APG IV system

The APG IV system of flowering plant classification is the fourth version of a modern, mostly molecular-based, system of plant taxonomy for flowering plants (angiosperms) being developed by the Angiosperm Phylogeny Group (APG). It was published in 2016, seven years after its predecessor the APG III system was published in 2009, and 18 years after the first APG system was published in 1998.[1] In 2009, a linear arrangement of the system was published separately;[2] the APG IV paper includes such an arrangement, cross-referenced to the 2009 one.[1]

Compared to the APG III system, the APG IV system recognizes five new orders (Boraginales, Dilleniales, Icacinales, Metteniusales and Vahliales), along with some new families, making a total of 64 angiosperm orders and 416 families.[1] In general, the authors describe their philosophy as "conservative", based on making changes from APG III only where "a well-supported need" has been demonstrated. This has sometimes resulted in placements that are not compatible with published studies, but where further research is needed before the classification can be changed.[3]

Detailed version

Key to symbols used:

* = the family has been added or its circumscription changed since the APG III system of 2009
† = the order has been added since the APG III system

Basal angiosperms

Magnoliids

Independent lineage: unplaced to more inclusive clade

Monocots

Probable sister of eudicots

Eudicots

Core eudicots

Superrosids

Rosids

COM clade; placement uncertain

Rosids continued

Superasterids

Asterids

Phylogeny

Like the earlier APG systems, the APG IV revision is based on a phylogenetic tree for the angiosperms, as shown below.[4]

angiosperms

Amborellales

Nymphaeales

Austrobaileyales

Core angiosperms

Chloranthales

magnoliids

Magnoliales

Laurales

Piperales

Canellales

monocots

Acorales

Alismatales

Petrosaviales

Pandanales

Dioscoreales

Liliales

Asparagales

commelinids

Arecales

Poales

Commelinales

Zingiberales

Ceratophyllales

eudicots

Ranunculales

Proteales

Trochodendrales

Buxales

core eudicots

(continued)

core eudicots

Gunnerales

Pentapetalae

Dilleniales

superrosids

Saxifragales

rosids

Vitales

fabids

Zygophyllales

Fabales

Rosales

Fagales

Cucurbitales

Celastrales

Malpighiales

Oxalidales

malvids

Geraniales

Myrtales

Crossosomatales

Picramniales

Sapindales

Huerteales

Brassicales

Malvales

superasterids

Berberidopsidales

Santalales

Caryophyllales

asterids

Cornales

Ericales

campanulids

Aquifoliales

Asterales

Escalloniales

Bruniales

Apiales

Dipsacales

Paracryphiales

lamiids

Icacinales

Metteniusales

Garryales

Boraginales

Gentianales

Vahliales

Lamiales

Solanales

References

  1. ^ a b c APG IV (2016)
  2. ^ Haston et al. (2009)
  3. ^ APG IV (2016), p. 5
  4. ^ Cole, Hilger & Stevens (2017)

Bibliography

  • Angiosperm Phylogeny Group (2009), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III", Botanical Journal of the Linnean Society, 161 (2): 105–121, doi:10.1111/j.1095-8339.2009.00996.x, archived from the original on 2017-05-25, retrieved 2010-12-10
  • Angiosperm Phylogeny Group (2016), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV", Botanical Journal of the Linnean Society, 181 (1): 1–20, doi:10.1111/boj.12385
  • Haston, E.; Richardson, J.E.; Stevens, P.F.; Chase, M.W. & Harris, D.J. (2009), "The Linear Angiosperm Phylogeny Group (LAPG) III: a linear sequence of the families in APG III" (PDF), Botanical Journal of the Linnean Society, 161 (2): 128–131, doi:10.1111/j.1095-8339.2009.01000.x, retrieved 2016-06-13
  • Fay, Michael (9 May 2016), "APG - classification by consensus", Kew Science, RBG Kew, retrieved 2016-06-12
  • Cole, Theodor C.H.; Hilger, Hartmut H. & Stevens, Peter F. (2017), Angiosperm Phylogeny Poster - Flowering Plant Systematics (PDF), retrieved 2017-07-13

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.

APG system

The APG system (Angiosperm Phylogeny Group system) of plant classification is the first version of a modern, mostly molecular-based, system of plant taxonomy. Published in 1998 by the Angiosperm Phylogeny Group, it was replaced by the improved APG II in 2003, APG III system in 2009 and APG IV system in 2016.

Achariaceae

Achariaceae is a family of flowering plants consisting of 32-33 genera with about 155 species of tropical herbs, shrubs, and trees. The APG IV system has greatly expanded the scope of the family by including many genera previously classified in Flacourtiaceae. Molecular data strongly support the inclusion of this family in the order Malpighiales.

The family is almost exclusively tropical and is best known as the source of chaulmoogra oil, formerly used to treat leprosy. Unlike other members of the former Flacourtiaceae now placed in the family Salicaceae, the genera of Achariaceae typically have cyanogenic glycosides.

Asphodelaceae

Asphodelaceae is a family of flowering plants in the order Asparagales. Such a family has been recognized by most taxonomists, but the circumscription has varied widely. In its current circumscription in the APG IV system, it includes about 40 genera and 900 known species.As defined by the Angiosperm Phylogeny Group in 2009 (the APG III system), the family consisted of three subfamilies: Asphodeloideae, Hemerocallidoideae and Xanthorrhoeoideae. Earlier these three had been treated as separate families.The family Asphodelaceae was made a nomen conservandum (conserved name) in 2017. Previously, the name Xanthorrhoeaceae had priority.. This was anticipated in the APG IV family lists.The family has a wide but scattered distribution throughout the tropics and temperate zones. Many of the species are cultivated as ornamentals. A few are grown commercially for cut flowers. Two species of Aloe are grown for their leaf sap, which has medicinal and cosmetic uses. Xanthorrhoea is endemic to Australia.

In some of the older systems of plant taxonomy, such as the Cronquist system, the plants that now form the family Dasypogonaceae were also considered to belong to this family. Molecular phylogenetic studies have shown that Dasypogonaceae belongs to the commelinids and is therefore not even in the same order as Asphodelaceae.

Asterids

In the APG IV system (2016) for the classification of flowering plants, the name asterids denotes a clade (a monophyletic group). Common examples include the forget-me-nots, nightshades (including potatoes, eggplants, tomatoes, peppers and tobacco), the common sunflower, petunias, morning glory and sweet potato, coffee, lavender, lilac, olive, jasmine, honeysuckle, ash tree, teak, snapdragon, sesame, psyllium, garden sage, table herbs such as mint, basil, and rosemary, and rainforest trees such as Brazil nut.

Most of the taxa belonging to this clade had been referred to the Asteridae in the Cronquist system (1981) and to the Sympetalae in earlier systems. The name asterids (not necessarily capitalised) resembles the earlier botanical name but is intended to be the name of a clade rather than a formal ranked name, in the sense of the ICBN.

Boraginaceae

Boraginaceae, the borage- or forget-me-not family, includes a variety of shrubs, trees, and herbs, totaling about 2,000 species in 146 genera found worldwide.

The APG IV system from 2016 classifies the Boraginaceae as single family of the order Boraginales within the asterids. Under the older Cronquist system it was included in Lamiales, but it is now clear that it is no more similar to the other families in this order than they are to families in several other asterid orders. A revision of the Boraginales, also from 2016, split the Boraginaceae in eleven distinct families: Boraginaceae sensu stricto, Codonaceae, Coldeniaceae, Cordiaceae, Ehretiaceae, Heliotropiaceae, Hoplestigmataceae, Hydrophyllaceae, Lennoaceae, Namaceae, and Wellstediaceae.

These plants have alternately arranged leaves, or a combination of alternate and opposite leaves. The leaf blades usually have a narrow shape; many are linear or lance-shaped. They are smooth-edged or toothed, and some have petioles. Most species have bisexual flowers, but some taxa are dioecious. Most pollination is by hymenopterans, such as bees. Most species have inflorescences that have a coiling shape, at least when new. The flower has a usually five-lobed calyx. The corolla varies in shape from rotate to bell-shaped to tubular, but it generally has five lobes. It can be green, white, yellow, orange, pink, purple, or blue. There are five stamens and one style with one or two stigmas. The fruit is a drupe, sometimes fleshy.Most members of this family have hairy leaves. The coarse character of the hairs is due to cystoliths of silicon dioxide and calcium carbonate. These hairs can induce an adverse skin reaction, including itching and rash in some individuals, particularly among people who handle the plants regularly, such as gardeners. In some species, anthocyanins cause the flowers to change color from red to blue with age. This may be a signal to pollinators that a flower is old and depleted of pollen and nectar.Well-known members of the family include:

alkanet (Alkanna tinctoria)

borage (Borago officinalis)

comfrey (Symphytum spp.)

fiddleneck (Amsinckia spp.)

forget-me-not (Myosotis spp.)

geigertree (Cordia sebestena)

green alkanet (Pentaglottis sempervirens)

heliotrope (Heliotropium spp.)

hound's tongue (Cynoglossum spp.)

lungwort (Pulmonaria spp.)

oysterplant (Mertensia maritima)

purple viper's bugloss/Salvation Jane (Echium plantagineum)

Siberian bugloss (Brunnera macrophylla)

viper's bugloss (Echium vulgare)

Canellales

Canellales is the botanical name for an order of flowering plants, one of the four orders of the magnoliids. It is recognized by the most recent classification of flowering plants, the APG IV system. It is defined to contain two families: Canellaceae and Winteraceae, which comprise 136 species of fragrant trees and shrubs. The Canellaceae are found in tropical America and Africa, and the Winteraceae are part of the Antarctic flora (found in diverse parts of the southern hemisphere). Although the order was defined based on phylogenetic studies, a number of possible synapomorphies have been suggested, relating to the pollen tube, the seeds, the thickness of the integument, and other aspects of the morphology.Until 1999, these two families were not considered to be closely related. Instead the Winteraceae were considered to be a primitive family (due to the structure of the xylem and carpel, a structure which now seems to be derived from xylem and carpels more typical of the angiosperms as a whole). The Canellaceae was often considered to be related to the Myristicaceae. However, studies starting in 1999, based on molecular phylogeny or morphology, have supported uniting these two families.

Commelinids

In plant taxonomy, commelinids (originally commelinoids) (plural, not capitalised) is a name used by the APG IV system for a clade within the monocots, which in its turn is a clade within the angiosperms. The commelinids are the only clade that the APG has informally named within the monocots. The remaining monocots are a paraphyletic unit. Also known as the commelinid monocots it forms one of three groupings within the monocots, and the final branch, the other two groups being the alismatid monocots and the lilioid monocots.

Dasypogonaceae

Dasypogonaceae is a family of flowering plants. Such a family has not been commonly recognized by taxonomists: the plants involved were usually included in the family Xanthorrhoeaceae. Dasypogonaceae includes four genera with 16 species.The APG IV system, of 2016 places the family in order Arecales, after some studies revealed the family as sister to Arecaceae.The earlier APG III of 2009, APG II of 2003, and APG system of 1998, accepted the family and assigns the family to the clade commelinids, unplaced as to order. In turn, the commelinids belong to the monocots.

The family is endemic to Australia, and comprises 16 species in four genera. The best known representative is Kingia australis.

Flacourtiaceae

Flacourtiaceae is a defunct family of flowering plants whose former members have been scattered to various families, mostly to Achariaceae and Salicaceae. It was so vaguely defined that hardly anything seemed out of place there and it became a dumping ground for odd and anomalous genera, gradually making the family even more heterogeneous. In 1975, Hermann Sleumer noted that "Flacourtiaceae as a family is a fiction; only the tribes are homogeneous."In Cronquist's classification, Flacourtiaceae included 79-89 genera and 800-1000 species. Of these, many, including the type genus Flacourtia, have now been transferred to the Salicaceae in the molecular phylogeny-based classification, known as the APG IV system, established by the Angiosperm Phylogeny Group. In the list below, Salicaceae are circumscribed broadly. Some taxonomists further divide Salicaceae sensu lato into three families: Salicaceae sensu stricto, Scyphostegiaceae, and Samydaceae, or into three subfamilies.

Genera formerly included in Flacourtiaceae (current family, and subfamily for Salicaceae, in brackets)

Francoaceae

The Francoaceae Adr.Juss. are a small family of plants in the order Geraniales, including the genera Francoa, commonly known as bridal wreaths, and Tetilla. The Francoaceae are recognized as a family under various classification schemes but under the APG III system the Francoaceae are included within the Melianthaceae. In the APG IV system the Francoaceae are again recognized as a family, with Melianthaceae included in the circumscription of Francoaceae.The Francoaceae are perennial herbs characterized by a basal aggregation of alternate petiolated leaves. The leaf blades (lamina) are either dissected, or entire.

The bridal wreaths are native to Chile. Francoa sonchifolia may grow up to one metre high and produces basal clumps of round, deeply lobed, dark green, fuzzy leaves with winged leafstalks. Compact racemes of small, cup-shaped flowers, which are pink with red markings, appear in summer and early autumn.

Hypoxidaceae

Hypoxidaceae is a family of flowering plants, placed in the order Asparagales of the monocots.The APG IV system of 2016 (unchanged from the 1998, 2003, and 2009 versions) recognizes this family. The family consists of four genera totalling some 160 species.The members of the family are small to medium herbs, with grass-like leaves and an invisible stem, modified into a corm or a rhizome. The flowers are born on leafless shoots, also called scapes. The flowers are trimerous, radially symmetric. The ovary is inferior, developing into a capsule or a berry.

Nepenthales

Nepenthales (Nepenthales Bercht. & J.Presl) is an order of carnivorous flowering plants in the Cronquist system of plant classification.

Nyssaceae

Nyssaceae is a family of flowering trees sometimes included in the dogwood family (Cornaceae). Nyssaceae is composed of 37 known species in the following five genera:

Camptotheca, the happy trees: two species in China

Davidia, the dove tree, handkerchief tree, or ghost tree: one species in central China

Diplopanax: two species in southern China and Vietnam

Mastixia: about nineteen species in Southeast Asia

Nyssa, the tupelos: about 7–10 species in eastern North America and East to Southeast AsiaAmong the extinct genera of the family are Mastixicarpum, very similar to Diplopanax, and Tsukada, an extinct relative of Davidia.

In some treatments, Davidia is split off into its own family, the Davidiaceae. Diplopanax and Mastixia are also sometimes separated into the family Mastixiaceae. The Angiosperm Phylogeny Group APG III system included the genera of Nyssaceae within Cornaceae. The APG IV system recognizes Nyssaceae as a distinct family

Saururaceae

Saururaceae is a plant family comprising four genera and seven species of herbaceous flowering plants native to eastern and southern Asia and North America. The family has been recognised by most taxonomists, and is sometimes known as the "lizard's-tail family". The APG IV system (2016; unchanged from the 2009 APG III system, the 2003 APG II system and the 1998 APG system) assigned it to the order Piperales in the clade magnoliids.

Superasterids

The superasterids are members of a large clade (monophyletic group) of flowering plants, containing more than 122,000 species.

The clade is divided into 20 orders as defined in APG IV system. These orders, in turn, together comprise about 146 families.The name is based upon the name "Asteridae", which had usually been understood to be a subclass.

Superrosids

The superrosids are members of a large clade (monophyletic group) of flowering plants, containing more than 88,000 species, more than a quarter of all angiosperms.The clade is divided into 18 orders as defined in APG IV system. These orders, in turn, together comprise about 155 families.The name is based upon the name "Rosidae", which had usually been understood to be a subclass.

Tecophilaeaceae

Tecophilaeaceae is a family of flowering plants, placed in the order Asparagales of the monocots. It consists of nine genera with a total of 27 species.The family has only recently been recognized by taxonomists. The APG IV system of 2016 (unchanged from the 1998, 2003, and 2009 versions) does recognize this family. The family then includes over half a dozen genera, with only a few dozen species, occurring in Africa, in western South America and western North America. This circumscription includes the genus Cyanastrum, which sometimes has been treated as a separate family Cyanastraceae.

Vahlia

The later homonym Vahlia Dahl is now known as Dombeya.Vahlia is a genus of herbs and subshrubs that grow in Africa and the Indian subcontinent. There are at least five species.

The genus is placed alone in family Vahliaceae. This family had previously been placed in the Saxifragales order, and was reassigned to the new order Vahliales in 2016 by the APG IV system.

Zygophyllales

The Zygophyllales are an order of dicotyledonous plants, comprising the following two families:

Family Zygophyllaceae

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.

Families of angiosperms
Basal angiosperms
Mesangiospermae
Pre-Linnaean
Pre-Darwinian
Post-Darwinian (Phyletic)
Angiosperm Phylogeny Group
System (1998–2009)
See also

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