The Pteridophyte Phylogeny Group (PPG) is an informal international group of systematic botanists who collaborate to establish on the

classification Classification is the activity of assigning objects to some pre-existing classes or categories. This is distinct from the task of establishing the classes themselves (for example through cluster analysis). Examples include diagnostic tests, identif ...

pteridophyte A pteridophyte is a vascular plant (with xylem and phloem) that reproduces by means of spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as " cryptogams", meaning that their means of reproduction is ...

s ( lycophytes and

fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...

s) that reflects knowledge about plant relationships discovered through

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

studies. In 2016, the group published a classification for extant pteridophytes, termed "PPG I". The paper had 94 authors (26 principal and 68 additional). The classification was presented as a consensus classification supported by the community of fern taxonomists. Alternative classifications of ferns exist and are preferred by some.

PPG I

A first classification, PPG I, was produced in 2016, covering only extant (living) pteridophytes. The classification was rank-based, using the ranks of class, subclass, order, suborder, family, subfamily and genus.

Phylogeny

The classification was based on a consensus phylogeny, shown below to the level of order. The very large order Polypodiales was divided into two suborders, as well as families not placed in a suborder:

Classification to subfamily level

To the level of subfamily, the PPG I classification is as follows. * Class

Lycopodiopsida Lycopodiopsida is a class of vascular plants also known as lycopsids, lycopods, or lycophytes. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching stems bearing simple leaves ...

Bartl. (3 orders, 3 families, 18 genera) ::*Order

Lycopodiales The Lycopodiaceae (class Lycopodiopsida, order Lycopodiales) are an old family of vascular plants, including all of the core clubmosses and firmosses, comprising 17 accepted genera and about 500 known species. This family originated about 380 mi ...

DC. ex Bercht. & J.Presl (1 family, 16 genera) ::::*Family

Lycopodiaceae The Lycopodiaceae (class Lycopodiopsida, order Lycopodiales) are an old family of vascular plants, including all of the core clubmosses and firmosses, comprising 17 accepted genera and about 500 known species. This family originated about 380 mi ...

P.Beauv. (16 genera) :::::*Subfamily Lycopodielloideae W.H.Wagner & Beitel ex B.Øllg. (4 genera) :::::*Subfamily

Lycopodioideae ''Lycopodioideae'' is a subfamily in the family Lycopodiaceae in the Pteridophyte Phylogeny Group classification of 2016 (PPG I). It is equivalent to a broad circumscription of the genus '' Lycopodium'' in other classifications. Like all lyco ...

W.H.Wagner & Beitel ex B. Øllg. (9 genera) :::::*Subfamily Huperzioideae W.H.Wagner & Beitel ex B. Øllg. (3 genera) ::*Order Isoëtales Prantl (1 family, 1 genus) ::::*Family Isoëtaceae Dumort. (1 genus) ::*Order Selaginellales Prantl (1 family, 1 genus) ::::*Family

Selaginellaceae ''Selaginella'', also known as spikemosses or lesser clubmosses, is a genus of lycophyte. It is usually treated as the only genus in the family Selaginellaceae, with over 750 known species. This family is distinguished from Lycopodiaceae (the ...

Willk (1 genus) * Class

Polypodiopsida The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...

Cronquist, Takht. & W.Zimm. (11 orders, 48 families, 319 genera) :*Subclass Equisetidae Warm. (1 order, 1 family, 1 genus) ::*Order Equisetales DC. ex Bercht. & J.Presl (1 family, 1 genus) ::::*Family

Equisetaceae Equisetaceae, also known as the horsetail family, is a family of ferns and the only surviving family of the order Equisetales, with one surviving genus, ''Equisetum'', comprising about twenty species. Evolution and systematics Equisetaceae is ...

Michx. ex DC (1 genus) :*Subclass

Ophioglossidae Ophioglossidae is one of the four subclasses of Polypodiopsida (ferns). This subclass consists of the ferns commonly known as whisk ferns, grape ferns, adder's-tongues and moonworts. It is equivalent to the class Psilotopsida in previous treat ...

Klinge (2 orders, 2 families, 12 genera) ::*Order Psilotales Prant (1 family, 2 genera) ::::*Family

Psilotaceae Psilotaceae is a family of ferns (class Polypodiopsida) consisting of two genera, ''Psilotum'' and ''Tmesipteris'' with about a dozen species. It is the only family in the order (biology), order Psilotales. Description Once thought to be descend ...

J.W.Griff. & Henfr. (2 genera) ::*Order Ophioglossales Link (1 family, 10 genera) ::::*Family Ophioglossaceae Martinov (10 genera) :::::*Subfamily Helminthostachyoideae C.Presl (1 genus) :::::*Subfamily Mankyuoideae J.R.Grant & B.Dauphin (1 genus) :::::*Subfamily Ophioglossoideae C.Presl (4 genera) :::::*Subfamily Botrychioideae C.Presl (4 genera) :*Subclass

Marattiidae Marattiaceae is the only family of extant (living) ferns in the order Marattiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), Marattiales is the only order in the subclass Marattiidae. The family has six genera and about ...

Klinge (1 order, 1 family, 6 genera) ::*Order

Marattiales Marattiaceae is the only family of extant (living) ferns in the order Marattiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), Marattiales is the only order in the subclass Marattiidae. The family has six genera and about ...

Link (1 family, 6 genera) ::::*Family Marattiaceae Kaulf (6 genera) :*Subclass Polypodiidae Cronquist, Takht. & W.Zimm. (7 orders, 44 families, 300 genera) ::*Order

Osmundales Osmundaceae (royal fern family) is a family of ferns containing four to six extant genera and 18–25 known species. It is the only living family of the order Osmundales in the class Polypodiopsida (ferns) or in some classifications the only or ...

Link (1 family, 6 genera) ::::*Family Osmundaceae Martinov (6 genera) ::*Order

Hymenophyllales The Hymenophyllaceae, the filmy ferns and bristle ferns, are a family of two to nine genera (depending on classification system) and about 650 known species of ferns, with a subcosmopolitan distribution, but generally restricted to very damp pla ...

A.B.Frank (1 family, 9 genera) ::::*Family Hymenophyllaceae Mart (9 genera) :::::*Subfamily Trichomanoideae C.Presl (8 genera) :::::*Subfamily Hymenophylloideae Burnett (1 genus) ::*Order

Gleicheniales Gleicheniales is an order of ferns in the subclass Polypodiidae (the leptosporangiate ferns). The Gleicheniales has spore records potentially as early as the Early Carboniferous, but the oldest unambiguous macrofossil records date to the Early ...

Schimp (3 families, 10 genera) ::::*Family Matoniaceae C.Pres (2 genera) ::::*Family Dipteridaceae Seward & E.Dale (2 genera) ::::*Family Gleicheniaceae C.Presl (6 genera) ::*Order Schizaeales Schimp. (3 families, 4 genera) ::::*Family Lygodiaceae M.Roem (1 genus) ::::*Family Schizaeaceae Kaulf (2 genera) ::::*Family Anemiaceae Link (1 genus) ::*Order

Salviniales The order Salviniales (formerly known as the Hydropteridales and including the former Marsileales) is an order of ferns in the class Polypodiopsida. Description Salviniales are all aquatic and differ from all other ferns in being heterosporous, ...

Link (2 families, 5 genera) ::::*Family Salviniaceae Martinov (2 genera) ::::*Family

Marsileaceae Marsileaceae () is a small family of heterosporous aquatic and semi-aquatic ferns, though at first sight they do not physically resemble other ferns. The group is commonly known as the "pepperwort family" or as the "water-clover family" becau ...

Mirb. (3 genera) ::*Order

Cyatheales The order Cyatheales, which includes most tree ferns, is a Taxonomy (biology), taxonomic order of the fern class, Polypodiopsida. No clear morphology (biology), morphological features characterize all of the Cyatheales, but DNA sequence data indi ...

A.B.Frank (8 families, 13 genera) ::::*Family Thyrsopteridaceae C.Presl (1 genus) ::::*Family Loxsomataceae C.Presl (2 genera) ::::*Family Culcitaceae Pic.Serm (1 genus) ::::*Family Plagiogyriaceae Bowe (1 genus) ::::*Family Cibotiaceae Koral (1 genus) ::::*Family Metaxyaceae Pic.Serm. (1 genus) ::::*Family Dicksoniaceae M.R.Schomb. (3 genera) ::::*Family

Cyatheaceae The Cyatheaceae are a family of ferns, the scaly tree ferns, one of eight families in the order Cyatheales in the Pteridophyte Phylogeny Group classification of 2016 (PPG I). Alternatively, the family may defined much more broadly (Cyatheaceae ...

Kaulf. (3 genera) ::*Order

Polypodiales The Order (biology), order Polypodiales encompasses the major lineages of polypod ferns, which comprise more than 80% of today's fern species. They are found in many parts of the world including Tropics, tropical, semitropical and Temperate clima ...

Link (26 families, 253 genera) :::*Suborder Saccolomatineae Hovenkamp (1 family, 1 genus) ::::*Family Saccolomataceae Doweld (1 genus) :::*Suborder Lindsaeineae Lehtonen & Tuomist (3 families, 9 genera) ::::*Family Cystodiaceae J.R.Croft (1 genus) ::::*Family Lonchitidaceae Doweld (1 genus) ::::*Family Lindsaeaceae C.Presl ex M.R.Schomb. (7 genera) :::*Suborder Pteridineae J.Prado & Schuettp (1 family, 53 genera) ::::*Family

Pteridaceae Pteridaceae is a family of ferns in the order Polypodiales, including some 1150 known species in ca 45 genera (depending on taxonomic opinions), divided over five subfamilies. The family includes four groups of genera that are sometimes recogni ...

E.D.M.Kirchn. (53 genera) :::::*Subfamily Parkerioideae Burnett (2 genera) :::::*Subfamily Cryptogrammoideae S.Lindsay (3 genera) :::::*Subfamily Pteridoideae Link (13 genera) :::::*Subfamily Vittarioideae Link (12 genera) :::::*Subfamily

Cheilanthoideae Cheilanthoideae is one of the five subfamilies of the fern family Pteridaceae. The subfamily is understood to be monophyletic, but some of the genera as currently defined are not. Most species are xeric-adapted, and the subfamily is most diverse ...

Horvat (23 genera) :::*Suborder Dennstaedtiineae Schwartsb. & Hovenkamp (1 family, 10 genera) ::::*Family Dennstaedtiaceae Lotsy (10 genera) :::*Suborder

Aspleniineae Aspleniineae is a suborder of ferns in the order Polypodiales. It is equivalent to the clade eupolypods II in earlier systems; it is also treated as a single very broadly defined family Aspleniaceae. The suborder generally corresponds with the o ...

H.Schneid. & C.J.Rothf (11 families, 72 genera) ::::*Family Cystopteridaceae Shmakov (3 genera) ::::*Family Rhachidosoraceae X.C.Zhang (1 genus) ::::*Family Diplaziopsidaceae X.C.Zhang & Christenh. (2 genera) ::::*Family Desmophlebiaceae Mynssen (1 genus) ::::*Family Hemidictyaceae Christenh. & H.Schneid. (1 genus) ::::*Family

Aspleniaceae The Aspleniaceae (spleenworts) are a family of ferns, included in the order Polypodiales. The composition and classification of the family have been subject to considerable changes. In particular, there is a narrow circumscription, Aspleniaceae ...

Newman (2 genera) ::::*Family Woodsiaceae Herter (1 genus) ::::*Family Onocleaceae Pic.Serm. (4 genera) ::::*Family Blechnaceae Newman (24 genera) :::::*Subfamily Stenochlaenoideae (Ching) J.P.Roux (3 genera) :::::*Subfamily Woodwardioideae Gasper (3 genera) :::::*Subfamily Blechnoideae Gasper, V.A.O.Dittrich & Salino (18 genera) ::::*Family

Athyriaceae The Athyriaceae (ladyferns and allies) are a family of terrestrial ferns in the order Polypodiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family is placed in the suborder Aspleniineae, and includes two gene ...

Alston (3 genera) ::::*Family

Thelypteridaceae Thelypteridaceae is a family of about 900 species of ferns in the order Polypodiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), it is placed in the suborder Aspleniineae. Alternatively, the family may be submerged in a ...

Ching ex Pic.Serm. (30 genera) :::::*Subfamily Phegopteridoideae Salino, A.R.Sm. & T.E.Almeid (3 genera) :::::*Subfamily Thelypteridoideae C.F.Reed (27 genera) :::*Suborder

Polypodiineae Polypodiineae is a suborder of ferns in the order Polypodiales. It is equivalent to the clade eupolypods I in earlier systems, and to the very broadly defined family Polypodiaceae in the classification of Christenhusz & Chase (2014). It probably ...

Dumort. (9 families, 108 genera) ::::*Family Didymochlaenaceae Ching ex Li Bing Zhang & Liang Zhang (1 genus) ::::*Family Hypodematiaceae Ching (2 genera) ::::*Family

Dryopteridaceae The Dryopteridaceae are a Family (biology), family of leptosporangiate ferns in the Order (biology), order Polypodiales. They are known Common name, colloquially as the wood ferns. In the Pteridophyte Phylogeny Group classification of 2016 (PPG&n ...

Herter (26 genera) :::::*Subfamily

Polybotryoideae Polybotryoideae is a subfamily of the fern family Dryopteridaceae The Dryopteridaceae are a Family (biology), family of leptosporangiate ferns in the Order (biology), order Polypodiales. They are known Common name, colloquially as the wood fe ...

H.M.Liu & X.C.Zhang (7 genera) :::::*Subfamily

Elaphoglossoideae Elaphoglossoideae is a subfamily of the fern family Dryopteridaceae The Dryopteridaceae are a Family (biology), family of leptosporangiate ferns in the Order (biology), order Polypodiales. They are known Common name, colloquially as the wood ...

(Pic.Serm.) Crabbe, Jermy & Mickel (11 genera) :::::*Subfamily Dryopteridoideae Link (6 genera) :::::*2 genera not assigned to a subfamily ::::*Family Nephrolepidaceae Pic.Serm. (1 genus) ::::*Family

Lomariopsidaceae The Lomariopsidaceae is a family of ferns with a largely tropical distribution. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family is placed in the suborder Polypodiineae (eupolypods I) of the order Polypodiales. ...

Alston (4 genera) ::::*Family

Tectariaceae Tectariaceae is a family of leptosporangiate ferns in the order Polypodiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family is placed in the suborder Polypodiineae. Alternatively, it may be treated as the ...

Panigrahi (7 genera) ::::*Family Oleandraceae Ching ex Pic.Serm. (1 genus) ::::*Family Davalliaceae M.R.Schomb. (1 genus) ::::*Family

Polypodiaceae Polypodiaceae is a Family (biology), family of ferns. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family includes around 65 genus, genera and an estimated 1,650 species and is placed in the order Polypodiales, suborder ...

J.Presl & C.Presl (65 genera) :::::*Subfamily Loxogrammoideae H.Schneid. (2 genera) :::::*Subfamily Platycerioideae B.K.Nayar (2 genera) :::::*Subfamily Drynarioideae Crabbe, Jermy & Mickel (6 genera) :::::*Subfamily Microsoroideae B.K.Nayar (12 genera) :::::*Subfamily Polypodioideae Sweet (9 genera) :::::*Subfamily

Grammitidoideae Grammitidoideae is a subfamily of the fern family Polypodiaceae, whose members are informally known as grammitids. It comprises a clade of about 750 species. They are distributed over higher elevations in both the Old World, Old and New World. T ...

Parris & Sundue (33 genera) :::::*1 genus not assigned to a subfamily

Number of genera

The number of genera used in PPG I has proved controversial. PPG I uses 18 lycopod and 319 fern genera. The earlier system put forward by Smith et al. (2006) had suggested a range of 274 to 312 genera for ferns alone. By contrast, the system of Christenhusz and Chase (2014) used 5 lycopod and about 212 fern genera. The number of fern genera was further reduced to 207 in a subsequent publication. The number of genera used in each of these two approaches has been defended by their proponents. Defending PPG I, Schuettpelz et al. (2018) argue that the larger number of genera is a result of "the gradual accumulation of new collections and new data" and hence "a greater appreciation of fern diversity and .an improved ability to distinguish taxa". They also argue that the number of species per genus in the PPG I system is already higher than in other groups of organisms (about 33 species per genus for ferns as opposed to about 22 species per genus for

angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit. T ...

) and that reducing the number of genera as Christenhusz and Chase propose yields the 'excessive' number of about 50 species per genus for ferns. In response, Christenhusz and Chase (2018) argue that the excessive splitting of genera destabilises the usage of names and will lead to greater instability in future, especially when nuclear DNA is employed, and that the highly split genera have few if any characters that can be used to recognize them, making identification difficult, even to generic level. They further argue that comparing numbers of species per genus in different groups is "fundamentally meaningless", because there is no limit to numbers of species per genus. They also argue that the new findings in phylogeny can easily be treated at subgeneric and subfamilial levels, so that the names used by non-specialists will remain unaltered.

References

{{Fern classification Botany organizations Plant taxonomy Taxonomy (biology) organizations Systems of plant taxonomy

PPG I

Phylogeny

Classification to subfamily level

Number of genera

See also

References