoideae is a subfamily of the flowering plant family Boraginaceae, as that family is defined in the APG III system of classification for flowering plants. The Angiosperm Phylogeny Group has not actually specified subfamilies within Boraginaceae. Some taxonomists place the genera Codon and Wellstedia in Boraginoideae. Others place one or both of these in separate, monogeneric subfamilies. Codon was long regarded as an odd member of Hydrophylloideae, but in 1998, a molecular phylogenetic study showed that it is closer to Boraginoideae.Many of the botanists who work with Boraginaceae do not follow the APG III system. Instead, they recognize five to eight families in the order Boraginales.Comparisons of DNA sequences by cladistic methods have strongly supported the division of Boraginoideae into four tribes: Echiochileae, Boragineae, Lithospermeae, and Cynoglosseae.Calophyllaceae
Calophyllaceae is a family of flowering plants in the order Malpighiales and is recognized by the APG III system of classification. Most of the 14 genera and 475 species included in this family were previously recognized in the tribe Calophylleae of the Clusiaceae family. The Angiosperm Phylogeny Group determined that splitting this clade of genera off into their own family was necessary.Dilleniales
The Dilleniales are an order of flowering plants, potentially containing one family, Dilleniaceae. The APG III system of 2009, like the earlier APG II system of 2003, left the Dilleniaceae unplaced as to order, while noting that the name Dilleniales was available. Stevens at the Angiosperm Phylogeny Website has subsequently placed Dilleniaceae in the order Dilleniales.The Cronquist system, of 1981, recognized such an order and placed it in subclass Dilleniidae. It used the following circumscription:
family PaeoniaceaeThe Takhtajan system of 1969 had the families Dilleniaceae and Crossosomataceae in the order.The APG III system assigned the second of these families, the Paeoniaceae, to the order Saxifragales.Dipsacales
The Dipsacales are an order of flowering plants, included within the asterid group of dicotyledons. In the APG III system of 2009, the order includes only two families, Adoxaceae and a broadly defined Caprifoliaceae. Some well-known members of the Dipsacales order are honeysuckle, elder, viburnum, and valerian.
Under the Cronquist system, the order included Adoxaceae, Caprifoliaceae sensu stricto, Dipsacaceae, and Valerianaceae. Under the 2003 APG II system, the circumscription of the order was much the same but the system allowed either a broadly circumscribed Caprifoliaceae including the families Diervillaceae, Dipsacaceae, Linnaeaceae, Morinaceae, and Valerianaceae, or these families being kept separate. The APG III system only uses the broadly circumscribed Caprifoliceae.The Dipsacales appear to be most closely related to the Paracryphiales.Lomandroideae
Lomandroideae is a subfamily of monocot flowering plants in the family Asparagaceae, order Asparagales, according to the APG III system of 2009. The subfamily name is derived from the generic name of the type genus, Lomandra. The group has previously been treated as a separate family Laxmanniaceae. In the Kubitzki system, it is treated as Lomandraceae Lotsy.The subfamily consists of some 15 genera and about 180 species from Australasia, southeast Asia, the Americas and the Pacific Islands. The best-known genus is Cordyline.Melanthiaceae
Melanthiaceae is a family of flowering perennial herbs native to the Northern Hemisphere. Along with many other lilioid monocots, early authors considered members of this family to belong to the family Liliaceae, in part because both their sepals and petals closely resemble each other and are often large and showy like those of lilies, while some more recent taxonomists have placed them in a family Trilliaceae. The most authoritative modern treatment, however, the APG III system of 2009 (unchanged from the 2003 APG II system and the 1998 APG system), places the family in the order Liliales, in the clade monocots. Circumscribed in this way, the family includes up to 17 genera.
Familiar members of the family include Herb Paris (Paris quadrifolia) and the trilliums.Montiaceae
Montiaceae are a family of flowering plants, comprising about 14 genera with about 230 known species, ranging from herbaceous plants to shrubs. The family has a cosmopolitan distribution.
The family Montiaceae was newly adopted in the APG III system and includes members of the Caryophyllales formerly listed in Portulacaceae.Myrtales
The Myrtales are an order of flowering plants placed as a sister to the eurosids II clade as of the publishing of the Eucalyptus grandis genome in June 2014. The APG III system of classification for angiosperms still places it within the eurosids. The following families are included as of APG III:
Alzateaceae S. A. Graham
Combretaceae R. Br. (leadwood family)
Crypteroniaceae A. DC.
Lythraceae J. St.-Hil. (loosestrife and pomegranate family)
Melastomataceae Juss. (including Memecylaceae DC.)
Myrtaceae Juss. (myrtle family; including Heteropyxidaceae Engl. & Gilg, Psiloxylaceae Croizat)
Onagraceae Juss. (evening primrose and Fuchsia family)
Penaeaceae Sweet ex Guill. (including Oliniaceae Arn., Rhynchocalycaceae L. A. S. Johnson & B. G. Briggs)
Vochysiaceae A. St.-Hil.The Cronquist system gives essentially the same composition, except the Vochysiaceae are removed to the order Polygalales, and the Thymelaeaceae are included. The families Sonneratiaceae, Trapaceae, and Punicaceae are removed from the Lythraceae. In the classification system of Dahlgren the Myrtales were in the superorder Myrtiflorae (also called Myrtanae). The APG III system agrees with the older Cronquist circumscriptions of treating Psiloxylaceae and Heteropyxidaceae within Myrtaceae, and Memecyclaceae within Melastomataceae.
Ellagitannins are reported in dicotyledoneous angiospermes, and notably in species in the order Myrtales.Nartheciaceae
Nartheciaceae is a family of flowering plants. The APG III system places it in the order Dioscoreales, in the clade monocots. As circumscribed by APG IV (2016) it includes 35 species of herbaceous plants in the following five genera:
Nolinoideae is a monocot subfamily of the family Asparagaceae in the APG III system of 2009. It used to be treated as a separate family, Ruscaceae s.l. The family name is derived from the generic name of the type genus, Nolina.
The subfamily includes genera that had been placed in a range of different families, including Ruscaceae s.s., Nolinaceae, Dracaenaceae, Convallariaceae and Eriospermaceae. Like many groups of lilioid monocots, the genera included here were once included in a wide interpretation of the family Liliaceae.Pentaphylacaceae
The Pentaphylacacaeae are a small family of plants within the order Ericales. In the APG III system of 2009, it includes the former family Ternstroemiaceae.As of September 2014, the Angiosperm Phylogeny Website included these genera in the family:
Symplococarpon Airy Shaw
Rosales is an order of flowering plants. It is sister to a clade consisting of Fagales and Cucurbitales. It contains about 7700 species, distributed into about 260 genera. Rosales comprise nine families, the type family being the rose family, Rosaceae. The largest of these families are Rosaceae (90/2500) and Urticaceae (54/2600). The order Rosales is divided into three clades that have never been assigned a taxonomic rank. The basal clade consists of the family Rosaceae; another clade consists of four families, including Rhamnaceae; and the third clade consists of the four urticalean families.The order Rosales is strongly supported as monophyletic in phylogenetic analyses of DNA sequences, such as those carried out by members of the Angiosperm Phylogeny Group. In their APG III system of plant classification, they defined Rosales as consisting of the nine families listed in the box on the right. The relationships of these families were uncertain until 2011, when they were resolved in a molecular phylogenetic study based on two nuclear genes and ten chloroplast genes.Well-known members of Rosales include: roses, strawberries, blackberries and raspberries, apples and pears, plums, peaches and apricots, almonds, rowan and hawthorn, jujube, elms, banyans, figs, mulberries, breadfruit, nettles, hops, and cannabis.Sapindales
Sapindales is an order of flowering plants. Well-known members of Sapindales include citrus; maples, horse-chestnuts, lychees and rambutans; mangos and cashews; frankincense and myrrh; mahogany and neem.
The APG III system of 2009 includes it in the clade malvids (in rosids, in eudicots) with the following nine families:
Nitrariaceae (including Peganaceae and Tetradiclidaceae)
SimaroubaceaeThe APG II system of 2003 allowed the optional segregation of families now included in the Nitrariaceae.
In the classification system of Dahlgren the Rutaceae were placed in the order Rutales, in the superorder Rutiflorae (also called Rutanae). The Cronquist system of 1981 used a somewhat different circumscription, including the following families:
ZygophyllaceaeThe difference from the APG III system is not as large as may appear, as the plants in the families Aceraceae and Hippocastanaceae stay in this order at APG III (both included in family Sapindaceae). The species now composing the family Nitrariaceae in APG III also belonged to this order in the Cronquist system as part of the family Zygophyllaceae, while those now in the family Kirkiaceae were present as part of the family Simaroubaceae.Staphyleaceae
Staphyleaceae is a small family of flowering plants in the order Crossosomatales, native to the Northern Hemisphere and also in South America. The largest genus Staphylea, which gives the family its name, contains the "bladdernut" trees. The family includes two genera with ca 45 known species.
Excluded generaThese two genera, formerly placed here, are now included in the Tapisciaceae (Huerteales) as of the APG III system (2009).
Theaceae () is a family of flowering plants, composed of shrubs and trees, including the camellias. It can be described as having from seven to 40 genera, depending on the source and the method of circumscription used. The family Ternstroemiaceae has been included within Theaceae; however, the APG III system of 2009 places it instead in Pentaphylacaceae.Zygophyllales
The Zygophyllales are an order of dicotyledonous plants, comprising the following two families:
Family KrameriaceaeAccording to the Angiosperm Phylogeny Group (APG II) both families are unplaced to order, but nevertheless included in the Eurosids I. The APG III system of 2009, however, recognized this order. Even if the monogeneric family Krameriaceae shares little common traits with the family Zygophyllaceae, researchers see little advantage in keeping it as a separate family (e.g. Sheahan and Chase). The name Zygophyllales can be used if one finds it appropriate to place both families into an order. The order keeps unchanged in the APG IV system.Under the Cronquist system, the Zygophyllaceae were included within the Sapindales, and the Krameriaceae within the Polygalales.